ORCID Profile
0000-0002-4619-8361
Current Organisation
University of Western Australia
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Other Biological Sciences | Global Change Biology | Environmental Science and Management | Climatology (Incl. Palaeoclimatology) | Atmospheric Sciences | Terrestrial Ecology | Global Change Biology | Atmospheric Sciences Not Elsewhere Classified | Physical Geography and Environmental Geoscience | Climatology (excl. Climate Change Processes) | Information Systems Management | Natural Resource Management | Environmental Monitoring | Water Resources Engineering | Ecosystem Function | Physical Geography | Oceanography Not Elsewhere Classified | Natural Resource Management | Fire Management | Atmospheric Dynamics | Environmental Management And Rehabilitation | Surfacewater Hydrology | Environmental Engineering not elsewhere classified | Conservation and Biodiversity | Soil And Water Sciences Not Elsewhere Classified | Landscape Ecology | Surface Processes | Photogrammetry and Remote Sensing | Ecological Applications | Environmental Engineering | Soil Biology | Land Capability And Soil Degradation | Meteorology | Agricultural Hydrology (Drainage, Flooding, Irrigation, Quality, etc.) | Forestry Management and Environment | Agricultural Spatial Analysis and Modelling |
ANZSRC Socio-Economic Objective (SEO)
Climate change | Land and water management | Sparseland, Permanent Grassland and Arid Zone Land and Water Management | Land and water management | Land and water management | Global climate change adaptation measures | Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Living resources (flora and fauna) | Atmospheric composition | Forest and Woodlands Water Management | Weather | Hardwood plantations | Native forests | Management of Greenhouse Gas Emissions from Animal Production | Biological sciences | Integration of Farm and Forestry | Climate variability | Weather | Air quality | Beef cattle | Climate Change Mitigation Strategies | Land and water management | Integrated (ecosystem) assessment and management | Environmental policy, legislation and standards not elsewhere classified | Scientific instrumentation | Natural Hazards in Fresh, Ground and Surface Water Environments | Management of Greenhouse Gas Emissions from Plant Production | Farmland, Arable Cropland and Permanent Cropland Water Management
Related Links
Publications
Gross primary productivity and water use efficiency are increasing in a high rainfall tropical savanna
Publisher: Wiley
Date: 23-12-2022
DOI: 10.1111/GCB.16012
Abstract: Despite their size and contribution to the global carbon cycle, we have limited understanding of tropical savannas and their current trajectory with climate change and anthropogenic pressures. Here we examined interannual variability and externally forced long‐term changes in carbon and water exchange from a high rainfall savanna site in the seasonal tropics of north Australia. We used an 18‐year flux data time series (2001–2019) to detect trends and drivers of fluxes of carbon and water. Significant positive trends in gross primary productivity (GPP, 15.4 g C m 2 year −2 ), ecosystem respiration ( R eco , 8.0 g C m 2 year −2 ), net ecosystem productivity (NEE, 7.4 g C m 2 year −2 ) and ecosystem water use efficiency (WUE, 0.0077 g C kg H 2 O −1 year −1 ) were computed. There was a weaker, non‐significant trend in latent energy exchange (LE, 0.34 W m −2 year −1 ). Rainfall from a nearby site increased statistically over a 45‐year period during the observation period. To examine the dominant drivers of changes in GPP and WUE, we used a random forest approach and a terrestrial biosphere model to conduct an attribution experiment. Radiant energy was the dominant driver of wet season fluxes, whereas soil water content dominated dry season fluxes. The model attribution suggested that [CO 2 ], precipitation and T air accounting for 90% of the modelled trend in GPP and WUE. Positive trends in fluxes were largest in the dry season implying tree components were a larger contributor than the grassy understorey. Fluxes and environmental drivers were not significant during the wet season, the period when grasses are active. The site is potentially still recovering from a cyclone 45 years ago and regrowth from this event may also be contributing to the observed trends in sequestration, highlighting the need to understand fluxes and their drivers from sub‐diurnal to decadal scales.
Seasonal, interannual and decadal drivers of tree and grass productivity in an Australian tropical savanna
Publisher: Wiley
Date: 28-02-2018
DOI: 10.1111/GCB.14072
Abstract: Tree-grass savannas are a widespread biome and are highly valued for their ecosystem services. There is a need to understand the long-term dynamics and meteorological drivers of both tree and grass productivity separately in order to successfully manage savannas in the future. This study investigated the interannual variability (IAV) of tree and grass gross primary productivity (GPP) by combining a long-term (15 year) eddy covariance flux record and model estimates of tree and grass GPP inferred from satellite remote sensing. On a seasonal basis, the primary drivers of tree and grass GPP were solar radiation in the wet season and soil moisture in the dry season. On an interannual basis, soil water availability had a positive effect on tree GPP and a negative effect on grass GPP. No linear trend in the tree-grass GPP ratio was observed over the 15-year study period. However, the tree-grass GPP ratio was correlated with the modes of climate variability, namely the Southern Oscillation Index. This study has provided insight into the long-term contributions of trees and grasses to savanna productivity, along with their respective meteorological determinants of IAV.
Estimation of high-resolution terrestrial evapotranspiration from Landsat data using a simple Taylor skill fusion method
Publisher: Elsevier BV
Date: 10-2017
Urban water storage capacity inferred from observed evapotranspiration recession
Publisher: Wiley
Date: 23-06-2021
Net landscape carbon balance of a tropical savanna: Relative importance of fire and aquatic export in offsetting terrestrial production
Publisher: Wiley
Date: 13-08-2020
DOI: 10.1111/GCB.15287
Urban water storage capacity inferred from observed evapotranspiration recession
Publisher: Wiley
Date: 22-09-2021
A comparison of gap-filling algorithms for eddy covariance fluxes and their drivers
Publisher: Copernicus GmbH
Date: 07-09-2020
DOI: 10.5194/GI-2020-21
Abstract: Abstract. The errors and uncertainties associated with gap-filling algorithms of water, carbon and energy fluxes data, have always been one of the prominent challenges of the global network of microclimatological tower sites that use eddy covariance (EC) technique. To address this concern, and find more efficient gap-filling algorithms, we reviewed eight algorithms to estimate missing values of environmental drivers, and separately three major fluxes in EC time series. We then examined the performance of mentioned algorithms for different gap-filling scenarios utilising data from five OzFlux Network towers during 2013. The objectives of this research were (a) to evaluate the impact of training and testing window lengths on the performance of each algorithm (b) to compare the performance of traditional and new gap-filling techniques for the EC data, for fluxes and their corresponding meteorological drivers. The performance of algorithms was evaluated by generating nine different training-testing window lengths, ranging from a day to 365 days. In each scenario, the gaps covered the data for the entirety of 2013 by consecutively repeating them, where, in each step, values were modelled by using earlier window data. After running each scenario, a variety of statistical metrics was used to evaluate the performance of the algorithms. The algorithms showed different levels of sensitivity to training-testing windows The Prophet Forecast Model (FBP) revealed the most sensitivity, whilst the performance of artificial neural networks (ANNs), for instance, did not vary considerably by changing the window length. The performance of the algorithms generally decreased with increasing training-testing window length, yet the differences were not considerable for the windows smaller than 60 days. Gap-filling of the environmental drivers showed there was not a significant difference amongst the algorithms, the linear algorithms showed slight superiority over those of machine learning (ML), except the random forest algorithm estimating the ground heat flux (RMSEs of 30.17 and 34.93 for RF and CLR respectively). For the major fluxes, though, ML algorithms showed superiority (9 % less RMSE on average), except the Support Vector Regression (SVR), which provided significant bias in its estimations. Even though ANNs, random forest (RF) and extreme gradient boost (XGB) showed close performance in gap-filling of the major fluxes, RF provided more consistent results with less bias, relatively. The results indicated that there is no single algorithm which outperforms in all situations and therefore, but RF is a potential alternative for the ANNs as regards flux gap-filling.
Watering our cities: The capacity for Water Sensitive Urban Design to support urban cooling and improve human thermal comfort in the Australian context
Publisher: SAGE Publications
Date: 06-11-2013
Abstract: Urban drainage infrastructure is generally designed to rapidly export stormwater away from the urban environment to minimize flood risk created by extensive impervious surface cover. This deficit is resolved by importing high-quality potable water for irrigation. However, cities and towns at times face water restrictions in response to drought and water scarcity. This can exacerbate heating and drying, and promote the development of unfavourable urban climates. The combination of excessive heating driven by urban development, low water availability and future climate change impacts could compromise human health and amenity for urban dwellers. This paper draws on existing literature to demonstrate the potential of Water Sensitive Urban Design (WSUD) to help improve outdoor human thermal comfort in urban areas and support Climate Sensitive Urban Design (CSUD) objectives within the Australian context. WSUD provides a mechanism for retaining water in the urban landscape through stormwater harvesting and reuse while also reducing urban temperatures through enhanced evapotranspiration and surface cooling. Research suggests that WSUD features are broadly capable of lowering temperatures and improving human thermal comfort, and when integrated with vegetation (especially trees) have potential to meet CSUD objectives. However, the degree of benefit (the intensity of cooling and improvements to human thermal comfort) depends on a multitude of factors including local environmental conditions, the design and placement of the systems, and the nature of the surrounding urban landscape. We suggest that WSUD can provide a source of water across Australian urban environments for landscape irrigation and soil moisture replenishment to maximize the urban climatic benefits of existing vegetation and green spaces. WSUD should be implemented strategically into the urban landscape, targeting areas of high heat exposure, with many distributed WSUD features at regular intervals to promote infiltration and evapotranspiration, and maintain tree health.
Response of savanna gross primary productivity to interannual variability in rainfall
Publisher: SAGE Publications
Date: 13-06-2013
Abstract: Studying the temporal pattern of savanna gross primary productivity (GPP) is essential for predicting the response of the biome to global environmental changes. In this study, MODIS satellite data coupled with eddy covariance based flux measurements were used to estimate GPP using a remote sensing based light use efficiency model across a significant rainfall gradient in the Northern Territory (NT) region of Australia. Closed forest that occurred in wet and often fireproof environments assimilated (GPP) 4–6 times more carbon than grasslands and Acacia woodlands that grow in arid environments ( mm annual rainfall). However, due to their small spatial extent, closed forests contributed .5% of the regional budget compared to savanna woodlands (86%) and grasslands (32%). Annual rainfall was found to exert a significant influence on GPP for different vegetation types except for closed forest which was less sensitive to above-average rainfall. Interannual variability in GPP showed that arid ecosystems had a higher variation ( %) compared to woodlands and forest (∼5%). This variation in GPP was correlated with that of rainfall (R 2 = 0.88, p .05). Analysis of the impact of wettest and driest years on GPP showed a strong positive correlation between the magnitude of the relative maxima in rainfall and maxima in GPP (R 2 = 0.89, p .05). In contrast, the relative rainfall minima exhibited an insignificant relationship with relative GPP minima (R 2 = 0.45, p = 0.07). These findings provide valuable information on the carbon uptake across the savanna biome and show the sensitivity of different vegetation systems to rainfall, a variable that may change in quantity and variability with projected climate change. Such data also show regions of high levels of carbon that could be linked with savanna management to protect the resources in the Australian savannas.
Means and extremes: building variability into community-level climate change experiments
Publisher: Wiley
Date: 26-02-2013
DOI: 10.1111/ELE.12095
Abstract: Experimental studies assessing climatic effects on ecological communities have typically applied static warming treatments. Although these studies have been informative, they have usually failed to incorporate either current or predicted future, patterns of variability. Future climates are likely to include extreme events which have greater impacts on ecological systems than changes in means alone. Here, we review the studies which have used experiments to assess impacts of temperature on marine, freshwater and terrestrial communities, and classify them into a set of 'generations' based on how they incorporate variability. The majority of studies have failed to incorporate extreme events. In terrestrial ecosystems in particular, experimental treatments have reduced temperature variability, when most climate models predict increased variability. Marine studies have tended to not concentrate on changes in variability, likely in part because the thermal mass of oceans will moderate variation. In freshwaters, climate change experiments have a much shorter history than in the other ecosystems, and have tended to take a relatively simple approach. We propose a new 'generation' of climate change experiments using down-scaled climate models which incorporate predicted changes in climatic variability, and describe a process for generating data which can be applied as experimental climate change treatments.
Author Correction: The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data
Publisher: Springer Science and Business Media LLC
Date: 25-02-2021
DOI: 10.1038/S41597-021-00851-9
Abstract: A Correction to this paper has been published: 0.1038/s41597-021-00851-9.
Supplementary material to "Does maximization of net carbon profit enable the prediction of vegetation behaviour in savanna sites along a precipitation gradient?"
Publisher: Copernicus GmbH
Date: 11-06-2021
OzFlux data: network integration from collection to curation
Publisher: Copernicus GmbH
Date: 19-06-2017
Abstract: Abstract. Measurement of the exchange of energy and mass between the surface and the atmospheric boundary-layer by the eddy covariance technique has undergone great change in the last 2 decades. Early studies of these exchanges were confined to brief field c aigns in carefully controlled conditions followed by months of data analysis. Current practice is to run tower-based eddy covariance systems continuously over several years due to the need for continuous monitoring as part of a global effort to develop local-, regional-, continental- and global-scale budgets of carbon, water and energy. Efficient methods of processing the increased quantities of data are needed to maximise the time available for analysis and interpretation. Standardised methods are needed to remove differences in data processing as possible contributors to observed spatial variability. Furthermore, public availability of these data sets assists with undertaking global research efforts. The OzFlux data path has been developed (i) to provide a standard set of quality control and post-processing tools across the network, thereby facilitating inter-site integration and spatial comparisons (ii) to increase the time available to researchers for analysis and interpretation by reducing the time spent collecting and processing data (iii) to propagate both data and metadata to the final product and (iv) to facilitate the use of the OzFlux data by adopting a standard file format and making the data available from web-based portals. Discovery of the OzFlux data set is facilitated through incorporation in FLUXNET data syntheses and the publication of collection metadata via the RIF-CS format. This paper serves two purposes. The first is to describe the data sets, along with their quality control and post-processing, for the other papers of this Special Issue. The second is to provide an ex le of one solution to the data collection and curation challenges that are encountered by similar flux tower networks worldwide.
An investigation of the sensitivity of a land surface model to climate change using a reduced form model
Publisher: Springer Science and Business Media LLC
Date: 07-05-2001
Urban water storage capacity inferred from observed evapotranspiration recession
Publisher: Wiley
Date: 26-03-2021
Initial results from Phase 2 of the international urban energy balance model comparison
Publisher: Wiley
Date: 07-10-2010
DOI: 10.1002/JOC.2227
Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes
Publisher: Wiley
Date: 24-02-2002
A Surface Temperature Initiated Closure (STIC) for surface energy balance fluxes
Publisher: Elsevier BV
Date: 02-2014
A remote sensing‐based three‐source energy balance model to improve global estimations of evapotranspiration in semi‐arid tree‐grass ecosystems
Publisher: Wiley
Date: 02-12-2021
DOI: 10.1111/GCB.16002
Abstract: It is well documented that energy balance and other remote sensing‐based evapotranspiration (ET) models face greater uncertainty over water‐limited tree‐grass ecosystems (TGEs), representing nearly 1/6th of the global land surface. Their dual vegetation strata, the grass‐dominated understory and tree‐dominated overstory, make for distinct structural, physiological and phenological characteristics, which challenge models compared to more homogeneous and energy‐limited ecosystems. Along with this, the contribution of grasses and trees to total transpiration ( T ), along with their different climatic drivers, is still largely unknown nor quantified in TGEs. This study proposes a thermal‐based three‐source energy balance (3SEB) model, accommodating an additional vegetation source within the well‐known two‐source energy balance (TSEB) model. The model was implemented at both tower and continental scales using eddy‐covariance (EC) TGE sites, with variable tree canopy cover and rainfall ( P ) regimes and Meteosat Second Generation (MSG) images. 3SEB robustly simulated latent heat (LE) and related energy fluxes in all sites (Tower: LE RMSD ~60 W/m 2 MSG: LE RMSD ~90 W/m 2 ), improving over both TSEB and seasonally changing TSEB (TSEB‐2S) models. In addition, 3SEB inherently partitions water fluxes between the tree, grass and soil sources. The modelled T correlated well with EC T estimates ( r .76), derived from a machine learning ET partitioning method. The T /ET was found positively related to both P and leaf area index, especially compared to the decomposed grass understory T /ET. However, trees and grasses had contrasting relations with respect to monthly P . These results demonstrate the importance in decomposing total ET into the different vegetation sources, as they have distinct climatic drivers, and hence, different relations to seasonal water availability. These promising results improved ET and energy flux estimations over complex TGEs, which may contribute to enhance global drought monitoring and understanding, and their responses to climate change feedbacks.
Reviews and syntheses: Australian vegetation phenology: New insights from satellite remote sensing and digital repeat photography
Publisher: Copernicus GmbH
Date: 13-09-2016
Abstract: Abstract. Phenology is the study of periodic biological occurrences and can provide important insights into the influence of climatic variability and change on ecosystems. Understanding Australia's vegetation phenology is a challenge due to its erse range of ecosystems, from savannas and tropical rainforests to temperate eucalypt woodlands, semi-arid scrublands, and alpine grasslands. These ecosystems exhibit marked differences in seasonal patterns of canopy development and plant life-cycle events, much of which deviates from the predictable seasonal phenological pulse of temperate deciduous and boreal biomes. Many Australian ecosystems are subject to irregular events (i.e. drought, flooding, cyclones, and fire) that can alter ecosystem composition, structure, and functioning just as much as seasonal change. We show how satellite remote sensing and ground-based digital repeat photography (i.e. phenocams) can be used to improve understanding of phenology in Australian ecosystems. First, we examine temporal variation in phenology on the continental scale using the enhanced vegetation index (EVI), calculated from MODerate resolution Imaging Spectroradiometer (MODIS) data. Spatial gradients are revealed, ranging from regions with pronounced seasonality in canopy development (i.e. tropical savannas) to regions where seasonal variation is minimal (i.e. tropical rainforests) or high but irregular (i.e. arid ecosystems). Next, we use time series colour information extracted from phenocam imagery to illustrate a range of phenological signals in four contrasting Australian ecosystems. These include greening and senescing events in tropical savannas and temperate eucalypt understorey, as well as strong seasonal dynamics of in idual trees in a seemingly static evergreen rainforest. We also demonstrate how phenology links with ecosystem gross primary productivity (from eddy covariance) and discuss why these processes are linked in some ecosystems but not others. We conclude that phenocams have the potential to greatly improve the current understanding of Australian ecosystems. To facilitate the sharing of this information, we have formed the Australian Phenocam Network (phenocam.org.au/).
