ORCID Profile
0000-0002-1605-1203
Current Organisation
Oregon State University
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Publisher: Wiley
Date: 07-08-2014
DOI: 10.1111/GCB.12671
Abstract: Understanding the environmental and biotic drivers of respiration at the ecosystem level is a prerequisite to further improve scenarios of the global carbon cycle. In this study we investigated the relevance of physiological phenology, defined as seasonal changes in plant physiological properties, for explaining the temporal dynamics of ecosystem respiration ( R ECO ) in deciduous forests. Previous studies showed that empirical R ECO models can be substantially improved by considering the biotic dependency of R ECO on the short‐term productivity (e.g., daily gross primary production, GPP ) in addition to the well‐known environmental controls of temperature and water availability. Here, we use a model‐data integration approach to investigate the added value of physiological phenology, represented by the first temporal derivative of GPP , or alternatively of the fraction of absorbed photosynthetically active radiation, for modeling R ECO at 19 deciduous broadleaved forests in the FLUXNET La Thuile database. The new data‐oriented semiempirical model leads to an 8% decrease in root mean square error ( RMSE ) and a 6% increase in the modeling efficiency ( EF ) of modeled R ECO when compared to a version of the model that does not consider the physiological phenology. The reduction of the model‐observation bias occurred mainly at the monthly time scale, and in spring and summer, while a smaller reduction was observed at the annual time scale. The proposed approach did not improve the model performance at several sites, and we identified as potential causes the plant canopy heterogeneity and the use of air temperature as a driver of ecosystem respiration instead of soil temperature. However, in the majority of sites the model‐error remained unchanged regardless of the driving temperature. Overall, our results point toward the potential for improving current approaches for modeling R ECO in deciduous forests by including the phenological cycle of the canopy.
Publisher: Elsevier BV
Date: 03-2009
Publisher: Wiley
Date: 11-12-2008
Publisher: Wiley
Date: 08-11-2013
DOI: 10.1111/PCE.12213
Abstract: Worldwide measurements of nearly 130 C3 species covering all major plant functional types are analysed in conjunction with model simulations to determine the effects of mesophyll conductance (g(m)) on photosynthetic parameters and their relationships estimated from A/Ci curves. We find that an assumption of infinite g(m) results in up to 75% underestimation for maximum carboxylation rate V(cmax), 60% for maximum electron transport rate J(max), and 40% for triose phosphate utilization rate T(u) . V(cmax) is most sensitive, J(max) is less sensitive, and T(u) has the least sensitivity to the variation of g(m). Because of this asymmetrical effect of g(m), the ratios of J(max) to V(cmax), T(u) to V(cmax) and T(u) to J(max) are all overestimated. An infinite g(m) assumption also limits the freedom of variation of estimated parameters and artificially constrains parameter relationships to stronger shapes. These findings suggest the importance of quantifying g(m) for understanding in situ photosynthetic machinery functioning. We show that a nonzero resistance to CO2 movement in chloroplasts has small effects on estimated parameters. A non-linear function with gm as input is developed to convert the parameters estimated under an assumption of infinite gm to proper values. This function will facilitate gm representation in global carbon cycle models.
Publisher: Springer Science and Business Media LLC
Date: 08-2009
Publisher: Elsevier BV
Date: 11-2009
Publisher: CSIRO Publishing
Date: 2013
DOI: 10.1071/WF12109
Abstract: Following severe wildfires, managing fire hazard by removing dead trees (post-fire logging) is an important issue globally. Data informing these management actions are relatively scarce, particularly how fuel loads differ by post-fire logging intensity within different environmental settings. In mixed-evergreen forests of Oregon, USA, we quantified fuel profiles 3–4 years after stand-replacement fire – assessing three post-fire logging intensities (0, 25–75, or % basal area cut) across two climatic settings (mesic coastal, drier interior). Stand-replacement fire consumed ~17% of aboveground biomass. Post-fire logging significantly reduced standing dead biomass, with high-intensity treatment leaving a greater proportion (28%) of felled biomass on site compared with moderate-intensity treatment (14%) because of less selective tree felling. A significant relationship between logging intensity and resulting surface fuels (per-hectare increase of 0.4–1.2Mg per square metre of basal area cut) indicated a broadly applicable predictive tool for management. Down wood cover increased by 3–5 times and became more spatially homogeneous after logging. Post-fire logging altered the fuel profile of early-seral stands (standing material removed or transferred, short-term increase in surface fuels, likely reduction in future large fuel accumulation), with moderate-intensity and unlogged treatments yielding surface fuel loads consistent with commonly prescribed levels, and high-intensity treatment resulting in greater potential need for follow-up fuel treatments.
