ORCID Profile
0000-0002-2810-1722
Current Organisations
U.S. Food and Drug Administration
,
Stanford University
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Publisher: Elsevier BV
Date: 02-2014
Publisher: Copernicus GmbH
Date: 08-01-2020
Publisher: Elsevier BV
Date: 08-2011
Publisher: American Geophysical Union (AGU)
Date: 15-07-2011
DOI: 10.1029/2010WR009797
Publisher: Wiley
Date: 25-09-2021
DOI: 10.1111/GCB.15872
Abstract: Droughts in a warming climate have become more common and more extreme, making understanding forest responses to water stress increasingly pressing. Analysis of water stress in trees has long focused on water potential in xylem and leaves, which influences stomatal closure and water flow through the soil‐plant‐atmosphere continuum. At the same time, changes of vegetation water content (VWC) are linked to a range of tree responses, including fluxes of water and carbon, mortality, flammability, and more. Unlike water potential, which requires demanding in situ measurements, VWC can be retrieved from remote sensing measurements, particularly at microwave frequencies using radar and radiometry. Here, we highlight key frontiers through which VWC has the potential to significantly increase our understanding of forest responses to water stress. To validate remote sensing observations of VWC at landscape scale and to better relate them to data assimilation model parameters, we introduce an ecosystem‐scale analog of the pressure–volume curve, the non‐linear relationship between average leaf or branch water potential and water content commonly used in plant hydraulics. The sources of variability in these ecosystem‐scale pressure‐volume curves and their relationship to forest response to water stress are discussed. We further show to what extent diel, seasonal, and decadal dynamics of VWC reflect variations in different processes relating the tree response to water stress. VWC can also be used for inferring belowground conditions—which are difficult to impossible to observe directly. Lastly, we discuss how a dedicated geostationary spaceborne observational system for VWC, when combined with existing datasets, can capture diel and seasonal water dynamics to advance the science and applications of global forest vulnerability to future droughts.
Publisher: Wiley
Date: 03-12-2020
DOI: 10.1111/NPH.17040
Abstract: Plants are characterized by the iso/anisohydry continuum depending on how they regulate leaf water potential (Ψ L ). However, how iso/anisohydry changes over time in response to year‐to‐year variations in environmental dryness and how such responses vary across different regions remains poorly characterized. We investigated how dryness, represented by aridity index, affects the interannual variability of ecosystem iso/anisohydry at the regional scale, estimated using satellite microwave vegetation optical depth (VOD) observations. This ecosystem‐level analysis was further complemented with published field observations of species‐level Ψ L . We found different behaviors in the directionality and sensitivity of isohydricity (σ) with respect to the interannual variation of dryness in different ecosystems. These behaviors can largely be differentiated by the average dryness of the ecosystem itself: in mesic ecosystems, σ decreases in drier years with a higher sensitivity to dryness in xeric ecosystems, σ increases in drier years with a lower sensitivity to dryness. These results were supported by the species‐level synthesis. Our study suggests that how plants adjust their water use across years – as revealed by their interannual variability in isohydricity – depends on the dryness of plants’ living environment. This finding advances our understanding of plant responses to drought at regional scales.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-10918
Abstract: Predicting the fate of the terrestrial ecosystems and their role in the Earth system requires a quantitative and mechanistic understanding of carbon, water, and energy exchanges between the land surface and the atmosphere. While the current generation of land surface models show skill in representing many ecosystem processes, they largely disagree in the integrated response of the terrestrial biosphere to climatic change. These disagreements may be reconciled by confronting models with the erse and expanding suite of Earth system observations in order to better constrain the underlying processes. In light of this goal, we have implemented substantial developments to the CARbon DAta-MOdel FraMework (CARDAMOM)& #8212 a data assimilation system that optimally estimates parameters of a parsimonious ecosystem model& #8212 which expand its original scope as a diagnostic tool for estimating carbon states and fluxes into a system that can infer and predict the response of carbon, water and energy cycles to climate and CO2 concentrations at seasonal-to-decadal timescales. CARDAMOM 3.0 retains all functionality and model structures of previous versions, but now features a flagship model which includes coupled carbon, water, and energy cycles, along with semi-mechanistic representations of photosynthetic assimilation, allocation, phenology, autotrophic and heterotrophic respiration, snow and cold-weather processes, and soil hydrology. Additionally, the underlying framework was substantially updated in order to facilitate community use of CARDAMOM by simplifying the interface and increasing the ease with which users can integrate new observations and develop new model structures. With these new developments, CARDAMOM 3.0 provides a versatile tool for applying information from a broad array of Earth observation data to investigate carbon, water, and energy cycles and their responses to climate and atmospheric CO2 across the full range of terrestrial ecosystems, from leaf level to continental scales.