A spatially explicit land surface phenology data product for science, monitoring and natural resources management applications
Publisher: Elsevier BV
Date: 02-2015
Preface: OzFlux: a network for the study of ecosystem carbon and water dynamics across Australia and New Zealand
Publisher: Copernicus GmbH
Date: 16-01-2018
Ecosystem Function in Savannas
Publisher: CRC Press
Date: 17-11-2010
DOI: 10.1201/B10275
Is productivity of mesic savannas light limited or water limited? Results of a simulation study
Publisher: Wiley
Date: 15-04-2011
Fire in Australian savannas: from leaf to landscape
Publisher: Wiley
Date: 09-09-2014
DOI: 10.1111/GCB.12686
Abstract: Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km 2 ) and provide significant ecosystem services through carbon and water cycles and the maintenance of bio ersity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.
Evaluation of Collections 4 and 5 of the MODIS Gross Primary Productivity product and algorithm improvement at a tropical savanna site in northern Australia
Publisher: Elsevier BV
Date: 09-2009
Net ecosystem carbon exchange of a dry temperate eucalypt forest
Publisher: Copernicus GmbH
Date: 23-08-2017
Abstract: Abstract. Forest ecosystems play a crucial role in the global carbon cycle by sequestering a considerable fraction of anthropogenic CO2, thereby contributing to climate change mitigation. However, there is a gap in our understanding about the carbon dynamics of eucalypt (broadleaf evergreen) forests in temperate climates, which might differ from temperate evergreen coniferous or deciduous broadleaved forests given their fundamental differences in physiology, phenology and growth dynamics. To address this gap we undertook a 3-year study (2010–2012) of eddy covariance measurements in a dry temperate eucalypt forest in southeastern Australia. We determined the annual net carbon balance and investigated the temporal (seasonal and inter-annual) variability in and environmental controls of net ecosystem carbon exchange (NEE), gross primary productivity (GPP) and ecosystem respiration (ER). The forest was a large and constant carbon sink throughout the study period, even in winter, with an overall mean NEE of −1234 ± 109 (SE) g C m−2 yr−1. Estimated annual ER was similar for 2010 and 2011 but decreased in 2012 ranging from 1603 to 1346 g C m−2 yr−1, whereas GPP showed no significant inter-annual variability, with a mean annual estimate of 2728 ± 39 g C m−2 yr−1. All ecosystem carbon fluxes had a pronounced seasonality, with GPP being greatest during spring and summer and ER being highest during summer, whereas peaks in NEE occurred in early spring and again in summer. High NEE in spring was likely caused by a delayed increase in ER due to low temperatures. A strong seasonal pattern in environmental controls of daytime and night-time NEE was revealed. Daytime NEE was equally explained by incoming solar radiation and air temperature, whereas air temperature was the main environmental driver of night-time NEE. The forest experienced unusual above-average annual rainfall during the first 2 years of this 3-year period so that soil water content remained relatively high and the forest was not water limited. Our results show the potential of temperate eucalypt forests to sequester large amounts of carbon when not water limited. However, further studies using bottom-up approaches are needed to validate measurements from the eddy covariance flux tower and to account for a possible underestimation in ER due to advection fluxes.
Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia
Publisher: Elsevier BV
Date: 11-2011
The role of aerodynamic resistance in thermal remote sensing-based evapotranspiration models
Publisher: Elsevier BV
Date: 10-2021
On the temporal upscaling of evapotranspiration from instantaneous remote sensing measurements to 8-day mean daily-sums
Publisher: Elsevier BV
Date: 2012
Global parameterization and validation of a two‐leaf light use efficiency model for predicting gross primary production across FLUXNET sites
Publisher: American Geophysical Union (AGU)
Date: 04-2016
DOI: 10.1002/2014JG002876
Does afforestation of pastures increase sequestration of soil carbon in Mediterranean climates?
Publisher: Elsevier BV
Date: 09-2012
Impacts of fire on forest age and runoff in mountain ash forests — RETRACTED
Publisher: CSIRO Publishing
Date: 2008
DOI: 10.1071/FP08120
Occasional large emissions of nitrous oxide and methane observed in stormwater biofiltration systems
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.SCITOTENV.2013.01.035
Abstract: Designed, green infrastructures are becoming a customary feature of the urban landscape. Sustainable technologies for stormwater management, and biofilters in particular, are increasingly used to reduce stormwater runoff volumes and peaks as well as improve the water quality of runoff discharged into urban water bodies. Although a lot of research has been devoted to these technologies, their effect in terms of greenhouse gas fluxes in urban areas has not been yet investigated. We present the first study aimed at quantifying greenhouse gas fluxes between the soil of stormwater biofilters and the atmosphere. N2O, CH4, and CO2 were measured periodically over a year in two operational vegetated biofiltration cells at Monash University in Melbourne, Australia. One cell had a saturated zone at the bottom, and compost and hardwood mulch added to the sandy loam filter media. The other cell had no saturated zone and was composed of sandy loam. Similar sedges were planted in both cells. The biofilter soil was a small N2O source and a sink for CH4 for most measurement events, with occasional large emissions of both N2O and CH4 under very wet conditions. Average N2O fluxes from the cell with the saturated zone were almost five-fold greater (65.6 μg N2O-N m(-2) h(-1)) than from the other cell (13.7 μg N2O-N m(-2) h(-1)), with peaks up to 1100 μg N2O-N m(-2) h(-1). These N2O fluxes are of similar magnitude to those measured in other urban soils, but with larger peak emissions. The CH4 sink strength of the cell with the saturated zone (-3.8 μg CH4-C m(-2) h(-1)) was lower than the other cell (-18.3 μg CH4-C m(-2) h(-1)). Both cells of the biofilter appeared to take up CH4 at similar rates to other urban lawn systems however, the biofilter cells displayed occasional large CH4 emissions following inflow events, which were not seen in other urban systems. CO2 fluxes increased with soil temperature in both cells, and in the cell without the saturated zone CO2 fluxes decreased as soil moisture increased. Other studies of CO2 fluxes from urban soils have found both similar and larger CO2 emissions than those measured in the biofilter. The results of this study suggest that the greenhouse gas footprint of stormwater treatment warrant consideration in the planning and implementation of engineered green infrastructures.
Interactions between nocturnal turbulent flux, storage and advection at an ideal eucalypt woodland site
Publisher: Copernicus GmbH
Date: 22-06-2017
Abstract: Abstract. While the eddy covariance technique has become an important technique for estimating long-term ecosystem carbon balance, under certain conditions the measured turbulent flux of CO2 at a given height above an ecosystem does not represent the true surface flux. Profile systems have been deployed to measure periodic storage of CO2 below the measurement height, but have not been widely adopted. This is most likely due to the additional expense and complexity and possibly also the perception, given that net storage over intervals exceeding 24 h is generally negligible, that these measurements are not particularly important. In this study, we used a 3-year record of net ecosystem exchange of CO2 and simultaneous measurements of CO2 storage to ascertain the relative contributions of turbulent CO2 flux, storage, and advection (calculated as a residual quantity) to the nocturnal CO2 balance and to quantify the effect of neglecting storage. The conditions at the site are in relative terms highly favourable for eddy covariance measurements, yet we found a substantial contribution (∼ 40 %) of advection to nocturnal turbulent flux underestimation. The most likely mechanism for advection is cooling-induced drainage flows, the effects of which were observed in the storage measurements. The remaining ∼ 60 % of flux underestimation was due to storage of CO2. We also showed that substantial underestimation of carbon uptake (approximately 80 gC m−2 a−1, or 25 % of annual carbon uptake) arose when standard methods (u∗ filtering) of nocturnal flux correction were implemented in the absence of storage estimates. These biases were reduced to approximately 40–45 gC m−2 a−1 when the filter was applied over the entire diel period, but they were nonetheless large relative to quantifiable uncertainties in the data. Neglect of storage also distorted the relationships between the CO2 exchange processes (respiration and photosynthesis) and their key controls (light and temperature respectively). We conclude that the addition of storage measurements to eddy covariance sites with all but the lowest measurement heights should be a high priority for the flux measurement community.
Coupling carbon allocation with leaf and root phenology predicts tree-grass partitioning along a savanna rainfall gradient
Publisher: Copernicus GmbH
Date: 05-10-2015
DOI: 10.5194/BGD-12-16313-2015
Abstract: Abstract. The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree/grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximise long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for ex le, within the framework of a global biogeochemical model. We demonstrate the approach by encoding it in a new simple carbon/water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely-sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at 5 tower sites along the Northern Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area and foliage projective cover along the NATT. The model behaviour emerges from complex feed-backs between the plant physiology and vegetation dynamics, mediated by shifting above- vs. below-ground resources, and not from imposed hypotheses about the controls on tree/grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.
Author response
Publisher: Copernicus GmbH
Date: 30-08-2016
Ecological Climatology: Concepts and Applications, 2nd edition
Publisher: Wiley
Date: 30-04-2010
Parameterization of an ecosystem light-use-efficiency model for predicting savanna GPP using MODIS EVI
Publisher: Elsevier BV
Date: 11-2014
Balancing the environmental benefits of reforestation in agricultural regions
Publisher: Elsevier BV
Date: 07-2015
The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data
Publisher: Springer Science and Business Media LLC
Date: 09-07-2020
DOI: 10.1038/S41597-020-0534-3
Abstract: The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.
Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO) response to reviewer comments
Publisher: Copernicus GmbH
Date: 24-09-2016
The nature of spatial transitions in the Arctic
Publisher: Wiley
Date: 25-11-2004
Does maximization of net carbon profit enable the prediction of vegetation behaviour in savanna sites along a precipitation gradient?
Publisher: Copernicus GmbH
Date: 02-2022
Abstract: Abstract. Most terrestrial biosphere models (TBMs) rely on more or less detailed information about the properties of the local vegetation. In contrast, optimality-based models require much less information about the local vegetation as they are designed to predict vegetation properties based on general principles related to natural selection and physiological limits. Although such models are not expected to reproduce current vegetation behaviour as closely as models that use local information, they promise to predict the behaviour of natural vegetation under future conditions, including the effects of physiological plasticity and shifts of species composition, which are difficult to capture by extrapolation of past observations. A previous model intercomparison using conventional TBMs revealed a range of deficiencies in reproducing water and carbon fluxes for savanna sites along a precipitation gradient of the North Australian Tropical Transect (Whitley et al., 2016). Here, we examine the ability of an optimality-based model (the Vegetation Optimality Model, VOM) to predict vegetation behaviour for the same savanna sites. The VOM optimizes key vegetation properties such as foliage cover, rooting depth and water use parameters in order to maximize the net carbon profit (NCP), defined as the difference between total carbon taken up by photosynthesis minus the carbon invested in construction and maintenance of plant organs. Despite a reduced need for input data, the VOM performed similarly to or better than the conventional TBMs in terms of reproducing the seasonal litude and mean annual fluxes recorded by flux towers at the different sites. It had a relative error of 0.08 for the seasonal litude in ET and was among the three best models tested with the smallest relative error in the seasonal litude of gross primary productivity (GPP). Nevertheless, the VOM displayed some persistent deviations from observations, especially for GPP, namely an underestimation of dry season evapotranspiration at the wettest site, suggesting that the hydrological assumptions (free drainage) have a strong influence on the results. Furthermore, our study exposes a persistent overprediction of vegetation cover and carbon uptake during the wet seasons by the VOM. Our analysis revealed several areas for improvement in the VOM and the applied optimality theory, including a better representation of the hydrological settings as well as the costs and benefits related to plant water transport and light capture by the canopy. The results of this study imply that vegetation optimality is a promising approach to explain vegetation dynamics and the resulting fluxes. It provides a way to derive vegetation properties independently of observations and allows for a more insightful evaluation of model shortcomings as no calibration or site-specific information is required.
Bridge to the future: Important lessons from 20 years of ecosystem observations made by the OzFlux network
Publisher: Wiley
Date: 22-03-2022
DOI: 10.1111/GCB.16141
Abstract: In 2020, the Australian and New Zealand flux research and monitoring network, OzFlux, celebrated its 20 th anniversary by reflecting on the lessons learned through two decades of ecosystem studies on global change biology. OzFlux is a network not only for ecosystem researchers, but also for those ‘next users’ of the knowledge, information and data that such networks provide. Here, we focus on eight lessons across topics of climate change and variability, disturbance and resilience, drought and heat stress and synergies with remote sensing and modelling. In distilling the key lessons learned, we also identify where further research is needed to fill knowledge gaps and improve the utility and relevance of the outputs from OzFlux. Extreme climate variability across Australia and New Zealand (droughts and flooding rains) provides a natural laboratory for a global understanding of ecosystems in this time of accelerating climate change. As evidence of worsening global fire risk emerges, the natural ability of these ecosystems to recover from disturbances, such as fire and cyclones, provides lessons on adaptation and resilience to disturbance. Drought and heatwaves are common occurrences across large parts of the region and can tip an ecosystem's carbon budget from a net CO 2 sink to a net CO 2 source. Despite such responses to stress, ecosystems at OzFlux sites show their resilience to climate variability by rapidly pivoting back to a strong carbon sink upon the return of favourable conditions. Located in under‐represented areas, OzFlux data have the potential for reducing uncertainties in global remote sensing products, and these data provide several opportunities to develop new theories and improve our ecosystem models. The accumulated impacts of these lessons over the last 20 years highlights the value of long‐term flux observations for natural and managed systems. A future vision for OzFlux includes ongoing and newly developed synergies with ecophysiologists, ecologists, geologists, remote sensors and modellers.
Behavior of multitemporal and multisensor passive microwave indices in Southern Hemisphere ecosystems
Publisher: American Geophysical Union (AGU)
Date: 12-2014
DOI: 10.1002/2014JG002626
Investigating the Short-term Effects of Air Pollution on Daily Mortality Among the Elderly Using Generalized Additive Distributed Lag Modelling
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2011
The influence of subtropical cold fronts on the surface energy balance of a semi-arid site
Publisher: Elsevier BV
Date: 04-2000
Technical note: Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO)
Publisher: Copernicus GmbH
Date: 23-03-2017
Abstract: Abstract. Standardised, quality-controlled and robust data from flux networks underpin the understanding of ecosystem processes and tools necessary to support the management of natural resources, including water, carbon and nutrients for environmental and production benefits. The Australian regional flux network (OzFlux) currently has 23 active sites and aims to provide a continental-scale national research facility to monitor and assess Australia's terrestrial biosphere and climate for improved predictions. Given the need for standardised and effective data processing of flux data, we have developed a software suite, called the Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO), that enables gap-filling and partitioning of the primary fluxes into ecosystem respiration (Fre) and gross primary productivity (GPP) and subsequently provides diagnostics and results. We outline the processing pathways and methodologies that are applied in DINGO (v13) to OzFlux data, including (1) gap-filling of meteorological and other drivers (2) gap-filling of fluxes using artificial neural networks (3) the u* threshold determination (4) partitioning into ecosystem respiration and gross primary productivity (5) random, model and u* uncertainties and (6) diagnostic, footprint calculation, summary and results outputs. DINGO was developed for Australian data, but the framework is applicable to any flux data or regional network. Quality data from robust systems like DINGO ensure the utility and uptake of the flux data and facilitates synergies between flux, remote sensing and modelling.
The global distribution of leaf chlorophyll content
Publisher: Elsevier BV
Date: 2020
Environmental controls on the spatial variability of savanna productivity in the Northern Territory, Australia
Publisher: Elsevier BV
Date: 11-2011
A Coupled Ground Heat Flux-Surface Energy Balance Model of Evaporation Using Thermal Remote Sensing Observations
Publisher: Copernicus GmbH
Date: 16-02-2022
DOI: 10.5194/BG-2021-356
Abstract: Abstract. The major undetermined problem in evaporation (ET) retrieval using thermal infrared (TIR) remote sensing is the lack of a physically based ground heat flux (G) model and its amalgamation with surface energy balance (SEB) model. Here, we present a novel approach based on coupling a thermal inertia (TI)-based mechanistic G model with an analytical SEB model (Surface Temperature Initiated Closure) (STIC, version STIC1.2). The coupled model is named as STIC-TI and it uses noon-night land surface temperature (TS), surface albedo and vegetation index from MODIS Aqua in conjunction with a clear-sky net radiation model and ancillary meteorological information. The SEB flux estimates from STIC-TI were evaluated with respect to the in-situ fluxes from Eddy Covariance (EC) measurements in erse agriculture and natural ecosystems of contrasting aridity in the northern hemisphere (e.g., India, United States of America) and southern hemisphere (e.g., Australia). Sensitivity analysis revealed substantial sensitivity of the STIC-TI derived fluxes due to TS uncertainty and partial compensation of sensitivity of G to TS due to the nature of the equations used in the TI-based G model. An evaluation of STIC-TI G estimates with respect to in-situ measurements showed an error range of 12–21 % across six flux tower sites in both the hemispheres. A comparison of STIC-TI G estimates with other G models revealed substantially better performance of the former. While the instantaneous noontime net radiation (RNi) and latent heat flux (LEi) was overestimated (15 % and 25 %), sensible heat flux (Hi) was underestimated with error of 22 %. The errors in Gi were associated with the errors in daytime TS and mismatch of footprint between the model estimates and measurements. Overestimation (underestimation) of LEi (Hi) was associated with the overestimation of net available energy (RNi – Gi) and use of unclosed SEB measurements. Being independent of any leaf-scale conductance parameterization and having a coupled sub-model of G, STIC-TI can make valuable contribution to map and monitor water stress and evaporation in the terrestrial ecosystems using noon-night thermal infrared observations from existing and future EO missions such as INSAT 4th generation and TRISHNA.