Publisher: Copernicus GmbH
Date: 03-07-2014
Abstract: Abstract. A globally integrated carbon observation and analysis system is needed to improve the fundamental understanding of the global carbon cycle, to improve our ability to project future changes, and to verify the effectiveness of policies aiming to reduce greenhouse gas emissions and increase carbon sequestration. Building an integrated carbon observation system requires transformational advances from the existing sparse, exploratory framework towards a dense, robust, and sustained system in all components: anthropogenic emissions, the atmosphere, the ocean, and the terrestrial biosphere. The paper is addressed to scientists, policymakers, and funding agencies who need to have a global picture of the current state of the ( erse) carbon observations. We identify the current state of carbon observations, and the needs and notional requirements for a global integrated carbon observation system that can be built in the next decade. A key conclusion is the substantial expansion of the ground-based observation networks required to reach the high spatial resolution for CO2 and CH4 fluxes, and for carbon stocks for addressing policy-relevant objectives, and attributing flux changes to underlying processes in each region. In order to establish flux and stock diagnostics over areas such as the southern oceans, tropical forests, and the Arctic, in situ observations will have to be complemented with remote-sensing measurements. Remote sensing offers the advantage of dense spatial coverage and frequent revisit. A key challenge is to bring remote-sensing measurements to a level of long-term consistency and accuracy so that they can be efficiently combined in models to reduce uncertainties, in synergy with ground-based data. Bringing tight observational constraints on fossil fuel and land use change emissions will be the biggest challenge for deployment of a policy-relevant integrated carbon observation system. This will require in situ and remotely sensed data at much higher resolution and density than currently achieved for natural fluxes, although over a small land area (cities, industrial sites, power plants), as well as the inclusion of fossil fuel CO2 proxy measurements such as radiocarbon in CO2 and carbon-fuel combustion tracers. Additionally, a policy-relevant carbon monitoring system should also provide mechanisms for reconciling regional top-down (atmosphere-based) and bottom-up (surface-based) flux estimates across the range of spatial and temporal scales relevant to mitigation policies. In addition, uncertainties for each observation data-stream should be assessed. The success of the system will rely on long-term commitments to monitoring, on improved international collaboration to fill gaps in the current observations, on sustained efforts to improve access to the different data streams and make databases interoperable, and on the calibration of each component of the system to agreed-upon international scales.
Publisher: Oxford University Press (OUP)
Date: 26-10-2022
Publisher: Wiley
Date: 11-2013
DOI: 10.1890/12-0893.1
Publisher: Proceedings of the National Academy of Sciences
Date: 25-04-2016
Abstract: Carbon uptake by terrestrial ecosystems mitigates the impact of anthropogenic fossil fuel emissions on atmospheric CO 2 concentrations, but the strength of this carbon sink is highly sensitive to large-scale extreme climate events. In 2012, the United States experienced the most severe drought since the Dust Bowl period, along with the warmest spring on record. Here, we quantify the impact of this climate anomaly on the carbon cycle. Our results show that warming-induced earlier vegetation activity increased spring carbon uptake, and thus compensated for reduced carbon uptake during the summer drought in 2012. This compensation, however, came at the cost of soil moisture depletion from increased spring evapotranspiration that likely enhanced summer heating through land-atmosphere coupling.
Publisher: Oxford University Press (OUP)
Date: 27-09-2010
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
Publisher: Wiley
Date: 11-03-2004
DOI: 10.1111/J.1469-8137.2004.01053.X
Abstract: Rising atmospheric CO 2 and temperatures are probably altering ecosystem carbon cycling, causing both positive and negative feedbacks to climate. Below‐ground processes play a key role in the global carbon (C) cycle because they regulate storage of large quantities of C, and are potentially very sensitive to direct and indirect effects of elevated CO 2 and temperature. Soil organic matter pools, roots and associated rhizosphere organisms all have distinct responses to environmental change drivers, although availability of C substrates will regulate all the responses. Elevated CO 2 increases C supply below‐ground, whereas warming is likely to increase respiration and decomposition rates, leading to speculation that these effects will moderate one another. However, indirect effects on soil moisture availability and nutrient supply may alter processes in unexpected directions. Detailed, mechanistic understanding and modelling of below‐ground flux components, pool sizes and turnover rates is needed to adequately predict long‐term, net C storage in ecosystems. In this synthesis, we discuss the current status of below‐ground responses to elevated CO 2 and temperature and potential feedback effects, methodological challenges, and approaches to integrating models and measurements.