Publisher: Authorea, Inc.
Date: 27-02-2023
DOI: 10.22541/AU.167750170.06051289/V1
Abstract: Water potential is the principal driving force for the movement of water through soils and plants, and directly influences plant physiological responses. The relationships between water potential and water content in plants and soil have long been of interest, and there is increasing focus on understanding how these fundamental measures of water are linked at larger spatial and temporal scales. In this Perspective, we explore how the theory of pressure-volume relationships can be applied at ecosystem scale. We define and evaluate the concept and limitations of the ecosystem pressure-volume curve (EPV), and discuss practical ways to construct EPVs with existing data. EPVs were generated from equilibrium water potentials and water content of the above ground biomass of nine plots including tropical rainforest, savanna, temperate forest, and a long-term Amazonian rainforest drought experiment. Initial findings suggest high levels of consistency among sites where the steady-state ratio of water:biomass appears to be approximately 1:3, while ecosystem values of relative hydraulic capacitance and accessible water storage do not vary systematically with biomass. The EPV reveals useful trends across ecosystems, providing a thermodynamically consistent steady-state view of ecosystem form and function, and a biophysically robust basis for the interpretation of microwave remote sensing data.
Publisher: Elsevier BV
Date: 03-2018
Publisher: American Veterinary Medical Association (AVMA)
Date: 08-2009
Abstract: Objective —To evaluate the mechanical properties of canine carpal ligaments for use in a finite element model of the canine antebrachium. S le Population —26 forelimbs obtained from cadavers of 13 dogs euthanized for reasons unrelated to this study. Procedures —6 ligaments (medial collateral, lateral collateral, palmar ulnocarpal, palmar radiocarpal, accessorometacarpal-V, and accessorometacarpal-IV) were evaluated. Quasistatic tensile tests were performed on all specimens (n = 8 specimens/ligament) by use of a servohydraulic materials testing system in conjunction with a 6- df load cell. Each specimen was preconditioned for 10 cycles by applying 2% strain by use of a Haversine waveform. Tension was subsequently applied to each specimen at a strain rate of 0.5%/s until ligament failure. Results —Significant differences in modulus of elasticity were detected among the ligaments. Elastic modulus did not differ significantly between the 2 accessorometacapal ligaments, between the 2 collateral ligaments, or between the 2 palmar carpal ligaments. Ligaments were classified into 3 groups (accessorometacarpal ligaments, intra-articular ligaments, and palmar carpal ligaments), and significant differences were detected among the 3 ligament groups. The accessorometacarpal ligaments had a relatively high elastic modulus, compared with results for the other ligaments. The medial and lateral collateral ligaments had the lowest elastic modulus of any of the ligaments tested. Conclusions and Clinical Relevance —These results indicated a strong function-elastic modulus relationship for the 6 ligaments tested. The mechanical properties described here will be of use in creating a finite element model of the canine antebrachium.
Publisher: American Geophysical Union (AGU)
Date: 02-2012
DOI: 10.1029/2011WR011000
Publisher: American Geophysical Union (AGU)
Date: 06-2022
DOI: 10.1029/2021JG006777
Abstract: Understanding plant hydraulic regulation is critical for predicting plant and ecosystem responses to projected increases in drought stress. Plant hydraulic regulation is controlled by observable, erse plant hydraulic traits that can vary as much across in iduals of the same species as they do across different species. Direct measurements of plant hydraulic traits from a range of ecosystems remain limited in comparison to other, more readily measured traits (e.g., specific leaf area). Furthermore, plant hydraulic trait measurements, often made at leaf or branch levels, are not easily scaled to whole‐plant values that are typically used to predict plant and ecosystem fluxes. In this study, multiple whole‐plant hydraulic parameters are inferred from observations of plant water use (i.e., sap flow), soil properties, and meteorological data. We use a Markov Chain Monte Carlo model inversion approach to obtain the best estimates and uncertainty of plant hydraulic parameters that capture whole‐plant effective embolism resistance and stomatal sensitivity to decreasing plant water potential. We then use the inferred values in the model to estimate whole‐tree water use and isohydricity. This approach reliably infers whole‐plant parameter values with enough specificity to resolve inter‐ and intra‐specific differences, and thus supplements time‐ and labor‐intensive direct measurements of traits.