Impact of abrupt land cover changes by savanna fire on northern Australian climate
Publisher: American Geophysical Union (AGU)
Date: 10-10-2006
DOI: 10.1029/2005JD006860
A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas
Publisher: Copernicus GmbH
Date: 02-12-2015
DOI: 10.5194/BGD-12-18999-2015
Abstract: Abstract. Savanna ecosystems are one of the most dominant and complex terrestrial biomes that derives from a distinct vegetative surface comprised of co-dominant tree and grass populations. While these two vegetation types co-exist functionally, demographically they are not static, but are dynamically changing in response to environmental forces such as annual fire events and rainfall variability. Modelling savanna environments with the current generation of terrestrial biosphere models (TBMs) has presented many problems, particularly describing fire frequency and intensity, phenology, leaf biochemistry of C3 and C4 photosynthesis vegetation, and root water uptake. In order to better understand why TBMs perform so poorly in savannas, we conducted a model inter-comparison of 6 TBMs and assessed their performance at simulating latent energy (LE) and gross primary productivity (GPP) for five savanna sites along a rainfall gradient in northern Australia. Performance in predicting LE and GPP was measured using an empirical benchmarking system, which ranks models by their ability to utilise meteorological driving information to predict the fluxes. On average, the TBMs performed as well as a multi-linear regression of the fluxes against solar radiation, temperature and vapour pressure deficit, but were outperformed by a more complicated nonlinear response model that also included the leaf area index (LAI). This identified that the TBMs are not fully utilising their input information effectively in determining savanna LE and GPP, and highlights that savanna dynamics cannot be calibrated into models and that there are problems in underlying model processes. We identified key weaknesses in a model's ability to simulate savanna fluxes and their seasonal variation, related to the representation of vegetation by the models and root water uptake. We underline these weaknesses in terms of three critical areas for development. First, prescribed tree-rooting depths must be deep enough, enabling the extraction of deep soil water stores to maintain photosynthesis and transpiration during the dry season. Second, models must treat grasses as a co-dominant interface for water and carbon exchange, rather than a secondary one to trees. Third, models need a dynamic representation of LAI that encompasses the dynamic phenology of savanna vegetation and its response to rainfall interannual variability. We believe this study is the first to assess how well TBMs simulate savanna ecosystems, and that these results will be used to improve the representation of savannas ecosystems in future global climate model studies.
An introduction to the Australian and New Zealand flux tower network – OzFlux
Publisher: Copernicus GmbH
Date: 31-10-2016
Abstract: Abstract. OzFlux is the regional Australian and New Zealand flux tower network that aims to provide a continental-scale national research facility to monitor and assess trends, and improve predictions, of Australia's terrestrial biosphere and climate. This paper describes the evolution, design, and current status of OzFlux as well as provides an overview of data processing. We analyse measurements from all sites within the Australian portion of the OzFlux network and two sites from New Zealand. The response of the Australian biomes to climate was largely consistent with global studies except that Australian systems had a lower ecosystem water-use efficiency. Australian semi-arid/arid ecosystems are important because of their huge extent (70 %) and they have evolved with common moisture limitations. We also found that Australian ecosystems had a similar radiation-use efficiency per unit leaf area compared to global values that indicates a convergence toward a similar biochemical efficiency. The two New Zealand sites represented extremes in productivity for a moist temperate climate zone, with the grazed dairy farm site having the highest GPP of any OzFlux site (2620 gC m−2 yr−1) and the natural raised peat bog site having a very low GPP (820 gC m−2 yr−1). The paper discusses the utility of the flux data and the synergies between flux, remote sensing, and modelling. Lastly, the paper looks ahead at the future direction of the network and concludes that there has been a substantial contribution by OzFlux, and considerable opportunities remain to further advance our understanding of ecosystem response to disturbances, including drought, fire, land-use and land-cover change, land management, and climate change, which are relevant both nationally and internationally. It is suggested that a synergistic approach is required to address all of the spatial, ecological, human, and cultural challenges of managing the delicately balanced ecosystems in Australasia.
The use of a reduced form model to assess the sensitivity of a land surface model to biotic surface parameters
Publisher: Springer Science and Business Media LLC
Date: 08-2002
Stem and leaf gas exchange and their responses to fire in a north Australian tropical savanna
Publisher: Wiley
Date: 12-2005
DOI: 10.1111/J.1365-3040.2005.01442.X
Abstract: We measured stem CO2 efflux and leaf gas exchange in a tropical savanna ecosystem in northern Australia, and assessed the impact of fire on these processes. Gas exchange of mature leaves that flushed after a fire showed only slight differences from that of mature leaves on unburned trees. Expanding leaves typically showed net losses of CO2 to the atmosphere in both burned and unburned trees, even under saturating irradiance. Fire caused stem CO2 efflux to decline in overstory trees, when measured 8 weeks post-fire. This decline was thought to have resulted from reduced availability of C substrate for respiration, due to reduced canopy photosynthesis caused by leaf scorching, and to priority allocation of fixed C towards reconstruction of a new canopy. At the ecosystem scale, we estimated the annual above-ground woody-tissue CO2 efflux to be 275 g C m(-2) ground area year(-1) in a non-fire year, or approximately 13% of the annual gross primary production. We contrasted the canopy physiology of two co-dominant overstory tree species, one of which has a smooth bark on its branches capable of photosynthetic re-fixation (Eucalyptus miniata), and the other of which has a thick, rough bark incapable of re-fixation (Eucalyptus tetrodonta). Eucalyptus miniata supported a larger branch sapwood cross-sectional area in the crown per unit subtending leaf area, and had higher leaf stomatal conductance and photosynthesis than E. tetrodonta. Re-fixation by photosynthetic bark reduces the C cost of delivering water to evaporative sites in leaves, because it reduces the net C cost of constructing and maintaining sapwood. We suggest that re-fixation allowed leaves of E. miniata to photosynthesize at higher rates than those of E. tetrodonta, while the two invested similar amounts of C in the maintenance of branch sapwood.
Supplementary material to "MODIS vegetation products as proxies of photosynthetic potential: a look across meteorological and biologic driven ecosystem productivity"
Publisher: Copernicus GmbH
Date: 04-12-2015
Spatial patterns and temporal dynamics in savanna vegetation phenology across the north australian tropical transect
Publisher: Elsevier BV
Date: 12-2013
The role of aerodynamic resistance in thermal remote sensing-based evapotranspiration models
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-2186
Abstract: & & & #8216 Aerodynamic resistance& #8217 (hereafter r& sub& a& /sub& ) is a preeminent variable in the modelling of evapotranspiration (ET), and its accurate quantification plays a critical role in determining the performance and consistency of thermal remote sensing-based surface energy balance (SEB) models for estimating ET at local to regional scales. Atmospheric stability links r& sub& a& /sub& with land surface temperature (LST) and the representation of their interactions in the SEB models determines the accuracy of ET estimates.& & & & The present study investigates the influence of r& sub& a& /sub& and its relation to LST uncertainties on the performance of three structurally different SEB models by combining nine OzFlux eddy covariance datasets from 2011 to 2019 from sites of different aridity in Australia with MODIS Terra and Aqua LST and leaf area index (LAI) products. Simulations of the latent heat flux (LE, energy equivalent of ET in W/m& sup& & /sup& ) from the SPARSE (Soil Plant Atmosphere and Remote Sensing Evapotranspiration), SEBS (Surface Energy Balance System) and STIC (Surface Temperature Initiated Closure) models forced with MODIS LST, LAI, and in-situ meteorological datasets were evaluated using observed flux data across water-limited (semi-arid and arid) and radiation-limited (mesic) ecosystems.& & & & Our results revealed that the three models tend to overestimate instantaneous LE in the water-limited shrubland, woodland and grassland ecosystems by up to 60% on average, which was caused by an underestimation of the sensible heat flux (H). LE overestimation was associated with discrepancies in r& sub& a& /sub& retrievals under conditions of high atmospheric instability, during which errors in LST (expressed as the difference between MODIS LST and in-situ LST) apparently played a minor role. On the other hand, a positive bias in LST coincides with low r& sub& a& /sub& and causes slight underestimation of LE at the water-limited sites. The impact of r& sub& a& /sub& on the LE residual error was found to be of the same magnitude as the influence of errors in LST in the semi-arid ecosystems as indicated by variable importance in projection (VIP) coefficients from partial least squares regression above unity. In contrast, our results for mesic forest ecosystems indicated minor dependency on r& sub& a& /sub& for modelling LE (VIP& .4), which was due to a higher roughness length and lower LST resulting in dominance of mechanically generated turbulence, thereby diminishing the importance of atmospheric stability in the determination of r& sub& a& /sub& .& &
Termite sensitivity to temperature affects global wood decay rates
Publisher: American Association for the Advancement of Science (AAAS)
Date: 28-09-2022
Abstract: Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate change effects on wood carbon pools. Using data from 133 sites spanning six continents, we found that termite wood discovery and consumption were highly sensitive to temperature (with decay increasing .8 times per 10°C increase in temperature)—even more so than microbes. Termite decay effects were greatest in tropical seasonal forests, tropical savannas, and subtropical deserts. With tropicalization (i.e., warming shifts to tropical climates), termite wood decay will likely increase as termites access more of Earth’s surface.
An analysis of the surface energy budget above the world's tallest angiosperm forest
Publisher: Elsevier BV
Date: 12-2012
Community fire safety at the urban rural interface: the bushfire risk
Publisher: Elsevier BV
Date: 07-2000
An introduction to the Australian and New Zealand flux tower network – OzFlux
Publisher: Copernicus GmbH
Date: 28-04-2016
DOI: 10.5194/BG-2016-152
Abstract: Abstract. OzFlux is the regional Australian and New Zealand flux tower network that aims to provide a continental-scale national research facility to monitor and assess trends, and improve predictions, of Australia’s terrestrial biosphere and climate. This paper describes the evolution, design and current status of OzFlux as well as an overview of data processing. We analyse measurements from the Australian portion of the OzFlux network and found that the response of Australian biomes to climate was largely consistent with global studies but that Australian systems had a lower ecosystem water-use efficiency. Australian semi-arid/arid ecosystems are important because of their huge extent (70 %) and they have evolved with common moisture limitations. We also found that Australian ecosystems had similar radiation use efficiency per unit leaf area compared to global values that indicates a convergence toward a similar biochemical efficiency. The paper discusses the utility of the flux data and the synergies between flux, remote sensing and modelling. Lastly, the paper looks ahead at the future direction of the network and concludes that there has been a substantial contribution by OzFlux and considerable opportunities remain to further advance our understanding of ecosystem response to disturbances including drought, fire, land use and land cover change, land management and climate change that are relevant both nationally and internationally. It is suggested that a synergistic approach is required to address all of the spatial, ecological, human and cultural challenges of managing the delicately balanced ecosystems in Australia.
The influence of carbon costs and benefits on predicted vegetation behaviour along a precipitation gradient using the Vegetation Optimality Model
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-10740
Abstract: & & Vegetation properties such as rooting depths and vegetation cover play a key role in coupling ecological and hydrological processes. These properties are however highly variable in space and/or time and their parametrization generally poses challenges for terrestrial biosphere models (Whitley et al., 2016). Models often use static values for dynamic vegetation properties or prescribe values based on observations, such as remotely sensed leaf area index. Here, vegetation optimality provides a way forward in order to predict such vegetation properties and their response to environmental change (Schymanski et al., 2015).& & & & In this study, we explore the utility of a combined water-vegetation model, the Vegetation Optimality Model (VOM, Schymanski et al., 2009), to predict vegetation properties such as rooting depths, foliage cover, photosynthetic capacity and water use strategies. The VOM schematizes perennial trees and seasonal grasses each as a single big leaf with an associated root system and optimizes leaf and root system properties in order to maximize the Net Carbon Profit, i.e. the difference between the total carbon taken up by photosynthesis and all the carbon costs related to the construction and maintenance of the plant organs involved. The VOM was applied along the North-Australian Tropical Transect, which consists of six savanna sites equipped with flux towers along a strong rainfall gradient between 500 and 1700 mm per year. The multi-annual half-hourly measurements of evaporation and CO& sub& & /sub& -assimilation at the different sites were used here to evaluate the model.& & & & The VOM produced similar or better results than more traditional models even though it requires much less information about site-specific vegetation properties. However, we found a persistent bias in the predicted vegetation cover. More detailed numerical experiments revealed a likely misrepresentation of the foliage costs in the model, which are based on a linear relation between leaf area and fractional vegetation cover. This finding, and the already favourable comparison with traditional models, implies that optimization of vegetation properties for Net Carbon Profit is a very promising approach for predicting the soil-vegetation-atmosphere exchange of water and carbon in complex ecosystems such as savannas.& & & & & strong& References& br& & /strong& Schymanski, S.J., Roderick, M.L., Sivapalan, M., 2015. Using an optimality model to understand medium and long-term responses of vegetation water use to elevated atmospheric CO2 concentrations. AoB PLANTS 7, plv060. 0.1093/aobpla lv060& & & & Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality& #8208 based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. 0.1029/2008WR006841& & & & Whitley, R., Beringer, J., Hutley, L.B., Abramowitz, G., De Kauwe, M.G., Duursma, R., Evans, B., Haverd, V., Li, L., Ryu, Y., Smith, B., Wang, Y.-P., Williams, M., Yu, Q., 2016. A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas. Biogeosciences 13, 3245& #8211 . 0.5194/bg-13-3245-2016& &
Estimating and up-scaling fuel moisture and leaf dry matter content of a temperate humid forest using multi resolution remote sensing data
Publisher: MDPI AG
Date: 19-11-2016
DOI: 10.3390/RS8110961
Automated chamber system to measure field evapotranspiration rates
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2015
Structural complexity and land-surface energy exchange along a gradient from arctic tundra to boreal forest
Publisher: Wiley
Date: 24-02-2004
Solar‐induced chlorophyll fluorescence is strongly correlated with terrestrial photosynthesis for a wide variety of biomes: First global analysis based on OCO‐2 and flux tower observations
Publisher: Wiley
Date: 04-06-2018
DOI: 10.1111/GCB.14297
Abstract: Solar-induced chlorophyll fluorescence (SIF) has been increasingly used as a proxy for terrestrial gross primary productivity (GPP). Previous work mainly evaluated the relationship between satellite-observed SIF and gridded GPP products both based on coarse spatial resolutions. Finer resolution SIF (1.3 km × 2.25 km) measured from the Orbiting Carbon Observatory-2 (OCO-2) provides the first opportunity to examine the SIF-GPP relationship at the ecosystem scale using flux tower GPP data. However, it remains unclear how strong the relationship is for each biome and whether a robust, universal relationship exists across a variety of biomes. Here we conducted the first global analysis of the relationship between OCO-2 SIF and tower GPP for a total of 64 flux sites across the globe encompassing eight major biomes. OCO-2 SIF showed strong correlations with tower GPP at both midday and daily timescales, with the strongest relationship observed for daily SIF at the 757 nm (R
Insights Into the Aerodynamic Versus Radiometric Surface Temperature Debate in Thermal‐Based Evaporation Modeling
Publisher: American Geophysical Union (AGU)
Date: 08-08-2022
DOI: 10.1029/2021GL097568
Abstract: Global evaporation monitoring from Earth observation thermal infrared satellite missions is historically challenged due to the unavailability of any direct measurements of aerodynamic temperature. State‐of‐the‐art one‐source evaporation models use remotely sensed radiometric surface temperature as a substitute for the aerodynamic temperature and apply empirical corrections to accommodate for their inequality. This introduces substantial uncertainty in operational drought mapping over complex landscapes. By employing a non‐parametric model, we show that evaporation can be directly retrieved from thermal satellite data without the need of any empirical correction. Independent evaluation of evaporation in a broad spectrum of biome and aridity yielded statistically significant results when compared with eddy covariance observations. While our simplified model provides a new perspective to advance spatio‐temporal evaporation mapping from any thermal remote sensing mission, the direct retrieval of aerodynamic temperature also generates the highly required insight on the critical role of biophysical interactions in global evaporation research.
Temperature sensitivity of termites determines global wood decay rates
Publisher: Research Square Platform LLC
Date: 11-01-2022
DOI: 10.21203/RS.3.RS-1242094/V1
Abstract: Animals, such as termites, have largely been overlooked as global-scale drivers of biogeochemical cycles 1,2 , despite site-specific findings 3,4 . Deadwood turnover, an important component of the carbon cycle, is driven by multiple decay agents. Studies have focused on temperate systems 5,6 , where microbes dominate decay 7 . Microbial decay is sensitive to temperature, typically doubling per 10°C increase (decay effective Q 10 = ~2) 8–10 . Termites are important decayers in tropical systems 3,11–13 and differ from microbes in their population dynamics, dispersal, and substrate discovery 14–16 , meaning their climate sensitivities also differ. Using a network of 133 sites spanning 6 continents, we report the first global field-based quantification of temperature and precipitation sensitivities for termites and microbes, providing novel understandings of their response to changing climates. Temperature sensitivity of microbial decay was within previous estimates. Termite discovery and consumption were both much more sensitive to temperature (decay effective Q 10 = 6.53), leading to striking differences in deadwood turnover in areas with and without termites. Termite impacts were greatest in tropical seasonal forests and savannas and subtropical deserts. With tropicalization 17 (i.e., warming shifts to a tropical climate), the termite contribution to global wood decay will increase as more of the earth’s surface becomes accessible to termites.