Publisher: Elsevier BV
Date: 12-2002
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-08-2006
Abstract: We reported that postfire logging 2 to 3 years after the 2002 Biscuit Fire was associated with significant mortality in natural conifer regeneration and elevated potential fire behavior in the short term as a result of increased surface fuel loads. We underscore the strength of our study design and statistical conclusions, provide additional details of the research setting and scope, and address comments pertinent to forest development and fire ecology.
Publisher: Elsevier BV
Date: 02-2022
Publisher: Canadian Science Publishing
Date: 04-2009
DOI: 10.1139/X09-016
Abstract: Large-scale wildfires (∼10 4 –10 6 ha) have the potential to eliminate seed sources over broad areas and thus may lead to qualitatively different regeneration dynamics than in small burns however, regeneration after such events has received little study in temperate forests. Following a 200 000 ha mixed-severity wildfire in Oregon, USA, we quantified (1) conifer and broadleaf regeneration in stand-replacement patches 2 and 4 years postfire and (2) the relative importance of isolation from seed sources (live trees) versus local site conditions in controlling regeneration. Patch-scale conifer regeneration density (72%–80% Douglas-fir ( Pseudotsuga menziesii (Mirb). Franco)) varied widely, from 127 to 6494 stems·ha –1 . Median densities were 1721 and 1603 stems·ha –1 2 and 4 years postfire, respectively, i.e., ∼12 times prefire overstory densities (134 stems·ha –1 ). Because of the complex burn mosaic, ∼58% of stand-replacement area was ≤200 m from a live-tree edge (seed source), and ∼81% was ≤400 m. Median conifer density exceeded 1000 stems·ha –1 out to a distance of 400 m from an edge before declining farther away. The strongest controls on regeneration were distance to live trees and soil parent material, with skeletal coarse-grained soils supporting lower densities (133 stems·ha –1 ) than fine-grained soils (729–1492 stems·ha –1 ). Other site factors (e.g., topography, broadleaf cover) had little association with conifer regeneration. The mixed-severity fire pattern strongly influenced the regeneration process by providing seed sources throughout much of the burned landscape.
Publisher: Wiley
Date: 08-06-2010
DOI: 10.1890/090179
Publisher: Wiley
Date: 23-06-2004
Publisher: Springer Science and Business Media LLC
Date: 29-08-2017
DOI: 10.1038/S41598-017-08755-8
Abstract: Concentrations of atmospheric carbon dioxide (CO 2 ) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO 2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO 2 -fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO 2 , to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.
Publisher: American Geophysical Union (AGU)
Date: 12-2011
DOI: 10.1029/2011GB004053
Publisher: Springer Science and Business Media LLC
Date: 22-09-2021
DOI: 10.1038/S41586-021-03939-9
Abstract: The leaf economics spectrum 1,2 and the global spectrum of plant forms and functions 3 revealed fundamental axes of variation in plant traits, which represent different ecological strategies that are shaped by the evolutionary development of plant species 2 . Ecosystem functions depend on environmental conditions and the traits of species that comprise the ecological communities 4 . However, the axes of variation of ecosystem functions are largely unknown, which limits our understanding of how ecosystems respond as a whole to anthropogenic drivers, climate and environmental variability 4,5 . Here we derive a set of ecosystem functions 6 from a dataset of surface gas exchange measurements across major terrestrial biomes. We find that most of the variability within ecosystem functions (71.8%) is captured by three key axes. The first axis reflects maximum ecosystem productivity and is mostly explained by vegetation structure. The second axis reflects ecosystem water-use strategies and is jointly explained by variation in vegetation height and climate. The third axis, which represents ecosystem carbon-use efficiency, features a gradient related to aridity, and is explained primarily by variation in vegetation structure. We show that two state-of-the-art land surface models reproduce the first and most important axis of ecosystem functions. However, the models tend to simulate more strongly correlated functions than those observed, which limits their ability to accurately predict the full range of responses to environmental changes in carbon, water and energy cycling in terrestrial ecosystems 7,8 .
Publisher: Wiley
Date: 04-2011
DOI: 10.1890/ES10-00184.1
Publisher: Elsevier BV
Date: 2012
No related grants have been discovered for Beverly Law.