Publisher: Springer Science and Business Media LLC
Date: 07-02-2022
DOI: 10.1038/S41559-021-01654-2
Abstract: Extreme wildfires extensively impact human health and the environment. Increasing vapour pressure deficit (VPD) has led to a chronic increase in wildfire area in the western United States, yet some regions have been more affected than others. Here we show that for the same increase in VPD, burned area increases more in regions where vegetation moisture shows greater sensitivity to water limitation (plant-water sensitivity R 2 = 0.71). This has led to rapid increases in human exposure to wildfire risk, both because the population living in areas with high plant-water sensitivity grew 50% faster during 1990–2010 than in other wildland–urban interfaces and because VPD has risen most rapidly in these vulnerable areas. As plant-water sensitivity is strongly linked to wildfire vulnerability, accounting for ecophysiological controls should improve wildfire forecasts. If recent trends in VPD and demographic shifts continue, human wildfire risk will probably continue to increase.
Publisher: Copernicus GmbH
Date: 08-01-2020
DOI: 10.5194/BG-2019-459
Abstract: Abstract. Inter-annual variations in the tropical land carbon (C) balance are a dominant component of the global atmospheric CO2 growth rate. Currently, the lack of quantitative knowledge on processes controlling net tropical ecosystems C balance on inter-annual timescales inhibits accurate understanding and projections of land-atmosphere C exchanges. In particular, uncertainty on the relative contribution of ecosystem C fluxes attributable to concurrent meteorological forcing anomalies (concurrent effects) and those attributable to the continuing influence of past phenomena (lagged effects) stifles efforts to explicitly understand the integrated sensitivity of tropical ecosystem to climatic variability. Here we present a conceptual framework – applicable in principle to any meteorology-forced land biosphere model – to explicitly quantify net biospheric exchange (NBE) as the sum of anomaly-induced concurrent changes and climatology-induced lagged changes to terrestrial ecosystem C states (NBE = NBECON + NBELAG). We apply this framework to an observation-constrained analysis of the 2010–2015 tropical C balance: we use a data-model integration approach (CARDAMOM) to merge satellite-retrieved land-surface C observations (leaf area, biomass, solar-induced fluorescence), soil C inventory data and satellite-based atmospheric inversion estimates of CO2 and CO fluxes to produce a data-constrained analysis of the 2010–2015 tropical C cycle. We find that the inter-annual variability of lagged effects explain the majority of NBE inter-annual variability (IAV) throughout 2010–2015 across the tropics (NBELAG IAV = 112 % of NBE IAV, r = 0.87) relative to concurrent effects (NBECON IAV = 54 % of total NBE IAV, r = 0.03) and the dominance of NBELAG IAV persists across both wet and dry tropical ecosystems. The magnitude of lagged effect variations on NBE across the tropics is largely attributable to lagged effects on net primary productivity (NPP NPPLAG IAV 88 % of NBELAG IAV, r = −0.99, p-value
Publisher: Copernicus GmbH
Date: 17-12-2020
Abstract: Abstract. Inter-annual variations in the tropical land carbon (C) balance are a dominant component of the global atmospheric CO2 growth rate. Currently, the lack of quantitative knowledge on processes controlling net tropical ecosystem C balance on inter-annual timescales inhibits accurate understanding and projections of land–atmosphere C exchanges. In particular, uncertainty on the relative contribution of ecosystem C fluxes attributable to concurrent forcing anomalies (concurrent effects) and those attributable to the continuing influence of past phenomena (lagged effects) stifles efforts to explicitly understand the integrated sensitivity of a tropical ecosystem to climatic variability. Here we present a conceptual framework – applicable in principle to any land biosphere model – to explicitly quantify net biospheric exchange (NBE) as the sum of anomaly-induced concurrent changes and climatology-induced lagged changes to terrestrial ecosystem C states (NBE = NBECON+NBELAG). We apply this framework to an observation-constrained analysis of the 2001–2015 tropical C balance: we use a data–model integration approach (CARbon DAta-MOdel fraMework – CARDAMOM) to merge satellite-retrieved land-surface C observations (leaf area, biomass, solar-induced fluorescence), soil C inventory data and satellite-based atmospheric inversion estimates of CO2 and CO fluxes to produce a data-constrained analysis of the 2001–2015 tropical C cycle. We find that the inter-annual variability of both concurrent and lagged effects substantially contributes to the 2001–2015 NBE inter-annual variability throughout 2001–2015 across the tropics (NBECON IAV = 80 % of total NBE IAV, r = 0.76 NBELAG IAV = 64 % of NBE IAV, r = 0.61), and the prominence of NBELAG IAV persists across both wet and dry tropical ecosystems. The magnitude of lagged effect variations on NBE across the tropics is largely attributable to lagged effects on net primary productivity (NPP NPPLAG IAV 113 % of NBELAG IAV, r = −0.93, p value 0.05), which emerge due to the dependence of NPP on inter-annual variations in foliar C and plant-available H2O states. We conclude that concurrent and lagged effects need to be explicitly and jointly resolved to retrieve an accurate understanding of the processes regulating the present-day and future trajectory of the terrestrial land C sink.