Exploring the link between clouds, radiation, and canopy productivity of tropical savannas
Publisher: Elsevier BV
Date: 12-2013
A sub-continental scale living laboratory
Publisher: Elsevier BV
Date: 11-2011
Comment on enhancing the impact of the FLUXNET network of eddy covariance sites
Publisher: Copernicus GmbH
Date: 29-07-2020
Forests buffer thermal fluctuation better than non-forests
Publisher: Elsevier BV
Date: 07-2020
A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas
Publisher: Copernicus GmbH
Date: 03-06-2016
Abstract: Abstract. The savanna ecosystem is one of the most dominant and complex terrestrial biomes, deriving from a distinct vegetative surface comprised of co-dominant tree and grass populations. While these two vegetation types co-exist functionally, demographically they are not static but are dynamically changing in response to environmental forces such as annual fire events and rainfall variability. Modelling savanna environments with the current generation of terrestrial biosphere models (TBMs) has presented many problems, particularly describing fire frequency and intensity, phenology, leaf biochemistry of C3 and C4 photosynthesis vegetation, and root-water uptake. In order to better understand why TBMs perform so poorly in savannas, we conducted a model inter-comparison of six TBMs and assessed their performance at simulating latent energy (LE) and gross primary productivity (GPP) for five savanna sites along a rainfall gradient in northern Australia. Performance in predicting LE and GPP was measured using an empirical benchmarking system, which ranks models by their ability to utilise meteorological driving information to predict the fluxes. On average, the TBMs performed as well as a multi-linear regression of the fluxes against solar radiation, temperature and vapour pressure deficit but were outperformed by a more complicated nonlinear response model that also included the leaf area index (LAI). This identified that the TBMs are not fully utilising their input information effectively in determining savanna LE and GPP and highlights that savanna dynamics cannot be calibrated into models and that there are problems in underlying model processes. We identified key weaknesses in a model's ability to simulate savanna fluxes and their seasonal variation, related to the representation of vegetation by the models and root-water uptake. We underline these weaknesses in terms of three critical areas for development. First, prescribed tree-rooting depths must be deep enough, enabling the extraction of deep soil-water stores to maintain photosynthesis and transpiration during the dry season. Second, models must treat grasses as a co-dominant interface for water and carbon exchange rather than a secondary one to trees. Third, models need a dynamic representation of LAI that encompasses the dynamic phenology of savanna vegetation and its response to rainfall interannual variability. We believe that this study is the first to assess how well TBMs simulate savanna ecosystems and that these results will be used to improve the representation of savannas ecosystems in future global climate model studies.
Bridging Thermal Infrared Sensing and Physically‐Based Evapotranspiration Modeling: From Theoretical Implementation to Validation Across an Aridity Gradient in Australian Ecosystems
Publisher: American Geophysical Union (AGU)
Date: 05-2018
DOI: 10.1029/2017WR021357
Fire effects on net radiation and energy partitioning: Contrasting responses of tundra and boreal forest ecosystems
Publisher: American Geophysical Union (AGU)
Date: 05-05-2005
DOI: 10.1029/2004JD005299
Supplementary material to "A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas"
Publisher: Copernicus GmbH
Date: 02-12-2015
Carbon dioxide fluxes dominate the greenhouse gas exchanges of a seasonal wetland in the wet–dry tropics of northern Australia
Publisher: Elsevier BV
Date: 12-2013
Influence of savanna fire on Australian monsoon season precipitation and circulation as simulated using a distributed computing environment
Publisher: American Geophysical Union (AGU)
Date: 10-2007
DOI: 10.1029/2007GL030879
Disturbance and Climatic Drivers of Carbon Dynamics of a North Australian Tropical Savanna
Publisher: CRC Press
Date: 17-11-2010
DOI: 10.1201/B10275-6
Changing Urban climate and CO2 emissions: Implications for the development of policies for sustainable cities
Publisher: Informa UK Limited
Date: 03-2010
Vegetation type is an important predictor of the arctic summer land surface energy budget
Publisher: Springer Science and Business Media LLC
Date: 31-10-2022
DOI: 10.1038/S41467-022-34049-3
Abstract: Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994–2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm −2 ) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types.
Coupling carbon allocation with leaf and root phenology predicts tree–grass partitioning along a savanna rainfall gradient
Publisher: Copernicus GmbH
Date: 11-02-2016
Abstract: Abstract. The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree–grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximize long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for ex le, within the framework of a global biogeochemical model.We demonstrate the approach by encoding it in a new simple carbon–water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at five tower sites along the North Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area, and foliage projective cover along the NATT. The model behaviour emerges from complex feedbacks between the plant physiology and vegetation dynamics, mediated by shifting above- versus below-ground resources, and not from imposed hypotheses about the controls on tree–grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.
Retraction notice to 'Impacts of fire on forest age and runoff in mountain ash forests.' [Functional Plant Biology 35(2008), 483–492. doi:10.1071/FP08120]
Publisher: CSIRO Publishing
Date: 2010
Response to reviewers Describing rainfall in northern Australia using multiple climate indices
Publisher: Copernicus GmbH
Date: 03-10-2016
Evolution of maritime continent thunderstorms under varying meteorological conditions over The Tiwi Islands
Publisher: Wiley
Date: 2002
DOI: 10.1002/JOC.622
The representation of arctic soils in the land surface model: The importance of mosses
Publisher: American Meteorological Society
Date: 08-2001
Urban water storage capacity inferred from observed evapotranspiration recession 
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-2765
Abstract: & & The amount and dynamics of urban water storage play an important role in mitigating urban flooding and heat. Assessment of the capacity of cities to store water remains challenging due to the extreme heterogeneity of the urban surface. Evapotranspiration (ET) recession after rainfall events during the period without precipitation, over which the amount of stored water gradually decreases, can provide insight on the water storage capacity of urban surfaces. Assuming ET is the only outgoing flux, the water storage capacity can be estimated based on the timescale and intercept of its recession. In this paper, we test the proposed approach to estimate the water storage capacity at neighborhood scale with latent heat flux data collected by eddy covariance flux towers in eleven contrasting urban sites with different local climate zones, vegetation cover and characteristics and background climates (Amsterdam, Arnhem, Basel, Berlin, Helsinki, & #321 & #243 d& #378 , Melbourne, Mexico City, Seoul, Singapore, Vancouver). Water storage capacities ranging between 1 and 12 mm were found. These values correspond to e-folding timescales lasting from 2 to 10 days, which translate to half-lives of 1.5 to 7 days. We find ET at the start of a drydown to be positively related to vegetation fraction, and long timescales and large storage capacities to be associated with higher vegetation fractions. According to our results, urban water storage capacity is at least one order of magnitude smaller than the known water storage capacity in natural forests and grassland.& &
Phenology Dynamics of Dryland Ecosystems Along the North Australian Tropical Transect Revealed by Satellite Solar‐Induced Chlorophyll Fluorescence
Publisher: American Geophysical Union (AGU)
Date: 23-05-2019
DOI: 10.1029/2019GL082716
Modeling soil evaporation efficiency in a range of soil and atmospheric conditions using a meta‐analysis approach
Publisher: American Geophysical Union (AGU)
Date: 05-2016
DOI: 10.1002/2015WR018233
Control of atmospheric particles on diffuse radiation and terrestrial plant productivity
Publisher: SAGE Publications
Date: 14-02-2012
Is there more soil carbon under nitrogen-fixing trees than under non-nitrogen-fixing trees in mixed-species restoration plantings?
Publisher: Elsevier BV
Date: 04-2014
Evaluation of the remote-sensing-based DIFFUSE model for estimating photosynthesis of vegetation
Publisher: Elsevier BV
Date: 12-2014
Savanna fires and their impact on net ecosystem productivity in North Australia
Publisher: Wiley
Date: 14-03-2007
Soil carbon density can increase when Australian savanna is converted to pasture, but may not change under intense cropping systems
Publisher: Elsevier BV
Date: 10-2021
Influence of modifications (from AoB2015 to v0.5) in the Vegetation Optimality Model
Publisher: Copernicus GmbH
Date: 02-2022
Abstract: Abstract. The Vegetation Optimality Model (VOM, Schymanski et al., 2009, 2015) is an optimality-based, coupled water–vegetation model that predicts vegetation properties and behaviour based on optimality theory rather than calibrating vegetation properties or prescribing them based on observations, as most conventional models do. Several updates to previous applications of the VOM have been made for the study in the accompanying paper of Nijzink et al. (2022), where we assess whether optimality theory can alleviate common shortcomings of conventional models, as identified in a previous model inter-comparison study along the North Australian Tropical Transect (NATT, Whitley et al., 2016). Therefore, we assess in this technical paper how the updates to the model and input data would have affected the original results of Schymanski et al. (2015), and we implemented these changes one at a time. The model updates included extended input data, the use of variable atmospheric CO2 levels, modified soil properties, implementation of free drainage conditions, and the addition of grass rooting depths to the optimized vegetation properties. A systematic assessment of these changes was carried out by adding each in idual modification to the original version of the VOM at the flux tower site of Howard Springs, Australia. The analysis revealed that the implemented changes affected the simulation of mean annual evapotranspiration (ET) and gross primary productivity (GPP) by no more than 20 %, with the largest effects caused by the newly imposed free drainage conditions and modified soil texture. Free drainage conditions led to an underestimation of ET and GPP in comparison with the results of Schymanski et al. (2015), whereas more fine-grained soil textures increased the water storage in the soil and resulted in increased GPP. Although part of the effect of free drainage was compensated for by the updated soil texture, when combining all changes, the resulting effect on the simulated fluxes was still dominated by the effect of implementing free drainage conditions. Eventually, the relative error for the mean annual ET, in comparison with flux tower observations, changed from an 8.4 % overestimation to an 10.2 % underestimation, whereas the relative errors for the mean annual GPP remained similar, with an overestimation that slightly reduced from 17.8 % to 14.7 %. The sensitivity to free drainage conditions suggests that a realistic representation of groundwater dynamics is very important for predicting ET and GPP at a tropical open-forest savanna site as investigated here. The modest changes in model outputs highlighted the robustness of the optimization approach that is central to the VOM architecture.
Land use change and the impact on greenhouse gas exchange in north Australian savanna soils
Publisher: Copernicus GmbH
Date: 25-01-2012
Abstract: Abstract. Savanna ecosystems are subjected to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) over a complete wet-dry seasonal cycle at three replicate sites of each of three land uses: savanna, young pasture and old pasture (converted from savanna 5–7 and 25–30 yr ago, respectively) in the Douglas Daly region of Northern Australia. The effect of break of season rains at the end of the dry season was investigated with two irrigation experiments. Land use change from savanna to pasture increased net greenhouse gas fluxes from the soil. Pasture sites were a weaker sink for CH4 than savanna sites and, under wet conditions, old pastures turned from being sinks to a significant source of CH4. Nitrous oxide emissions were generally very low, in the range of 0 to 5 μg N2O-N m−2 h−1, and under dry conditions soil uptake of N2O was apparent. Break of season rains produced a small, short lived pulse of N2O up to 20 μg N2O-N m−2 h−1, most evident in pasture soil. Annual cumulative soil CO2 fluxes increased after clearing, with savanna (14.6 t CO2-C ha−1 yr−1) having the lowest fluxes compared to old pasture (18.5 t CO2-C ha−1 yr−1) and young pasture (20.0 t CO2-C ha−1 yr−1). Clearing savanna increased soil-based greenhouse gas emissions from 53 to ∼ 70 t CO2-equivalents, a 30% increase dominated by an increase in soil CO2 emissions and shift from soil CH4 sink to source. Seasonal variation was clearly driven by soil water content, supporting the emerging view that soil water content is a more important driver of soil gas fluxes than soil temperature in tropical ecosystems where temperature varies little among seasons.
Estimating nocturnal ecosystem respiration from the vertical turbulent flux and change in storage of CO2
Publisher: Elsevier BV
Date: 11-2009
Biomass burning and resulting emissions in the northern territory, australia
Publisher: CSIRO Publishing
Date: 1995
DOI: 10.1071/WF9950229
Abstract: The extent of biomass burning in the Northern Territory, Australia, during 1992 (a year of low fire activity) was estimated using NOAA-AVHRR satellite imagery and was subsequently used to calculate the emission of gaseous compounds from biomass burning for that year. A total of 73,729 km2 was determined to have been burnt, representing 5.5% of the total Northern Territory area. The extent of biomass burning in different vegetation units in the Northern Territory was also estimated with eucalypt communities comprising 72% of the total area burnt. An estimated 29.5 x 106 tonnes of biomass was consumed by burning, resulting in the production of an estimated : 1. 11.3 Tg C as carbon dioxide, 2. 1.02 Tg C as carbon monoxide, (3) 5.23 x 10-3 Tg C as total particulate matter, 4. 26.1 x 10-3 Tg N as nitrous oxides, 5. various other trace gases. The calculated release of CO2 in this study accounts for only 41% of the estimated Australian contribution to global emmissions from biomass burning, indicating that the Australian contribution may be overestimted.
Tree–grass phenology information improves light use efficiency modelling of gross primary productivity for an Australian tropical savanna
Publisher: Copernicus GmbH
Date: 10-01-2017
Abstract: Abstract. The coexistence of trees and grasses in savanna ecosystems results in marked phenological dynamics that vary spatially and temporally with climate. Australian savannas comprise a complex variety of life forms and phenologies, from evergreen trees to annual erennial grasses, producing a boom–bust seasonal pattern of productivity that follows the wet–dry seasonal rainfall cycle. As the climate changes into the 21st century, modification to rainfall and temperature regimes in savannas is highly likely. There is a need to link phenology cycles of different species with productivity to understand how the tree–grass relationship may shift in response to climate change. This study investigated the relationship between productivity and phenology for trees and grasses in an Australian tropical savanna. Productivity, estimated from overstory (tree) and understory (grass) eddy covariance flux tower estimates of gross primary productivity (GPP), was compared against 2 years of repeat time-lapse digital photography (phenocams). We explored the phenology–productivity relationship at the ecosystem scale using Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices and flux tower GPP. These data were obtained from the Howard Springs OzFlux/Fluxnet site (AU-How) in northern Australia. Two greenness indices were calculated from the phenocam images: the green chromatic coordinate (GCC) and excess green index (ExG). These indices captured the temporal dynamics of the understory (grass) and overstory (trees) phenology and were correlated well with tower GPP for understory (r2 = 0.65 to 0.72) but less so for the overstory (r2 = 0.14 to 0.23). The MODIS enhanced vegetation index (EVI) correlated well with GPP at the ecosystem scale (r2 = 0.70). Lastly, we used GCC and EVI to parameterise a light use efficiency (LUE) model and found it to improve the estimates of GPP for the overstory, understory and ecosystem. We conclude that phenology is an important parameter to consider in estimating GPP from LUE models in savannas and that phenocams can provide important insights into the phenological variability of trees and grasses.
MODIS vegetation products as proxies of photosynthetic potential along a gradient of meteorologically and biologically driven ecosystem productivity
Publisher: Copernicus GmbH
Date: 07-10-2016
Abstract: Abstract. A direct relationship between gross ecosystem productivity (GEP) estimated by the eddy covariance (EC) method and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices (VIs) has been observed in many temperate and tropical ecosystems. However, in Australian evergreen forests, and particularly sclerophyll and temperate woodlands, MODIS VIs do not capture seasonality of GEP. In this study, we re-evaluate the connection between satellite and flux tower data at four contrasting Australian ecosystems, through comparisons of GEP and four measures of photosynthetic potential, derived via parameterization of the light response curve: ecosystem light use efficiency (LUE), photosynthetic capacity (Pc), GEP at saturation (GEPsat), and quantum yield (α), with MODIS vegetation satellite products, including VIs, gross primary productivity (GPPMOD), leaf area index (LAIMOD), and fraction of photosynthetic active radiation (fPARMOD). We found that satellite-derived biophysical products constitute a measurement of ecosystem structure (e.g. leaf area index – quantity of leaves) and function (e.g. leaf level photosynthetic assimilation capacity – quality of leaves), rather than GEP. Our results show that in primarily meteorological-driven (e.g. photosynthetic active radiation, air temperature, and/or precipitation) and relatively aseasonal ecosystems (e.g. evergreen wet sclerophyll forests), there were no statistically significant relationships between GEP and satellite-derived measures of greenness. In contrast, for phenology-driven ecosystems (e.g. tropical savannas), changes in the vegetation status drove GEP, and tower-based measurements of photosynthetic activity were best represented by VIs. We observed the highest correlations between MODIS products and GEP in locations where key meteorological variables and vegetation phenology were synchronous (e.g. semi-arid Acacia woodlands) and low correlation at locations where they were asynchronous (e.g. Mediterranean ecosystems). However, we found a statistical significant relationship between the seasonal measures of photosynthetic potential (Pc and LUE) and VIs, where each ecosystem aligns along a continuum we emphasize here that knowledge of the conditions in which flux tower measurements and VIs or other remote sensing products converge greatly advances our understanding of the mechanisms driving the carbon cycle (phenology and climate drivers) and provides an ecological basis for interpretation of satellite-derived measures of greenness.
Consequences of altered temperature regimes for emerging freshwater invertebrates
Publisher: Springer Science and Business Media LLC
Date: 17-06-2016
Inferring CO2 fertilization effect based on global monitoring land-atmosphere exchange with a theoretical model
Publisher: IOP Publishing
Date: 17-07-2020
Abstract: Rising atmospheric CO 2 concentration ([CO 2 ]) enhances photosynthesis and reduces transpiration at the leaf, ecosystem, and global scale via the CO 2 fertilization effect. The CO 2 fertilization effect is among the most important processes for predicting the terrestrial carbon budget and future climate, yet it has been elusive to quantify. For evaluating the CO 2 fertilization effect on land photosynthesis and transpiration, we developed a technique that isolated this effect from other confounding effects, such as changes in climate, using a noisy time series of observed land-atmosphere CO 2 and water vapor exchange. Here, we evaluate the magnitude of this effect from 2000 to 2014 globally based on constraint optimization of gross primary productivity (GPP) and evapotranspiration in a canopy photosynthesis model over 104 global eddy-covariance stations. We found a consistent increase of GPP (0.138 ± 0.007% ppm −1 percentile per rising ppm of [CO 2 ]) and a concomitant decrease in transpiration (−0.073% ± 0.006% ppm −1 ) due to rising [CO 2 ]. Enhanced GPP from CO 2 fertilization after the baseline year 2000 is, on average, 1.2% of global GPP, 12.4 g C m −2 yr −1 or 1.8 Pg C yr −1 at the years from 2001 to 2014. Our result demonstrates that the current increase in [CO 2 ] could potentially explain the recent land CO 2 sink at the global scale.
Aerosols and their influence on radiation partitioning and savanna productivity in northern Australia
Publisher: Springer Science and Business Media LLC
Date: 23-08-2010
A canopy‐scale test of the optimal water‐use hypothesis
Publisher: Wiley
Date: 04-10-2007
DOI: 10.1111/J.1365-3040.2007.01740.X
Abstract: Common empirical models of stomatal conductivity often incorporate a sensitivity of stomata to the rate of leaf photosynthesis. Such a sensitivity has been predicted on theoretical terms by Cowan and Farquhar, who postulated that stomata should adjust dynamically to maximize photosynthesis for a given water loss. In this study, we implemented the Cowan and Farquhar hypothesis of optimal stomatal conductivity into a canopy gas exchange model, and predicted the diurnal and daily variability of transpiration for a savanna site in the wet-dry tropics of northern Australia. The predicted transpiration dynamics were then compared with observations at the site using the eddy covariance technique. The observations were also used to evaluate two alternative approaches: constant conductivity and a tuned empirical model. The model based on the optimal water-use hypothesis performed better than the one based on constant stomatal conductivity, and at least as well as the tuned empirical model. This suggests that the optimal water-use hypothesis is useful for modelling canopy gas exchange, and that it can reduce the need for model parameterization.
Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northern Australia
Publisher: CSIRO Publishing
Date: 2003
DOI: 10.1071/WF03023
Abstract: Savannas form a large fraction of the total tropical vegetation and are extremely fire prone. We measured radiative, energy and carbon exchanges over unburned and burned (both before and after low and moderate intensity fires) open forest savanna at Howard Springs, Darwin, Australia. Fire affected the radiative balance immediately following fire through the consumption of the grass-dominated understorey and blackening of the surface. Albedo was halved following fire of both intensities (from 0.12 to 0.07 and from 0.11 to 0.06 for the moderate and low intensity sites, respectively), but the recovery of albedo was dependent on the initial fire intensity. The low intensity fire caused little canopy damage with little impact on the surface energy balance and only a slight increase in Bowen ratio. However the moderate fire resulted in a comprehensive canopy scorch and almost complete leaf drop in the weeks following fire. The shutdown of most leaves within the canopy reduced transpiration and altered energy partitioning. Leaf death and shedding also resulted in a cessation of ecosystem carbon uptake and the savanna turned from a sink to a source of carbon to the atmosphere because of the continued ecosystem respiration. Post-fire, the Bowen ratio increased greatly due to large increases in sensible heat fluxes. These changes in surface energy exchange following fire, when applied at the landscape scale, may have impacts on climate through local changes in circulation patterns and changes in regional heating, precipitation and monsoon circulation.
Urban Water Storage Capacity Inferred From Observed Evapotranspiration Recession
Publisher: American Geophysical Union (AGU)
Date: 08-02-2022
DOI: 10.1029/2021GL096069
Abstract: Water storage plays an important role in mitigating heat and flooding in urban areas. Assessment of the water storage capacity of cities remains challenging due to the inherent heterogeneity of the urban surface. Traditionally, effective storage has been estimated from runoff. Here, we present a novel approach to estimate effective water storage capacity from recession rates of observed evaporation during precipitation‐free periods. We test this approach for cities at neighborhood scale with eddy‐covariance based latent heat flux observations from 14 contrasting sites with different local climate zones, vegetation cover and characteristics, and climates. Based on analysis of 583 drydowns, we find storage capacities to vary between 1.3 and 28.4 mm, corresponding to e ‐folding timescales of 1.8–20.1 days. This makes the urban storage capacity at least five times smaller than all the observed values for natural ecosystems, reflecting an evaporation regime characterized by extreme water limitation.
Carbon cycling in a mountain ash forest: Analysis of below ground respiration
Publisher: Elsevier BV
Date: 11-2007
Effects of wetting frequency and afforestation on carbon, nitrogen and the microbial community in soil
Publisher: Elsevier BV
Date: 09-2016
Local boundary-layer development over burnt and unburnt tropical savanna: an observational study
Publisher: Springer Science and Business Media LLC
Date: 19-06-2007
Estimation of latent heat flux over savannah vegetation across the North Australian Tropical Transect from multiple sensors and global meteorological data
Publisher: Elsevier BV
Date: 2017
Climate change and long‐term fire management impacts on A ustralian savannas
Publisher: Wiley
Date: 12-11-2014
DOI: 10.1111/NPH.13130
Abstract: Tropical savannas cover a large proportion of the Earth's land surface and many people are dependent on the ecosystem services that savannas supply. Their sustainable management is crucial. Owing to the complexity of savanna vegetation dynamics, climate change and land use impacts on savannas are highly uncertain. We used a dynamic vegetation model, the adaptive dynamic global vegetation model ( aDGVM ), to project how climate change and fire management might influence future vegetation in northern Australian savannas. Under future climate conditions, vegetation can store more carbon than under ambient conditions. Changes in rainfall seasonality influence future carbon storage but do not turn vegetation into a carbon source, suggesting that CO 2 fertilization is the main driver of vegetation change. The application of prescribed fires with varying return intervals and burning season influences vegetation and fire impacts. Carbon sequestration is maximized with early dry season fires and long fire return intervals, while grass productivity is maximized with late dry season fires and intermediate fire return intervals. The study has implications for management policy across Australian savannas because it identifies how fire management strategies may influence grazing yield, carbon sequestration and greenhouse gas emissions. This knowledge is crucial to maintaining important ecosystem services of Australian savannas.
Intrinsic climate dependency of ecosystem light and water-use-efficiencies across Australian biomes
Publisher: IOP Publishing
Date: 10-2014
Effect of environmental conditions on the relationship between solar‐induced fluorescence and gross primary productivity at an OzFlux grassland site
Publisher: American Geophysical Union (AGU)
Date: 03-2017
DOI: 10.1002/2016JG003580
Upscaling latent heat flux for thermal remote sensing studies: Comparison of alternative approaches and correction of bias
Publisher: Elsevier BV
Date: 10-2012
Integration of MODIS land and atmosphere products with a coupled-process model to estimate gross primary productivity and evapotranspiration from 1 km to global scales
Publisher: American Geophysical Union (AGU)
Date: 12-2011
DOI: 10.1029/2011GB004053
Temperature influences species interactions between a native and a globally invasive freshwater snail
Publisher: University of Chicago Press
Date: 09-2015
DOI: 10.1086/681639
Spatiotemporal partitioning of savanna plant functional type productivity along NATT
Publisher: Elsevier BV
Date: 09-2020
The contribution of trees and grasses to productivity of an Australian tropical savanna
Publisher: Copernicus GmbH
Date: 07-12-2015
DOI: 10.5194/BGD-12-19307-2015
Abstract: Abstract. Savanna ecosystems cover 20 % of the global land surface and account for 25 % of global terrestrial carbon uptake. They support one fifth of the world's human population and are one of the most important ecosystems on our planet. Savanna productivity is a product of the interplay between trees and grass that co-dominate savanna landscapes and are maintained through interactions with climate and disturbance (fire, land use change, herbivory). In this study, we evaluate the temporally dynamic partitioning of overstory and understory carbon dioxide fluxes in Australian tropical savanna using overstory and understory eddy covariance measurements. Over a two year period (September 2012 to October 2014) the overall net ecosystem productivity (NEP) of the savanna was 506.2 (±22 SE) g C m−2 yr−1. The total gross primary productivity (GPP) was 2267.1 (±80 SE) g C m−2 yr−1, of which the understory contributed 32 %. The understory contribution was strongly seasonal, with most GPP occurring in the wet season (40 % of total ecosystem in the wet season and 18 % in the dry). This study is the first to elucidate the temporal dynamics of savanna understory and overstory carbon flux components explicitly using observational information. Understanding grass productivity is crucial for evaluating fuel loads, as is tree productivity for quantifying the tree carbon sink. This information will contribute to a significant refinement of the representation of savannas in models, as well as improved understanding of relative tree-grass productivity and competition for resources.
Challenges and opportunities in modelling savanna ecosystems
Publisher: Copernicus GmbH
Date: 11-05-2016
DOI: 10.5194/BG-2016-190
Abstract: Abstract. The savanna complex is a highly erse global biome that occurs within the seasonally dry tropical to sub-tropical equatorial latitudes. Savannas are open-canopy environments that encompass a broad demographic continuum, often characterised by a dynamically changing dominance between C3-tree and C4-grass vegetation, where frequent environmental disturbances such as fire modulates the balance between ephemeral and perennial life forms. Climate change is projected to result in significant changes to the savanna floristic structure, with increases to woody biomass expected through CO2 fertilisation in mesic savannas and increased tree mortality expected through increased rainfall interannual variability in xeric savannas. The complex interaction between vegetation and climate that occurs in savannas has traditionally challenged current-generation terrestrial biosphere models (TBMs), which aim to simulate the interaction between the atmosphere and the land-surface to predict responses of vegetation to changing in environmental forcing. In this review, we examine whether TBMs are able to adequately represent savanna dynamics and what implications potential deficiencies may have for climate change projection scenarios that rely on these models. We start by highlighting the defining characteristic traits and behaviours of savanna, how these differ across continents, and how this information is (or is not) represented in the structural framework of many TBMs. We highlight three dynamic processes that we believe directly affect the water-use and productivity of the savanna system, namely: phenology root-water access and fire dynamics. Following this, we discuss how these processes are represented in many current generation TBMs and whether they are suitable for simulating savanna dynamics. Finally, we give an overview of how eddy-covariance observations in combination with other data sources, can be used in model benchmarking and inter-comparison frameworks to diagnose the performance of TBMs in this environment and formulate roadmaps for future development. Our investigation reveals that many TBMs systematically misrepresent phenology, effects of fire and root-water access (if they are considered at all) and that these should be critical areas for future development. Furthermore, such processes must not be static (i.e. prescribed behaviour), but be capable of responding to the changing environmental conditions in order to emulate the dynamic behaviour of savannas. Without such developments, however, TBMs will have limited predictive capability in making the critical projections needed to understand how savannas will respond to future global change.
Net ecosystem carbon exchange of a dry temperate eucalypt forest
Publisher: Copernicus GmbH
Date: 13-05-2016
DOI: 10.5194/BG-2016-192
Abstract: Abstract. Forest ecosystems play a crucial role in the global carbon cycle by sequestering a considerable fraction of anthropogenic CO2 thereby contributing to climate change mitigation. However, there is a gap in our understanding about the carbon dynamics of eucalypt (broadleaf evergreen) forests in temperate climates, which might differ from temperate coniferous or deciduous forests given their fundamental differences in physiology, phenology and growth dynamics. To address this gap we undertook a three year study (2010–2012) using eddy covariance measurements in a dry temperate eucalypt forest in south-eastern Australia. We determined the annual net ecosystem carbon exchange (NEE) and investigated the temporal (seasonal and inter-annual) variability and environmental controls of NEE, gross primary productivity (GPP) and ecosystem respiration (ER). The forest was a large and constant carbon sink throughout the study period, even in winter, with an overall mean NEE of −1062 ± 53 g C m−2 yr−1. Gross CO2 ecosystem fluxes showed no significant inter-annual variability and mean annual estimate of GPP was 2521 ± 35 g C m−2 yr−1 and ER was 1458 ± 31 g C m−2 yr−1. GPP and ER had a pronounced seasonality with GPP being greatest during spring and summer and ER during summer whereas peaks of NEE occurred in early spring and again in summer. High NEE in spring was caused by a delayed increase in ER due to low temperatures. A random forest analysis showed that variability in GPP was mostly explained by incoming solar radiation whilst air temperature was the main environmental driver of ER on seasonal and inter-annual time scales. The forest experienced unusual above average annual rainfall during the first two years of this three year period so that soil moisture content remained relatively high and the forest was not water limited. Our results show the potential of temperate eucalypt forests to sequester large amounts of carbon when not water limited. Our observations can provide data on an underrepresented biome to test and parameterise ecosystem models. However, longer monitoring is needed to assess the inter-annual variability of the carbon sink strength particularly during years with drought conditions.
Quantifying the relative importance of greenhouse gas emissions from current and future savanna land use change across northern Australia
Publisher: Copernicus GmbH
Date: 19-05-2016
DOI: 10.5194/BG-2016-191
Abstract: Abstract. Clearing and burning of tropical savanna leads to globally significant emissions of greenhouse gases (GHG) although there is large uncertainty relating to the magnitude of this flux. Australia’s tropical savannas occupy over 25 % of the continental land mass and have a potential to significant influence the national greenhouse gas budget, particularly because they are the focus of likely agricultural expansion. To investigate the role of deforestation on GHG emissions, a paired site approach was used. The CO2 exchange was measured from two tropical savanna woodland sites, one that was cleared, and a second analogue site that remained uncleared for a 22 month observation period. At both sites, net ecosystem exchange (NEE) was measured using the eddy covariance (EC) method. Observations at the cleared site was continuous before, during and after the clearing event, providing high resolution data that tracked CO2 emissions through multiple phases of land use change. At the cleared site, post-clearing debris was allowed to cure for 6 months and was subsequently burnt, followed by extensive soil preparation for cropping. Emissions were estimated from the debris fire by quantify the on-site biomass prior to clearing and applying savanna-specific emissions factors to estimate a fire-derived GHG emission. This was added to net CO2 fluxes as measured by the eddy covariance tower giving a total GHG emission of 154 Mg CO2-e ha−1 from a savanna woodland with a total fuel load (above- and below- ground woody debris, course woody debris, litter plus C4 grass fuel) of 40.9 Mg C ha−1. This emission was dominated by debris combustion from the fire event, which was 83 % of the total emission, the remained from soil emissions and decay of debris during the curing period prior to burning. Soil disturbance from ploughing and site preparation for cropping was responsible for almost 10 % of the total emission. Fluxes at the uncleared site were tracked using an additional flux tower for 668 days and over this period, cumulative NEE was −2.1 Mg C ha−1, a net carbon sink. Estimated emissions for this savanna type were then upscaled to provide estimates of the magnitude of emissions from any future deforestation. At current rates of deforestation, savanna burning is as significant a source of GHG emissions as deforestation, with fire emissions occurring every year across this savanna biome. However, expanded deforestation could exceed fire emissions and a clearing scenario was examined which suggested clearing over and above current rates could add up to 5 % to Australia’s national GHG account, depending on the annual rate of deforestation. This bottom-up study provides data that can reduce uncertainty associated with land use change for this extensive tropical ecosystem and provide an assessment of the relative magnitude of GHG emissions from savanna burning and deforestation as well as informing northern land use decision making processes.
Describing rainfall in northern Australia using multiple climate indices
Publisher: Copernicus GmbH
Date: 07-02-2017
Abstract: Abstract. Savanna landscapes are globally extensive and highly sensitive to climate change, yet the physical processes and climate phenomena which affect them remain poorly understood and therefore poorly represented in climate models. Both human populations and natural ecosystems are highly susceptible to precipitation variation in these regions due to the effects on water and food availability and atmosphere–biosphere energy fluxes. Here we quantify the relationship between climate phenomena and historical rainfall variability in Australian savannas and, in particular, how these relationships changed across a strong rainfall gradient, namely the North Australian Tropical Transect (NATT). Climate phenomena were described by 16 relevant climate indices and correlated against precipitation from 1900 to 2010 to determine the relative importance of each climate index on seasonal, annual and decadal timescales. Precipitation trends, climate index trends and wet season characteristics have also been investigated using linear statistical methods. In general, climate index–rainfall correlations were stronger in the north of the NATT where annual rainfall variability was lower and a high proportion of rainfall fell during the wet season. This is consistent with a decreased influence of the Indian–Australian monsoon from the north to the south. Seasonal variation was most strongly correlated with the Australian Monsoon Index, whereas yearly variability was related to a greater number of climate indices, predominately the Tasman Sea and Indonesian sea surface temperature indices (both of which experienced a linear increase over the duration of the study) and the El Niño–Southern Oscillation indices. These findings highlight the importance of understanding the climatic processes driving variability and, subsequently, the importance of understanding the relationships between rainfall and climatic phenomena in the Northern Territory in order to project future rainfall patterns in the region.
Responses of LAI to rainfall explain contrasting sensitivities to carbon uptake between forest and non-forest ecosystems in Australia
Publisher: Springer Science and Business Media LLC
Date: 15-09-2017
DOI: 10.1038/S41598-017-11063-W
Abstract: Non-forest ecosystems (predominant in semi-arid and arid regions) contribute significantly to the increasing trend and interannual variation of land carbon uptake over the last three decades, yet the mechanisms are poorly understood. By analysing the flux measurements from 23 ecosystems in Australia, we found the the correlation between gross primary production (GPP) and ecosystem respiration (R e ) was significant for non-forest ecosystems, but was not for forests. In non-forest ecosystems, both GPP and R e increased with rainfall, and, consequently net ecosystem production (NEP) increased with rainfall. In forest ecosystems, GPP and R e were insensitive to rainfall. Furthermore sensitivity of GPP to rainfall was dominated by the rainfall-driven variation of LAI rather GPP per unit LAI in non-forest ecosystems, which was not correctly reproduced by current land models, indicating that the mechanisms underlying the response of LAI to rainfall should be targeted for future model development.
Using long‐term water balances to parameterize surface conductances and calculate evaporation at 0.05° spatial resolution
Publisher: American Geophysical Union (AGU)
Date: 05-2010
DOI: 10.1029/2009WR008716
The comparative role of key environmental factors in determining savanna productivity and carbon fluxes: A review, with special reference to northern Australia
Publisher: SAGE Publications
Date: 28-04-2010
Abstract: Terrestrial ecosystems are highly responsive to their local environments and, as such, the rate of carbon uptake both in shorter and longer timescales and different spatial scales depends on local environmental drivers. For savannas, the key environmental drivers controlling vegetation productivity are water and nutrient availability, vapour pressure deficit (VPD), solar radiation and fire. Changes in these environmental factors can modify the carbon balance of these ecosystems. Therefore, understanding the environmental drivers responsible for the patterns (temporal and spatial) and processes (photosynthesis and respiration) has become a central goal in terrestrial carbon cycle studies. Here we have reviewed the various environmental controls on the spatial and temporal patterns on savanna carbon fluxes in northern Australia. Such studies are critical in predicting the impacts of future climate change on savanna productivity and carbon storage.