Publisher: American Geophysical Union (AGU)
Date: 02-08-2023
DOI: 10.1029/2022GL100975
Abstract: Live fuel moisture content (LFMC) is a key determinant of landscape ignition potential, but quantitative estimates of its effects on wildfire are lacking. We present a causal inference framework to isolate the effect of LFMC from other drivers like fuel type, fuel amount, and meteorology. We show that in California when LFMC is below a critical flammability threshold, the likelihood of fires is 1.8 times as high statewide (2.25% vs. 1.27%) and 2.5 times as high in shrubs, compared to when LFMC is greater than the threshold. This risk ratio is times when LFMC is 10% less than the threshold. Between 2016 and 2021, the risk ratio was highest in 2020 (2.3 times), potentially contributing to the record‐breaking wildfire activity in 2020. Our estimates can inform several wildfire prediction and management applications, including wildfire suppression, prescribed burn planning, and public safety power shutoff implementation.
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-10625
Abstract: & & The Amazon River basin contains a substantial amount of carbon stored within terrestrial ecosystems. The unknown fate of this this carbon remains a substantial source of uncertainty in projections of the Earth system. While increasing atmospheric carbon dioxide concentrations could potentially enhance photosynthetic carbon uptake and/or reduce transpiration, increasing vapor pressure deficits have the potential to act with the opposite sign on both of these fluxes. Here, we investigate these competing factors at a process level, using a data assimilation system in which we constrain a parsimonious ecosystem model with observations from river runoff gauging stations, gravimetric water storage anomalies, and solar-induced chlorophyll fluorescence. Our model-data fusion provides us with an observationally consistent reanalysis of 21st-century ecohydrology across 14 Amazon watersheds along side the posterior distribution of key process parameters and emergent ecosystem properties such as water use efficiency (WUE). We find that the response to trends in atmospheric carbon dioxide concentrations and meteorological drivers varies across a hydroclimatic gradient within the Amazon, with implications for how carbon and water cycling could be expected to change subject to future biogeochemical and climatic trends.& &
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-10934
Abstract: & & Spatio-temporal patterns of plant water uptake, loss, and storage are a first-order control on photosynthesis, evapotranspiration dynamics, and thus, land-atmosphere interactions. These patterns depend on temporally variable hydrometeorological conditions but also on geographically varying characteristics. These include, but are not limited to, topographic and soil properties that influence rainfall infiltration and water distribution in the unsaturated zone and vegetation properties, such as rooting depth, stomatal and xylem properties, leaf area, and more. Understanding how these different factors interact to control the overall dynamics of plant water uptake is fundamental to understanding the response of vegetation to hydrologic variations, but has traditionally been hindered by data limitations. In situ measurements are too sparse to sufficiently span the range of possible variations across different geographic factors. Remote sensing estimates of plant water uptake either are not available or (in the case of ET estimates) are sufficiently indirect that they are unlikely to correctly account for all of the factors above. Here, we study the effects of different geographic factors on plant-water interactions by analyzing the dynamics of live fuel moisture content (LFMC, defined as the vegetation water content ided by dry biomass) determined from Sentinel-1 synthetic aperture radar and Landsat multispectral observations. LFMC directly reflects vegetation water content and therefore patterns of plant water uptake and evapotranspiration. We quantify the & quot lant-water sensitivity& quot by using an auto-regressive model comparing LFMC to climate and analyze the spatial patterns of plant water sensitivity at 4 km resolution across the Western United States. No in idual factor explains a majority of the spatial patterns in plant-water sensitivity. With the exception of the maximum soil conductance, no soil, topographic, or vegetation traits exerts a dominant control on plant water sensitivity. However, when aggregated, soil characteristics explain about twice as much variability in plant water sensitivity as topographic or plant characteristics do, despite little previous recognition of the influence of soil hydraulic properties on plant-water interactions.& & &
Location: United States of America
No related grants have been discovered for Alexandra Konings.