Assessing practical measures to reduce urban heat: Green and cool roofs
Publisher: Elsevier BV
Date: 12-2013
Carbon uptake and water use in woodlands and forests in southern Australia during an extreme heat wave event in the ‘Angry Summer’ of 2012/2013
Publisher: Copernicus GmbH
Date: 03-06-2016
DOI: 10.5194/BG-2016-183
Abstract: Abstract. As a result of climate change warmer temperatures are projected through the 21st century and are already increasing above modelled predictions. Apart from increases in the mean, warm/hot temperature extremes are expected to become more prevalent in the future, along with an increase in the frequency of droughts. It is crucial to better understand the response of terrestrial ecosystems to such temperature extremes for predicting land-surface feedbacks in a changing climate. During the 2012/2013 summer, Australia experienced a record-breaking heat wave with an exceptional spatial extent that lasted for several weeks. We synthesized eddy-covariance measurements from seven woodland and forest sites across climate zones in southern Australia, which we combined with model simulations from the CABLE land surface model to investigate the effect of this summer heat wave on the carbon and water exchange of terrestrial ecosystems. We found that the water-limited woodlands and the energy-limited forest ecosystem responded differently to the heat wave. During the most intense part of the heat wave, the woodlands experienced decreased latent heat flux, an increased Bowen ratio and a reduced carbon uptake while the forest ecosystem had increased latent heat flux, reduced Bowen ratio and increased carbon uptake. Ecosystem respiration was increased at all sites resulting in reduced net ecosystem productivity in the woodlands and constant net ecosystem productivity in the forest. Importantly all ecosystems remained carbon sinks during the event. Precipitation after the most intense first part of the heat wave and slightly cooler temperatures led to a decrease of the Bowen ratio and hence increased evaporative cooling. Carbon uptake in the woodlands also recovered quickly but respiration remained high. While woodlands and forest proved relatively resistant to this short-term heat extreme these carbon sinks may not sustainable in a future with an increased number, intensity and duration of heat waves.
Narrowband spectral indices for the estimation of chlorophyl along a precipitation gradient
Publisher: IEEE
Date: 06-2011
Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site
Publisher: Copernicus GmbH
Date: 17-06-2016
DOI: 10.5194/BG-2016-184
Abstract: Abstract. While the eddy covariance technique has become an important technique for estimating long-term ecosystem carbon balance, under certain conditions the measured turbulent flux of carbon at a given height above an ecosystem does not represent the true surface flux. Profile systems have been deployed to measure periodic storage of carbon below the measurement height, but have not been widely adopted. This is most likely due to the additional expense and complexity, and possibly also the perception – given that net storage over intervals exceeding 24 hours is generally negligible – that these measurements are not particularly important. In this study, we used a three year record of net ecosystem exchange of carbon and simultaneous measurements of carbon storage to ascertain the relative contributions of turbulent carbon flux, storage and advection (calculated as a residual quantity) to the nocturnal carbon balance, and to quantify the effect of neglecting storage. The conditions at the site are in relative terms highly favourable for eddy covariance measurements, yet we found a substantial contribution (~ 40 %) of advection to nocturnal turbulent flux underestimation. The most likely mechanism for advection is cooling-induced drainage flows, the effects of which were observed in the storage measurements. The remaining ~ 60 % of flux underestimation was due to storage of carbon. We also showed that substantial underestimation of carbon uptake (approximately 80 gC m−2 a−1, or 25 % of annual carbon uptake) arose when standard methods of nocturnal flux correction were implemented in the absence of storage estimates. These biases were much larger than quantifiable uncertainties in the data. Neglect of storage also distorted the relationships between the carbon exchange processes (respiration and photosynthesis) and their key controls (light and temperature, respectively). We conclude that addition of storage measurements to eddy covariance sites with all but the lowest measurement heights should be a high priority for the flux measurement community.
Impact of increasing urban density on local climate: Spatial and temporal variations in the surface energy balance in Melbourne, Australia
Publisher: American Meteorological Society
Date: 04-2007
DOI: 10.1175/JAM2462.1
Abstract: Variations in urban surface characteristics are known to alter the local climate through modification of land surface processes that influence the surface energy balance and boundary layer and lead to distinct urban climates. In Melbourne, Australia, urban densities are planned to increase under a new strategic urban plan. Using the eddy covariance technique, this study aimed to determine the impact of increasing housing density on the surface energy balance and to investigate the relationship to Melbourne’s local climate. Across four sites of increasing housing density and varying land surface characteristics (three urban and one rural), it was found that the partitioning of available energy was similar at all three urban sites. Bowen ratios were consistently greater than 1 throughout the year at the urban sites (often as high as 5) and were higher than the rural site (less than 1) because of reduced evapotranspiration. The greatest difference among sites was seen in urban heat storage, which was influenced by urban canopy complexity, albedo, and thermal admittance. Resulting daily surface temperatures were therefore different among the urban sites, yet differences in above-canopy daytime air temperatures were small because of similar energy partitioning and efficient mixing. However, greater nocturnal temperatures were observed with increasing density as a result of variations in heat storage release that are in part due to urban canyon morphology. Knowledge of the surface energy balance is imperative for urban planning schemes because there is a possibility for manipulation of land surface characteristics for improved urban climates.
Tree-grass phenology information improves light use efficiency modelling of gross primary productivity for an Australian tropical savanna
Publisher: Copernicus GmbH
Date: 30-05-2016
DOI: 10.5194/BG-2016-187
Abstract: Abstract. The coexistence of trees and grasses in savanna ecosystems results in marked phenological dynamics that vary spatially and temporally with climate. Australian savannas comprise a complex variety of life forms and phenologies, from evergreen trees to annual erennial grasses, producing a boom-bust seasonal pattern of productivity that follows the wet-dry seasonal rainfall cycle. As the climate changes into the 21st Century, modification to rainfall and temperature regimes in savannas is highly likely. There is a need to link phenology cycles of different species with productivity to understand how the tree-grass relationship may shift in response to climate change. This study investigated the relationship between productivity and phenology for trees and grasses in an Australian tropical savanna. Productivity, estimated from overstory (tree) and understory (grass) eddy covariance flux tower estimates of gross primary productivity (GPP), was compared against two years of repeat time-lapse digital photography (phenocams). We explored the phenology-productivity relationship at the ecosystem scale using moderate resolution imaging spectroradiometer (MODIS) vegetation indices and flux tower GPP. These data were obtained from the Howard Springs OzFlux/Fluxnet site (AU-How) in northern Australia. Two greenness indices were calculated from the phenocam images the green chromatic coordinate (GCC) and excess green index (ExG). These indices captured the temporal dynamics of the understory (grass) and overstory (trees) phenology, and were mostly well correlated with tower GPP for understory (r2 = 0.65 to 0.72) and overstory (r2 = 0.09 to 0.23). The MODIS enhanced vegetation index (EVI) correlated well with GPP at the ecosystem scale (r2 = 0.70). Lastly, we used GCC and EVI to parameterise a light use efficiency (LUE) model and found it to improve the estimates of GPP for the overstory, understory and ecosystem. We conclude that phenology is an important parameter to consider in estimating GPP from LUE models in savannas and that phenocams can provide important insights into the phenological variability of trees and grasses.
An optimality-based model of the dynamic feedbacks between natural vegetation and the water balance
Publisher: American Geophysical Union (AGU)
Date: 2009
DOI: 10.1029/2008WR006841
Quantifying deforestation and forest degradation with thermal response
Publisher: Elsevier BV
Date: 12-2017
DOI: 10.1016/J.SCITOTENV.2017.07.062
Abstract: Deforestation and forest degradation cause the deterioration of resources and ecosystem services. However, there are still no operational indicators to measure forest status, especially for forest degradation. In the present study, we analysed the thermal response number (TRN, calculated by daily total net radiation ided by daily temperature range) of 163 sites including mature forest, disturbed forest, planted forest, shrubland, grassland, savanna vegetation and cropland. TRN generally increased with latitude, however the regression of TRN against latitude differed among vegetation types. Mature forests are superior as thermal buffers, and had significantly higher TRN than disturbed and planted forests. There was a clear boundary between TRN of forest and non-forest vegetation (i.e. grassland and savanna) with the exception of shrubland, whose TRN overlapped with that of forest vegetation. We propose to use the TRN of local mature forest as the optimal TRN (TRN
The Australian SuperSite Network
Publisher: Elsevier BV
Date: 10-2016
DOI: 10.1016/J.SCITOTENV.2016.05.170
Abstract: Ecosystem monitoring networks aim to collect data on physical, chemical and biological systems and their interactions that shape the biosphere. Here we introduce the Australian SuperSite Network that, along with complementary facilities of Australia's Terrestrial Ecosystem Research Network (TERN), delivers field infrastructure and erse, ecosystem-related datasets for use by researchers, educators and policy makers. The SuperSite Network uses infrastructure replicated across research sites in different biomes, to allow comparisons across ecosystems and improve scalability of findings to regional, continental and global scales. This conforms with the approaches of other ecosystem monitoring networks such as Critical Zone Observatories, the U.S. National Ecological Observatory Network Analysis and Experimentation on Ecosystems, Europe Chinese Ecosystem Research Network International Long Term Ecological Research network and the United States Long Term Ecological Research Network. The Australian SuperSite Network currently involves 10 SuperSites across a erse range of biomes, including tropical rainforest, grassland and savanna wet and dry sclerophyll forest and woodland and semi-arid grassland, woodland and savanna. The focus of the SuperSite Network is on using vegetation, faunal and biophysical monitoring to develop a process-based understanding of ecosystem function and change in Australian biomes and to link this with data streams provided by the series of flux towers across the network. The Australian SuperSite Network is also intended to support a range of auxiliary researchers who contribute to the growing body of knowledge within and across the SuperSite Network, public outreach and education to promote environmental awareness and the role of ecosystem monitoring in the management of Australian environments.
OzFlux Data: Network integration from collection to curation
Publisher: Copernicus GmbH
Date: 27-05-2016
DOI: 10.5194/BG-2016-189
Abstract: Abstract. Measurement of the exchange of energy and mass between the surface and the atmospheric boundary-layer by the eddy covariance technique has undergone great change in the last two decades. Early studies of these exchanges were confined to brief field c aigns in carefully controlled conditions followed by months of data analysis. Current practice is to run tower-based eddy covariance systems continuously over several years due to the need for continuous monitoring as part of a global effort to develop local-, regional-, continental- and global-scale budgets of carbon, water and energy. Efficient methods of processing the increased quantities of data are needed to maximise the time available for analysis and interpretation. Standardised methods are needed to remove differences in data processing as possible contributors to observed spatial variability. Furthermore, public availability of these datasets assists with undertaking global research efforts. The OzFlux data path has been developed (i) to provide a standard set of quality control and post-processing tools across the network, thereby facilitating inter-site integration and spatial comparisons (ii) to increase the time available to researchers for analysis and interpretation by reducing the time spent collecting and processing data (iii) to propagate both data and metadata to the final product and (iv) to facilitate the use of the OzFlux data by adopting a standard file format and making the data available from web-based portals. The fundamentals of the OzFlux data path include the adoption of netCDF as the underlying file format to integrate data and metadata, a suite of Python scripts to provide a standard quality control, post-processing, gap filling and partitioning environment, a portal from which data can be downloaded and an OPeNDAP server offering internet access to the latest version of the OzFlux data set. Discovery of the OzFlux data set is facilitated through incorporation in FluxNet data syntheses and the publication of collection metadata via the RIF-CS format. This paper serves two purposes. The first is to describe the datasets, along with their quality control and post-processing, for the other papers of this Special Issue. The second is to provide an ex le of one solution to the data collection and curation challenges that are encountered by similar flux tower networks worldwide.
Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO)
Publisher: Copernicus GmbH
Date: 10-05-2016
DOI: 10.5194/BG-2016-188
Abstract: Abstract. Standardised, quality-controlled and robust data from flux networks underpin the understanding of ecosystem processes and tools necessary to support the management of natural resources including water, carbon and nutrients for environmental and production benefits. The Australian regional flux network (OzFlux) currently has 23 active sites and aims to provide a continental-scale national research facility to monitor and assess Australia's terrestrial biosphere and climate for improved predictions. Given the need for standardised and effective data processing of flux data we have developed a software suite called the Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO) that enables gap-filling and partitioning of the primary fluxes into ecosystem respiration and gross primary productivity and subsequently provides diagnostics and results. We outline the processing pathways and methodologies that are applied in DINGO (v12a) to OzFlux data including 1) gap-filling of meteorological and other drivers 2) gap-filling of fluxes using artificial neural networks 3) the u* threshold determination 4) partitioning into ecosystem respiration and gross primary productivity and 5) diagnostic, summary and results outputs. Opportunities remain for DINGO to incorporate robust measurements of uncertainty for application in land management and carbon accounting. In addition, footprint information is crucial in understanding and interpreting the scale and spatial influence of flux measurements. Both these features are scheduled for the next release (v13) but are detailed here. DINGO was developed for Australian data but the framework is applicable to any flux data or regional network. Quality data from robust systems like DINGO ensure the utility and uptake of the flux data and facilitates synergies between flux, remote sensing and modelling.
Net Carbon Exchange Across the Arctic Tundra-Boreal Forest Transition in Alaska 1981–2000
Publisher: Springer Science and Business Media LLC
Date: 07-2006
Quantifying the relative importance of greenhouse gas emissions from current and future savanna land use change across northern Australia
Publisher: Copernicus GmbH
Date: 23-11-2016
Abstract: Abstract. The clearing and burning of tropical savanna leads to globally significant emissions of greenhouse gases (GHGs) however there is large uncertainty relating to the magnitude of this flux. Australia's tropical savannas occupy the northern quarter of the continent, a region of increasing interest for further exploitation of land and water resources. Land use decisions across this vast biome have the potential to influence the national greenhouse gas budget. To better quantify emissions from savanna deforestation and investigate the impact of deforestation on national GHG emissions, we undertook a paired site measurement c aign where emissions were quantified from two tropical savanna woodland sites one that was deforested and prepared for agricultural land use and a second analogue site that remained uncleared for the duration of a 22-month c aign. At both sites, net ecosystem exchange of CO2 was measured using the eddy covariance method. Observations at the deforested site were continuous before, during and after the clearing event, providing high-resolution data that tracked CO2 emissions through nine phases of land use change. At the deforested site, post-clearing debris was allowed to cure for 6 months and was subsequently burnt, followed by extensive soil preparation for cropping. During the debris burning, fluxes of CO2 as measured by the eddy covariance tower were excluded. For this phase, emissions were estimated by quantifying on-site biomass prior to deforestation and applying savanna-specific emission factors to estimate a fire-derived GHG emission that included both CO2 and non-CO2 gases. The total fuel mass that was consumed during the debris burning was 40.9 Mg C ha−1 and included above- and below-ground woody biomass, course woody debris, twigs, leaf litter and C4 grass fuels. Emissions from the burning were added to the net CO2 fluxes as measured by the eddy covariance tower for other post-deforestation phases to provide a total GHG emission from this land use change. The total emission from this savanna woodland was 148.3 Mg CO2-e ha−1 with the debris burning responsible for 121.9 Mg CO2-e ha−1 or 82 % of the total emission. The remaining emission was attributed to CO2 efflux from soil disturbance during site preparation for agriculture (10 % of the total emission) and decay of debris during the curing period prior to burning (8 %). Over the same period, fluxes at the uncleared savanna woodland site were measured using a second flux tower and over the 22-month observation period, cumulative net ecosystem exchange (NEE) was a net carbon sink of −2.1 Mg C ha−1, or −7.7 Mg CO2-e ha−1. Estimated emissions for this savanna type were then extrapolated to a regional-scale to (1) provide estimates of the magnitude of GHG emissions from any future deforestation and (2) compare them with GHG emissions from prescribed savanna burning that occurs across the northern Australian savanna every year. Emissions from current rate of annual savanna deforestation across northern Australia was double that of reported (non-CO2 only) savanna burning. However, if the total GHG emission, CO2 plus non-CO2 emissions, is accounted for, burning emissions are an order of magnitude larger than that arising from savanna deforestation. We examined a scenario of expanded land use that required additional deforestation of savanna woodlands over and above current rates. This analysis suggested that significant expansion of deforestation area across the northern savanna woodlands could add an additional 3 % to Australia's national GHG account for the duration of the land use change. This bottom-up study provides data that can reduce uncertainty associated with land use change for this extensive tropical ecosystem and provide an assessment of the relative magnitude of GHG emissions from savanna burning and deforestation. Such knowledge can contribute to informing land use decision making processes associated with land and water resource development.
Spatial pattern and seasonal dynamics of the photosynthesis activity across Australian rainfed croplands
Publisher: Elsevier BV
Date: 2020
Surface energy exchanges and interactions with thunderstorms during the Maritime Continent Thunderstorm Experiment (MCTEX)
Publisher: American Geophysical Union (AGU)
Date: 05-11-2002
DOI: 10.1029/2001JD001431
Scaling of potential evapotranspiration with MODIS data reproduces flux observations and catchment water balance observations across Australia
Publisher: Elsevier BV
Date: 05-2009
Foundations for the future: A long-term plan for Australian ecosystem science
Publisher: Wiley
Date: 09-09-2014
DOI: 10.1111/AEC.12188
Carbon, water and energy fluxes in agricultural systems of Australia and New Zealand
Publisher: Elsevier BV
Date: 06-2020
Reforestation with native mixed-species plantings in a temperate continental climate effectively sequesters and stabilizes carbon within decades
Publisher: Wiley
Date: 31-10-2015
DOI: 10.1111/GCB.12746
Abstract: Reforestation has large potential for mitigating climate change through carbon sequestration. Native mixed-species plantings have a higher potential to reverse bio ersity loss than do plantations of production species, but there are few data on their capacity to store carbon. A chronosequence (5-45 years) of 36 native mixed-species plantings, paired with adjacent pastures, was measured to investigate changes to stocks among C pools following reforestation of agricultural land in the medium rainfall zone (400-800 mm yr(-1)) of temperate Australia. These mixed-species plantings accumulated 3.09 ± 0.85 t C ha(-1) yr(-1) in aboveground biomass and 0.18 ± 0.05 t C ha(-1) yr(-1) in plant litter, reaching amounts comparable to those measured in remnant woodlands by 20 years and 36 years after reforestation respectively. Soil C was slower to increase, with increases seen only after 45 years, at which time stocks had not reached the amounts found in remnant woodlands. The amount of trees (tree density and basal area) was positively associated with the accumulation of carbon in aboveground biomass and litter. In contrast, changes to soil C were most strongly related to the productivity of the location (a forest productivity index and soil N content in the adjacent pasture). At 30 years, native mixed-species plantings had increased the stability of soil C stocks, with higher amounts of recalcitrant C and higher C:N ratios than their adjacent pastures. Reforestation with native mixed-species plantings did not significantly change the availability of macronutrients (N, K, Ca, Mg, P, and S) or micronutrients (Fe, B, Mn, Zn, and Cu), content of plant toxins (Al, Si), acidity, or salinity (Na, electrical conductivity) in the soil. In this medium rainfall area, native mixed-species plantings provided comparable rates of C sequestration to local production species, with the probable additional benefit of providing better quality habitat for native biota. These results demonstrate that reforestation using native mixed-species plantings is an effective alternative for carbon sequestration to standard monocultures of production species in medium rainfall areas of temperate continental climates, where they can effectively store C, convert C into stable pools and provide greater benefits for bio ersity.
Vulnerability of native savanna trees and exoticKhaya senegalensisto seasonal drought
Publisher: Oxford University Press (OUP)
Date: 05-2015
Abstract: Seasonally dry ecosystems present a challenge to plants to maintain water relations. While native vegetation in seasonally dry ecosystems have evolved specific adaptations to the long dry season, there are risks to introduced exotic species. African mahogany, Khaya senegalensis Desr. (A. Juss.), is an exotic plantation species that has been introduced widely in Asia and northern Australia, but it is unknown if it has the physiological or phenotypic plasticity to cope with the strongly seasonal patterns of water availability in the tropical savanna climate of northern Australia. We investigated the gas exchange and water relations traits and adjustments to seasonal drought in K. senegalensis and native eucalypts (Eucalyptus tetrodonta F. Muell. and Corymbia latifolia F. Muell.) in a savanna ecosystem in northern Australia. The native eucalypts did not exhibit any signs of drought stress after 3 months of no rainfall and probably had access to deeper soil moisture late into the dry season. Leaf water potential, stomatal conductance, transpiration and photosynthesis all remained high in the dry season but osmotic adjustment was not observed. Overstorey leaf area index (LAI) was 0.6 in the native eucalypt savanna and did not change between wet and dry seasons. In contrast, the K. senegalensis plantation in the wet season was characterized by a high water potential, high stomatal conductance and transpiration and a high LAI of 2.4. In the dry season, K. senegalensis experienced mild drought stress with a predawn water potential -0.6 MPa. Overstorey LAI was halved, and stomatal conductance and transpiration drastically reduced, while minimum leaf water potentials did not change (-2 MPa) and no osmotic adjustment occurred. Khaya senegalensis exhibited an isohydric behaviour and also had a lower hydraulic vulnerability to cavitation in leaves, with a P50 of -2.3 MPa. The native eucalypts had twice the maximum leaf hydraulic conductance but a much higher P50 of -1.5 MPa. Khaya senegalensis has evolved in a wet-dry tropical climate in West Africa (600-800 mm) and appears to be well suited to the seasonal savanna climate of northern Australia. The species exhibited a large phenotypic plasticity through leaf area adjustments and conservative isohydric behaviour in the 6 months dry season while operating well above its critical hydraulic threshold.
Carbon and water exchange of the world's tallest angiosperm forest
Publisher: Elsevier BV
Date: 12-2013
Australian vegetation phenology: new insights from satellite remote sensing and digital repeat photography
Publisher: Copernicus GmbH
Date: 10-05-2016
DOI: 10.5194/BG-2016-175
Abstract: Abstract. Phenology is the study of periodic biological occurrences and can provide important insights into the influence of climatic variability and change on ecosystems. Understanding Australia’s vegetation phenology is a challenge due to its erse range of ecosystems, from savannas and tropical rainforests to temperate eucalypt woodlands, semi-arid scrublands and alpine grasslands. These ecosystems exhibit marked differences in seasonal patterns of canopy development and plant life-cycle events, much of which deviates from the predictable seasonal phenological pulse of temperate deciduous and boreal biomes. Many Australian ecosystems are subject to irregular events (i.e., drought, flooding, cyclones and fire) that can alter ecosystem composition, structure and functioning just as much as seasonal change. We show how satellite remote sensing and ground-based digital repeat photography (i.e. phenocams) can be used to improve understanding of phenology in Australian ecosystems. First, we examine temporal variation in phenology at the continental scale using the Enhanced Vegetation Index (EVI), calculated from MODerate resolution Imaging Spectroradiomter (MODIS) data. Spatial gradients are revealed, ranging from regions with pronounced seasonality in canopy development (i.e., tropical savannas) to regions where seasonal variation is minimal (i.e., tropical rainforests) or high but irregular (i.e., arid ecosystems). Next, we use time series colour information extracted from phenocam imagery to illustrate a range of phenological signals in four contrasting Australian ecosystems. These include greening and senescing events in tropical savannas and temperate eucalypt understory, as well as strong seasonal dynamics of in idual trees in a seemingly static evergreen rainforest. We also demonstrate how phenology links with ecosystem gross primary productivity (from eddy covariance) and discuss why these processes are linked in some ecosystems but not others. We conclude that phenocams have the potential to greatly improve current understanding of Australian ecosystems. To facilitate sharing of this information, we have formed the Australian Phenocam Network (phenocam.org.au/).
MODIS vegetation products as proxies of photosynthetic potential: a look across meteorological and biologic driven ecosystem productivity
Publisher: Copernicus GmbH
Date: 04-12-2015
DOI: 10.5194/BGD-12-19213-2015
Abstract: Abstract. A direct relationship between gross ecosystem productivity (GEP) measured by the eddy covariance (EC) method and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices (VIs) has been observed in many temperate and tropical ecosystems. However, in Australian evergreen forests, and particularly sclerophyll woodlands, MODIS VIs do not capture seasonality of GEP. In this study, we re-evaluate the connection between satellite and flux tower data at four contrasting Australian ecosystems, through comparisons of ecosystem photosynthetic activity (GEP) and potential (e.g. ecosystem light use efficiency and quantum yield) with MODIS vegetation satellite products, including VIs, gross primary productivity (GPPMOD), leaf area index (LAIMOD), and fraction of photosynthetic active radiation (fPARMOD). We found that satellite derived greenness products constitute a measurement of ecosystem structure (e.g. leaf area index – quantity of leaves) and function (e.g. leaf level photosynthetic assimilation capacity – quality of leaves), rather than productivity. Our results show that in primarily meteorological-driven (e.g. photosynthetic active radiation, air temperature and/or precipitation) and relatively aseasonal vegetation photosynthetic potential ecosystems (e.g. evergreen wet sclerophyll forests), there were no statistically significant relationships between GEP and satellite derived measures of greenness. In contrast, for phenology-driven ecosystems (e.g. tropical savannas), changes in the vegetation status drove GEP, and tower-based measurements of photosynthetic activity were best represented by VIs. We observed the highest correlations between MODIS products and GEP in locations where key meteorological variables and vegetation phenology were synchronous (e.g. semi-arid Acacia woodlands) and low correlation at locations where they were asynchronous (e.g. Mediterranean ecosystems). Eddy covariance data offer much more than validation and/or calibration of satellite data and models. Knowledge of the conditions in which flux tower measurements and VIs or other remote sensing products converge greatly advances our understanding of the mechanisms driving the carbon cycle (phenology and climate drivers) and provides an ecological basis for interpretation of satellite derived measures of greenness.
Carbon uptake and water use in woodlands and forests in southern Australia during an extreme heat wave event in the angry Summer of 2012/2013
Publisher: Copernicus GmbH
Date: 11-2016
Abstract: Abstract. As a result of climate change warmer temperatures are projected through the 21st century and are already increasing above modelled predictions. Apart from increases in the mean, warm/hot temperature extremes are expected to become more prevalent in the future, along with an increase in the frequency of droughts. It is crucial to better understand the response of terrestrial ecosystems to such temperature extremes for predicting land-surface feedbacks in a changing climate. While land-surface feedbacks in drought conditions and during heat waves have been reported from Europe and the US, direct observations of the impact of such extremes on the carbon and water cycles in Australia have been lacking. During the 2012/2013 summer, Australia experienced a record-breaking heat wave with an exceptional spatial extent that lasted for several weeks. In this study we synthesised eddy-covariance measurements from seven woodlands and one forest site across three biogeographic regions in southern Australia. These observations were combined with model results from BIOS2 (Haverd et al., 2013a, b) to investigate the effect of the summer heat wave on the carbon and water exchange of terrestrial ecosystems which are known for their resilience toward hot and dry conditions. We found that water-limited woodland and energy-limited forest ecosystems responded differently to the heat wave. During the most intense part of the heat wave, the woodlands experienced decreased latent heat flux (23 % of background value), increased Bowen ratio (154 %) and reduced carbon uptake (60 %). At the same time the forest ecosystem showed increased latent heat flux (151 %), reduced Bowen ratio (19 %) and increased carbon uptake (112 %). Higher temperatures caused increased ecosystem respiration at all sites (up to 139 %). During daytime all ecosystems remained carbon sinks, but carbon uptake was reduced in magnitude. The number of hours during which the ecosystem acted as a carbon sink was also reduced, which switched the woodlands into a carbon source on a daily average. Precipitation occurred after the first, most intense part of the heat wave, and the subsequent cooler temperatures in the temperate woodlands led to recovery of the carbon sink, decreased the Bowen ratio (65 %) and hence increased evaporative cooling. Gross primary productivity in the woodlands recovered quickly with precipitation and cooler temperatures but respiration remained high. While the forest proved relatively resilient to this short-term heat extreme the response of the woodlands is the first direct evidence that the carbon sinks of large areas of Australia may not be sustainable in a future climate with an increased number, intensity and duration of heat waves.
Application of problem based learning through research investigation
Publisher: Informa UK Limited
Date: 09-2007
Thermal optima of gross primary productivity are closely aligned with mean air temperatures across Australian wooded ecosystems
Publisher: Wiley
Date: 20-07-2021
DOI: 10.1111/GCB.15760
Abstract: Gross primary productivity (GPP) of wooded ecosystems (forests and savannas) is central to the global carbon cycle, comprising 67%–75% of total global terrestrial GPP. Climate change may alter this flux by increasing the frequency of temperatures beyond the thermal optimum of GPP ( T opt ). We examined the relationship between GPP and air temperature (Ta) in 17 wooded ecosystems dominated by a single plant functional type (broadleaf evergreen trees) occurring over a broad climatic gradient encompassing five ecoregions across Australia ranging from tropical in the north to Mediterranean and temperate in the south. We applied a novel boundary‐line analysis to eddy covariance flux observations to (a) derive ecosystem GPP–Ta relationships and T opt (including seasonal analyses for five tropical savannas) (b) quantitatively and qualitatively assess GPP–Ta relationships within and among ecoregions (c) examine the relationship between T opt and mean daytime air temperature (MDTa) across all ecosystems and (d) examine how down‐welling short‐wave radiation (Fsd) and vapour pressure deficit (VPD) influence the GPP–Ta relationship. GPP–Ta relationships were convex parabolas with narrow curves in tropical forests, tropical savannas (wet season), and temperate forests, and wider curves in temperate woodlands, Mediterranean woodlands, and tropical savannas (dry season). Ecosystem T opt ranged from 15℃ (temperate forest) to 32℃ (tropical savanna—wet and dry seasons). The shape of GPP–Ta curves was largely determined by daytime Ta range, MDTa, and maximum GPP with the upslope influenced by Fsd and the downslope influenced by VPD. Across all ecosystems, there was a strong positive linear relationship between T opt and MDTa (Adjusted R 2 : 0.81 Slope: 1.08) with T opt exceeding MDTa by ℃ at all but two sites. We conclude that ecosystem GPP has adjusted to local MDTa within Australian broadleaf evergreen forests and that GPP is buffered against small Ta increases in the majority of these ecosystems.
The spatial and temporal distribution of lightning strikes and their relationship with vegetation type, elevation, and fire scars in the northern Territory
Publisher: American Meteorological Society
Date: 04-2007
DOI: 10.1175/JCLI4039.1
Abstract: In this paper the authors explore the spatial and temporal patterns of lightning strikes in northern Australia for the first time. In particular, the possible relationships between lightning strikes and elevation, vegetation type, and fire scars (burned areas) are examined. Lightning data provided by the Bureau of Meteorology were analyzed for a 6-yr period (1998–2003) over the northern, southern, and coastal regions of the Northern Territory (NT) through the use of Geographical Information Systems (GIS) to determine the spatial and temporal characteristics of lightning strikes. It was determined that the highest densities of lightning strikes occurred during the monsoon transitional period (dry to wet) and during the active monsoon periods, when atmospheric moisture is highest. For the period of this study, lightning was far more prevalent over the northern region (1.21 strikes per km2 yr−1) than over the southern (0.58 strikes per km2 yr−1) and coastal regions (0.71 strikes per km2 yr−1). Differences in vegetation cover were suggested to influence the lightning distribution over the northern region of the NT, but no relationship was found in the southern region. Lightning strikes in the southern region showed a positive relationship with elevations above 800 m, but no relationship was found in the northern region, which could be due to the low-lying topography of the area. A comparison of lightning densities between burned and unburned areas showed high variability however, the authors suggest that, under ideal atmospheric conditions, large-scale fire scars (& m) could produce lightning strikes triggered by either enhanced free convection or mesoscale circulations.
Recent increases in terrestrial carbon uptake at little cost to the water cycle
Publisher: Springer Science and Business Media LLC
Date: 24-07-2017
DOI: 10.1038/S41467-017-00114-5
Abstract: Quantifying the responses of the coupled carbon and water cycles to current global warming and rising atmospheric CO 2 concentration is crucial for predicting and adapting to climate changes. Here we show that terrestrial carbon uptake (i.e. gross primary production) increased significantly from 1982 to 2011 using a combination of ground-based and remotely sensed land and atmospheric observations. Importantly, we find that the terrestrial carbon uptake increase is not accompanied by a proportional increase in water use (i.e. evapotranspiration) but is largely (about 90%) driven by increased carbon uptake per unit of water use, i.e. water use efficiency. The increased water use efficiency is positively related to rising CO 2 concentration and increased canopy leaf area index, and negatively influenced by increased vapour pressure deficits. Our findings suggest that rising atmospheric CO 2 concentration has caused a shift in terrestrial water economics of carbon uptake.
Estimating and Analyzing Savannah Phenology with a Lagged Time Series Model
Publisher: Public Library of Science (PLoS)
Date: 29-04-2016
Moving beyond methods: the need for a diverse programme in climate change research
Publisher: Wiley
Date: 27-10-2014
DOI: 10.1111/ELE.12202
Abstract: Understanding effects of climate change on ecosystems will require a erse range of approaches. We proposed using downscaled climate models to generate realistic weather scenarios as experimental treatments. Kreyling et al. propose a gradient approach to determine the shape of response functions. These approaches are different, but highly complementary.
Surface energy exchanges along a tundra-forest transition and feedbacks to climate
Publisher: Elsevier BV
Date: 08-2005
Does maximization of net carbon profit enable the prediction of vegetation behaviour in savanna sites along a precipitation gradient?
Publisher: Copernicus GmbH
Date: 11-06-2021
Abstract: Abstract. Most terrestrial biosphere models (TBMs) rely on more or less detailed information about the properties of the local vegetation. In contrast, optimality-based models require much less information about the local vegetation as they are designed to predict vegetation properties based on general principles related to natural selection and physiological limits. Although such models are not expected to reproduce current vegetation behaviour as closely as models that use local information, they promise to predict the behaviour of natural vegetation under future conditions, including the effects of physiological plasticity and shifts of species composition, which are difficult to capture by extrapolation of past observations. A previous model intercomparison using conventional terrestrial biosphere models (TBMs) revealed a range of deficiencies in reproducing water and carbon fluxes for savanna sites along a strong precipitation gradient of the North Australian Tropical Transect (Whitley et al., 2016). Here we examine the ability of an optimality-based model (the Vegetation Optimality Model, VOM) predict vegetation behaviour for the same savanna sites. The VOM optimizes key vegetation properties such as foliage cover, rooting depth and water use parameters in order to maximize the Net Carbon Profit (NCP), defined here as the difference between total carbon taken up by photosynthesis minus the carbon invested in construction and maintenance of plant organs. Despite a reduced need for input data, the VOM performed similarly or better than the conventional TBMs in terms of reproducing the seasonal litude and mean annual fluxes recorded by flux towers at the different sites. It had a relative error of 0.08 for the seasonal litude in ET, and was among the best three models tested with the smallest relative error in the seasonal litude of gross primary productivity (GPP). Nevertheless, the VOM displayed some persistent deviations from observations, especially for GPP, namely an underestimation of dry season evapo-transpiration at the wettest site, suggesting that the hydrological assumptions (free drainage) have a strong influence on the results. Furthermore, our study exposes a persistent overprediction of vegetation cover and carbon uptake during the wet seasons by the VOM. Our analysis revealed several areas for improvement in the VOM, including a better representation of the hydrological settings, as well as the costs and benefits related to plant water transport and light capture by the canopy. The results of this study imply that vegetation optimality is a promising approach to explain vegetation dynamics and the resulting fluxes. It provides a way to derive vegetation properties independently from observations, and allows for a more insightful evaluation of model shortcomings as no calibration or site-specific information is required.
Supplementary material to "Step-wise modifications of the Vegetation Optimality Model"
Publisher: Copernicus GmbH
Date: 18-06-2021
Investigating the climatic impact of urban planning strategies through the use of regional climate modelling: a case study for Melbourne, Australia
Publisher: Wiley
Date: 30-11-2008
DOI: 10.1002/JOC.1680
Photosynthetic physiology of eucalypts along a sub-continental rainfall gradient in northern Australia
Publisher: Elsevier BV
Date: 11-2011
Characteristics influencing the variability of urban CO2 fluxes in Melbourne, Australia
Publisher: Elsevier BV
Date: 2007
Erratum to
Publisher: Springer Science and Business Media LLC
Date: 25-05-2016
Impacts of an extreme cyclone event on landscape-scale savanna fire, productivity and greenhouse gas emissions
Publisher: IOP Publishing
Date: 13-11-2013
A coupled ground heat flux–surface energy balance model of evaporation using thermal remote sensing observations
Publisher: Copernicus GmbH
Date: 08-12-2022
Abstract: Abstract. One of the major undetermined problems in evaporation (ET) retrieval using thermal infrared remote sensing is the lack of a physically based ground heat flux (G) model and its integration within the surface energy balance (SEB) equation. Here, we present a novel approach based on coupling a thermal inertia (TI)-based mechanistic G model with an analytical surface energy balance model, Surface Temperature Initiated Closure (STIC, version STIC1.2). The coupled model is named STIC-TI. The model is driven by noon–night (13:30 and 01:30 local time) land surface temperature, surface albedo, and a vegetation index from MODIS Aqua in conjunction with a clear-sky net radiation sub-model and ancillary meteorological information. SEB flux estimates from STIC-TI were evaluated with respect to the in situ fluxes from eddy covariance measurements in erse ecosystems of contrasting aridity in both the Northern Hemisphere and Southern Hemisphere. Sensitivity analysis revealed substantial sensitivity of STIC-TI-derived fluxes due to the land surface temperature uncertainty. An evaluation of noontime G (Gi) estimates showed 12 %–21 % error across six flux tower sites, and a comparison between STIC-TI versus empirical G models also revealed the substantially better performance of the former. While the instantaneous noontime net radiation (RNi) and latent heat flux (LEi) were overestimated (15 % and 25 %), sensible heat flux (Hi) was underestimated (22 %). Overestimation (underestimation) of LEi (Hi) was associated with the overestimation of net available energy (RNi−Gi) and use of unclosed surface energy balance flux measurements in LEi (Hi) validation. The mean percent deviations in Gi and Hi estimates were found to be strongly correlated with satellite day–night view angle difference in parabolic and linear pattern, and a relatively weak correlation was found between day–night view angle difference versus LEi deviation. Findings from this parameter-sparse coupled G–ET model can make a valuable contribution to mapping and monitoring the spatiotemporal variability of ecosystem water stress and evaporation using noon–night thermal infrared observations from future Earth observation satellite missions such as TRISHNA, LSTM, and SBG.
Savanna fires and their impact on net ecosystem productivity in North Australia
Publisher: Wiley
Date: 25-04-2007
An optimality-based model of the coupled soil moisture and root dynamics
Publisher: Copernicus GmbH
Date: 17-06-2008
Abstract: Abstract. The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.
Quantifying the influence of local meteorology on air quality using generalized additive models
Publisher: Elsevier BV
Date: 02-2011
Improving Estimation of Seasonal Evapotranspiration in Australian Tropical Savannas using a Flexible Drought Index
Publisher: Elsevier BV
Date: 12-2020
The contribution of trees and grasses to productivity of an Australian tropical savanna
Publisher: Copernicus GmbH
Date: 26-04-2016
Abstract: Abstract. Savanna ecosystems cover 20 % of the global land surface and account for 25 % of global terrestrial carbon uptake. They support one fifth of the world's human population and are one of the most important ecosystems on our planet. Savanna productivity is a product of the interplay between trees and grass that co-dominate savanna landscapes and are maintained through interactions with climate and disturbance (fire, land use change, herbivory). In this study, we evaluate the temporally dynamic partitioning of overstory and understory carbon dioxide fluxes in Australian tropical savanna using overstory and understory eddy covariance measurements. Over a 2-year period (September 2012 to October 2014) the overall net ecosystem productivity (NEP) of the savanna was 506.2 (±22 SE) g C m−2 yr−1. The total gross primary productivity (GPP) was 2267.1 (±80 SE) g C m−2 yr−1, of which the understory contributed 32 %. The understory contribution was strongly seasonal, with most GPP occurring in the wet season (40 % of total ecosystem in the wet season and 18 % in the dry). This study is the first to elucidate the temporal dynamics of savanna understory and overstory carbon flux components explicitly using observational information. Understanding grass productivity is crucial for evaluating fuel loads, as is tree productivity for quantifying the tree carbon sink. This information will contribute to a significant refinement of the representation of savannas in models, as well as improved understanding of relative tree-grass productivity and competition for resources.
The microscale cooling effects of water sensitive urban design and irrigation in a suburban environment
Publisher: Springer Science and Business Media LLC
Date: 05-09-2018
Water Stress Explains the Aerodynamic versus Radiometric Surface Temperature Paradox in Thermal-based Evaporation Modeling
Publisher: Wiley
Date: 04-04-2022
N-fixing trees in restoration plantings: Effects on nitrogen supply and soil microbial communities
Publisher: Elsevier BV
Date: 10-2014
Land surface phenology retrievals for arid and semi-arid ecosystems
Publisher: Elsevier BV
Date: 03-2022
A test of the optimality approach to modelling canopy properties and CO2 uptake by natural vegetation
Publisher: Wiley
Date: 17-09-2007
DOI: 10.1111/J.1365-3040.2007.01728.X
Abstract: Photosynthesis provides plants with their main building material, carbohydrates, and with the energy necessary to thrive and prosper in their environment. We expect, therefore, that natural vegetation would evolve optimally to maximize its net carbon profit (NCP), the difference between carbon acquired by photosynthesis and carbon spent on maintenance of the organs involved in its uptake. We modelled N(CP) for an optimal vegetation for a site in the wet-dry tropics of north Australia based on this hypothesis and on an ecophysiological gas exchange and photosynthesis model, and compared the modelled CO2 fluxes and canopy properties with observations from the site. The comparison gives insights into theoretical and real controls on gas exchange and canopy structure, and supports the optimality approach for the modelling of gas exchange of natural vegetation. The main advantage of the optimality approach we adopt is that no assumptions about the particular vegetation of a site are required, making it a very powerful tool for predicting vegetation response to long-term climate or land use change.
Step-wise modifications of the Vegetation Optimality Model
Publisher: Copernicus GmbH
Date: 18-06-2021
DOI: 10.5194/GMD-2021-151
Abstract: Abstract. The Vegetation Optimality Model (VOM, Schymanski et al., 2009, 2015) is an optimality-based, coupled water-vegetation model that predicts vegetation properties and behaviour based on optimality theory, rather than calibrating vegetation properties or prescribing them based on observations, as most conventional models do. In order to determine wheter optimality theory can alleviate common shortcomings of conventional models, as identified in a previous model inter-comparison study along the North Australian Tropical Transect (NATT) (Whitley et al., 2016), a range of updates to previous applications of the VOM have been made for increased generality and improved comparability with conventional models. To assess in how far the updates to the model and input data would have affected the original results, we implemented them one-by-one while reproducing the analysis of Schymanski et al. (2015). The model updates included extended input data, the use of variable atmospheric CO2-levels, modified soil properties, implementation of free drainage conditions, and the addition of grass rooting depths to the optimized vegetation properties. A systematic assessment of these changes was carried out by adding each in idual modification to the original version of the VOM at the flux tower site of Howard Springs, Australia. The analysis revealed that the implemented changes affected the simulation of mean annual evapo-transpiration (ET) and gross primary productivity (GPP) by no more than 20 %, with the largest effects caused by the newly imposed free drainage conditions and modified soil texture. Free drainage conditions led to an underestimation of ET and GPP, whereas more fine-grained soil textures increased the water storage in the soil and resulted in increased GPP. Although part of the effect of free drainage was compensated for by the updated soil texture, when combining all changes, the resulting effect on the simulated fluxes was still dominated by the effect of implementing free drainage conditions. Eventually, the relative error for the mean annual ET, in comparison with flux tower observations, changed from an 8.4 % overestimation to an 10.2 % underestimation, whereas the relative errors for the mean annual GPP stayed similar with a change from 17.8 % to 14.7 %. The sensitivity to free drainage conditions suggests that a realistic representation of groundwater dynamics is very important for predicting ET and GPP at a tropical open-forest savanna site as investigated here. The modest changes in model outputs highlighted the robustness of the optimization approach that is central to the VOM architecture.
Patterns and processes of carbon, water and energy cycles across northern Australian landscapes: From point to region
Publisher: Elsevier BV
Date: 11-2011
The utility of the eddy covariance techniques as a tool in carbon accounting: tropical savanna as a case study
Publisher: CSIRO Publishing
Date: 2005
DOI: 10.1071/BT04147
Abstract: Global concern over rising atmospheric CO2 concentrations has led to a proliferation of studies of carbon cycling in terrestrial ecosystems. Associated with this has been widespread adoption of the eddy covariance method to provide direct estimates of mass and energy exchange between vegetation surfaces and the atmosphere. With the eddy covariance method, fast-response instruments (10–20Hz) are typically mounted above plant canopies and the fluxes are calculated by correlating turbulent fluctuations in vertical velocity with fluctuations in various scalars such as CO2, water vapour and temperature. These techniques allow the direct and non-destructive measurement of the net exchange of CO2 owing to uptake via photosynthesis and loss owing to respiration, evapotranspiration and sensible heat. Eddy covariance measurements have a high temporal resolution, with fluxes typically calculated at 30-min intervals and can provide daily, monthly or annual estimates of carbon uptake or loss from ecosystems. Such measurements provide a bridge between ‘bottom-up’ (e.g. leaf, soil and whole plant measures of carbon fluxes) and ‘top-down’ approaches (e.g. satellite remote sensing, air s ling networks, inverse numerical methods) to understanding carbon cycling. Eddy covariance data also provide key measurements to calibrate and validate canopy- and regional-scale carbon balance models. Limitations of the method include high establishment costs, site requirements of flat and relatively uniform vegetation and problems estimating fluxes accurately at low wind speeds. Advantages include spatial averaging over 10–100ha and near-continuous measurements. The utility of the method is illustrated in current flux studies at ideal sites in northern Australia. Flux measurements spanning 3years have been made at a mesic savanna site (Howard Springs, Northern Territory) and semi-arid savanna (Virginia Park, northern Queensland). Patterns of CO2 and water vapour exchange at diurnal, seasonal and annual scales are detailed. Carbon dynamics at these sites are significantly different and reflect differences in climate and land management (impacts of frequent fire and grazing). Such studies illustrate the utility of the eddy covariance method and its potential to provide accurate data for carbon accounting purposes. If full carbon accounting is implemented, for ideal sites, the eddy covariance method provides annual estimates of carbon sink strength accurate to within 10%. The impact of land-use change on carbon sink strength could be monitored on a long-term basis and provide a valuable validation tool if carbon trading schemes were implemented.
A comparison of gap-filling algorithms for eddy covariance fluxes and their drivers
Publisher: Copernicus GmbH
Date: 28-06-2021
Abstract: Abstract. The errors and uncertainties associated with gap-filling algorithms of water, carbon, and energy fluxes data have always been one of the main challenges of the global network of microclimatological tower sites that use the eddy covariance (EC) technique. To address these concerns and find more efficient gap-filling algorithms, we reviewed eight algorithms to estimate missing values of environmental drivers and nine algorithms for the three major fluxes typically found in EC time series. We then examined the algorithms' performance for different gap-filling scenarios utilising the data from five EC towers during 2013. This research's objectives were (a) to evaluate the impact of the gap lengths on the performance of each algorithm and (b) to compare the performance of traditional and new gap-filling techniques for the EC data, for fluxes, and separately for their corresponding meteorological drivers. The algorithms' performance was evaluated by generating nine gap windows with different lengths, ranging from a day to 365 d. In each scenario, a gap period was chosen randomly, and the data were removed from the dataset accordingly. After running each scenario, a variety of statistical metrics were used to evaluate the algorithms' performance. The algorithms showed different levels of sensitivity to the gap lengths the Prophet Forecast Model (FBP) revealed the most sensitivity, whilst the performance of artificial neural networks (ANNs), for instance, did not vary as much by changing the gap length. The algorithms' performance generally decreased with increasing the gap length, yet the differences were not significant for windows smaller than 30 d. No significant differences between the algorithms were recognised for the meteorological and environmental drivers. However, the linear algorithms showed slight superiority over those of machine learning (ML), except the random forest (RF) algorithm estimating the ground heat flux (root mean square errors – RMSEs – of 28.91 and 33.92 for RF and classic linear regression – CLR, respectively). However, for the major fluxes, ML algorithms and the MDS showed superiority over the other algorithms. Even though ANNs, random forest (RF), and eXtreme Gradient Boost (XGB) showed comparable performance in gap-filling of the major fluxes, RF provided more consistent results with slightly less bias against the other ML algorithms. The results indicated no single algorithm that outperforms in all situations, but the RF is a potential alternative for the MDS and ANNs as regards flux gap-filling.
Solar‐induced chlorophyll fluorescence exhibits a universal relationship with gross primary productivity across a wide variety of biomes
Publisher: Wiley
Date: 24-01-2019
DOI: 10.1111/GCB.14565
Abstract: In our recent study in Global Change Biology (Li et al., ), we examined the relationship between solar-induced chlorophyll fluorescence (SIF) measured from the Orbiting Carbon Observatory-2 (OCO-2) and gross primary productivity (GPP) derived from eddy covariance flux towers across the globe, and we discovered that there is a nearly universal relationship between SIF and GPP across a wide variety of biomes. This finding reveals the tremendous potential of SIF for accurately mapping terrestrial photosynthesis globally.
Temperature and human thermal comfort effects of street trees across three contrasting street canyon environments
Publisher: Springer Science and Business Media LLC
Date: 17-02-2016
Investigating the influence of synoptic-scale meteorology on air quality using self-organizing maps and generalized additive modelling
Publisher: Elsevier BV
Date: 2011
Review of Elevating the biogeosciences within environmental research networks
Publisher: Copernicus GmbH
Date: 21-03-2018
Using the paleorecord to evaluate climate and fire interactions in Australia
Publisher: Annual Reviews
Date: 05-2007
DOI: 10.1146/ANNUREV.EARTH.35.092006.145055
Abstract: Burning has been a near-continuous feature of the Australian environment but has become progressively more important since the mid-Tertiary, associated with the development of the characteristic sclerophyll vegetation. In the Quaternary, the extent of burning has varied temporally and regionally with glacial-interglacial cyclicity. Burning during glacial periods was reduced in drier areas, presumably because of a critical reduction in fuel availability, but increased in relatively wetter areas where fuel levels were high. On both glacial and Holocene timescales, peaks in charcoal often accompany transitions between fire-insensitive vegetation types, suggesting that burning is facilitated during periods of climate change and environmental instability. This suggestion has been supported by the demonstration of close relationships between fire and El Niño activity. Burning has also increased progressively over the past few hundred thousand years with major accelerations around the time of first human settlement of the continent and with the arrival of Europeans. To provide a firmer base for application of paleofire records to environmental management, there is an urgent need for a spatially more-substantial coverage of high-resolution fire records with good chronological control.
Challenges and opportunities in land surface modelling of savanna ecosystems
Publisher: Copernicus GmbH
Date: 24-10-2017
Abstract: Abstract. The savanna complex is a highly erse global biome that occurs within the seasonally dry tropical to sub-tropical equatorial latitudes and are structurally and functionally distinct from grasslands and forests. Savannas are open-canopy environments that encompass a broad demographic continuum, often characterised by a changing dominance between C3-tree and C4-grass vegetation, where frequent environmental disturbances such as fire modulates the balance between ephemeral and perennial life forms. Climate change is projected to result in significant changes to the savanna floristic structure, with increases to woody biomass expected through CO2 fertilisation in mesic savannas and increased tree mortality expected through increased rainfall interannual variability in xeric savannas. The complex interaction between vegetation and climate that occurs in savannas has traditionally challenged terrestrial biosphere models (TBMs), which aim to simulate the interaction between the atmosphere and the land surface to predict responses of vegetation to changing in environmental forcing. In this review, we examine whether TBMs are able to adequately represent savanna fluxes and what implications potential deficiencies may have for climate change projection scenarios that rely on these models. We start by highlighting the defining characteristic traits and behaviours of savannas, how these differ across continents and how this information is (or is not) represented in the structural framework of many TBMs. We highlight three dynamic processes that we believe directly affect the water use and productivity of the savanna system: phenology, root-water access and fire dynamics. Following this, we discuss how these processes are represented in many current-generation TBMs and whether they are suitable for simulating savanna fluxes.Finally, we give an overview of how eddy-covariance observations in combination with other data sources can be used in model benchmarking and intercomparison frameworks to diagnose the performance of TBMs in this environment and formulate road maps for future development. Our investigation reveals that many TBMs systematically misrepresent phenology, the effects of fire and root-water access (if they are considered at all) and that these should be critical areas for future development. Furthermore, such processes must not be static (i.e. prescribed behaviour) but be capable of responding to the changing environmental conditions in order to emulate the dynamic behaviour of savannas. Without such developments, however, TBMs will have limited predictive capability in making the critical projections needed to understand how savannas will respond to future global change.
Prospects for improving savanna biophysical models by using multiple-constraints model-data assimilation methods
Publisher: CSIRO Publishing
Date: 2005
DOI: 10.1071/BT04139
Abstract: A ‘multiple-constraints’ model-data assimilation scheme using a erse range of data types offers the prospect of improved predictions of carbon and water budgets at regional scales. Global savannas, occupying more than 12% of total land area, are an economically and ecologically important biome but are relatively poorly covered by observations. In Australia, savannas are particularly poorly s led across their extent, despite their amenity to ground-based measurement (largely intact vegetation, low relief and accessible canopies). In this paper, we describe the theoretical and practical requirements of integrating three types of data (ground-based observations, measurements of CO2/H2O fluxes and remote-sensing data) into a terrestrial carbon, water and energy budget model by using simulated observations for a hypothetical site of given climatic and vegetation conditions. The simulated data mimic specific errors, biases and uncertainties inherent in real data. Retrieval of model parameters and initial conditions by the assimilation scheme, using only one data type, led to poor representation of modelled plant-canopy production and ecosystem respiration fluxes because of errors and bias inherent in the underlying data. By combining two or more types of data, parameter retrieval was improved however, the full compliment of data types was necessary before all measurement errors and biases in data were minimised. This demonstration illustrates the potential of these techniques to improve the performance of ecosystem biophysical models by examining consistency among datasets and thereby reducing uncertainty in model parameters and predictions. Furthermore, by using existing available data, it is possible to design field c aigns with a specified network design for s ling to maximise uncertainty reduction, given available funding. Application of these techniques will not only help fill knowledge gaps in the carbon and water dynamics of savannas but will result in better information for decision support systems to solve natural-resource management problems in this biome worldwide.
Towards a remote sensing data based evapotranspiration estimation in Northern Australia using a simple random forest approach
Publisher: Elsevier BV
Date: 08-2021
A comparison of optical and microwave scintillometers with eddy covariance derived surface heat fluxes
Publisher: Elsevier BV
Date: 11-2015
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