13 results on '"Anderegg, William R. L."'
Search Results
2. Comparing Model Representations of Physiological Limits on Transpiration at a Semi‐Arid Ponderosa Pine Site.
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Hawkins, Linnia R., Bassouni, Maoya, Anderegg, William R. L., Venturas, Martin D., Good, Stephen P., Kwon, Hyojung J., Hanson, Chad V., Fiorella, Richard P., Bowen, Gabriel J., and Still, Christopher J.
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PONDEROSA pine ,DROUGHTS ,PLANT-water relationships ,LEAF temperature ,PHYSIOLOGICAL models ,VAPOR pressure ,FOREST microclimatology - Abstract
Mechanistic representations of biogeochemical processes in ecosystem models are rapidly advancing, requiring advancements in model evaluation approaches. Here we quantify multiple aspects of model functional performance to evaluate improved process representations in ecosystem models. We compare semi‐empirical stomatal models with hydraulic constraints against more mechanistic representations of stomatal and hydraulic functioning at a semi‐arid pine site using a suite of metrics and analytical tools. We find that models generally perform similarly under unstressed conditions, but performance diverges under atmospheric and soil drought. The more empirical models better capture synergistic information flows between soil water potential and vapor pressure deficit to transpiration, while the more mechanistic models are overly deterministic. Although models can be parameterized to yield similar functional performance, alternate parameterizations could not overcome structural model constraints that underestimate the unique information contained in soil water potential about transpiration. Additionally, both multilayer canopy and big‐leaf models were unable to capture the magnitude of canopy temperature divergence from air temperature, and we demonstrate that errors in leaf temperature can propagate to considerable error in simulated transpiration. This study demonstrates the value of merging underutilized observational data streams with emerging analytical tools to characterize ecosystem function and discriminate among model process representations. Plain Language Summary: Earth system models are an essential tool for understanding the consequences of changing climate conditions on forest ecosystems. Models are rapidly incorporating more realistic representations of how drought impacts ecosystem carbon and water cycling. These advancements need to be thoroughly evaluated to ensure that the models adequately capture the plant functional response to drought stress. Here we merge underutilized measurements with new analytical tools to evaluate several model representations of plant response to drought. These tools allow us to both better understand relationships among drought stress and ecosystem response, as well as quantify model accuracy. We find that models generally perform similarly under unstressed conditions, but performance diverges under drought. Key Points: We evaluate several model formulations for coupling plant hydraulic and stomatal response using functional performance metricsInformation flows from soil water potential and vapor pressure deficit to transpiration reflect structural differences among modelsConsiderable biases in modeled canopy temperature propagate to a 5% offset in cumulative growing season transpiration [ABSTRACT FROM AUTHOR]
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- 2022
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3. Exploring the impacts of unprecedented climate extremes on forest ecosystems: hypotheses to guide modeling and experimental studies.
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Holm, Jennifer A., Medvigy, David M., Smith, Benjamin, Dukes, Jeffrey S., Beier, Claus, Mishurov, Mikhail, Xiangtao Xu, Lichstein, Jeremy W., Allen, Craig D., Larsen, Klaus S., Yiqi Luo, Ficken, Cari, Pockman, William T., Anderegg, William R. L., and Rammig, Anja
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Climatic extreme events are expected to occur more frequently in the future, increasing the likelihood of unprecedented climate extremes (UCEs), or record-breaking events. UCEs, such as extreme heatwaves and droughts, substantially affect ecosystem stability and carbon cycling by increasing plant mortality and delaying ecosystem recovery. Quantitative knowledge of such effects is limited due to the paucity of experiments focusing on extreme climatic events beyond the range of historical experience. Here, we use two dynamic vegetation demographic models (VDMs), ED2 and LPJ-GUESS, to investigate the hypothesis that ecosystem responses to UCEs (e.g., unprecedented droughts) differ qualitatively from ecosystem responses to milder extremes, as a result of non-linear ecosystem responses. Additionally, we explore how unprecedented droughts in combination with increasing atmospheric CO2 and/or temperature may affect ecosystem stability and carbon cycling. We explored these questions using simulations of pre-drought and post-drought conditions at well-studied forest sites in Australia and Costa Rica. Both models produced nonlinear responses to UCEs. Due to the two models having different but plausible representations of processes and interactions, they diverge in sensitivity of biomass loss due to drought duration or intensity, and differ between each site. Biomass losses are most sensitive to drought duration in ED2, but to drought intensity in LPJ-GUESS. Elevated atmospheric CO2 concentrations (eCO2) alone did not completely buffer the ecosystems from carbon losses during UCEs in the majority of our simulations. Our findings highlight contrasting differences in process formulations and uncertainties in models, notably related to availability in plant carbohydrate storage and the diversity of plant hydraulic schemes, in projecting potential ecosystem responses to UCEs. The different hypotheses of plant responses to UCEs existing in models reflect knowledge gaps, which should be tested with targeted field experiments. This iterative modeling-experimental framework would help improve predictions of terrestrial ecosystem responses and climate feedbacks. [ABSTRACT FROM AUTHOR]
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- 2022
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4. Woody plants optimise stomatal behaviour relative to hydraulic risk
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Anderegg, William R. L., Wolf, Adam, Arango-Velez, Adriana, Choat, Brendan, Chmura, Daniel J., Jansen, Steven, Kolb, Thomas, Li, Shan, Meinzer, Frederick, Pita, Pilar, Resco de Dios, Víctor, Sperry, John S., Wolfe, Brett T., and Pacala, Stephen
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0106 biological sciences ,0301 basic medicine ,Natural resource economics ,Plant hydraulics ,Biome ,Climate change ,Time horizon ,01 natural sciences ,Carbon cycle ,03 medical and health sciences ,Water Cycle ,Ecosystem ,Water cycle ,Water-use efficiency ,Ecology, Evolution, Behavior and Systematics ,2. Zero hunger ,Drought ,Ecology ,Empirical modelling ,Water ,Extreme events ,15. Life on land ,Droughts ,030104 developmental biology ,13. Climate action ,Plant Stomata ,Environmental science ,010606 plant biology & botany - Abstract
Stomatal response to environmental conditions forms the backbone of all ecosystem and carbon cycle models, but is largely based on empirical relationships. Evolutionary theories of stomatal behaviour are critical for guarding against prediction errors of empirical models under future climates. Longstanding theory holds that stomata maximise fitness by acting to maintain constant marginal water use efficiency over a given time horizon, but a recent evolutionary theory proposes that stomata instead maximise carbon gain minus carbon costs/risk of hydraulic damage. Using data from 34 species that span global forest biomes, we find that the recent carbon‐maximisation optimisation theory is widely supported, revealing that the evolution of stomatal regulation has not been primarily driven by attainment of constant marginal water use efficiency. Optimal control of stomata to manage hydraulic risk is likely to have significant consequences for ecosystem fluxes during drought, which is critical given projected intensification of the global hydrological cycle. W.R.L.A. acknowledges funding for this research from NSF 1714972 and from the USDA National Institute of Food and Agriculture, Agricultural and Food Research Initiative Competitive Programme, Ecosystem Services and Agro-Ecosystem Management, grant no. 2017-05521. We thank T. Brodribb and one anonymous reviewer for their insightful reviews, B. Medlyn and Y.S. Lin for sharing data and R. Norby for providing Vcmax data for several species. We appreciate the assistance from Marion Feifel in collecting data of leaf photosynthetic parameters of five European tree species. S.L. acknowledges financial support from the China Scholarship Council (CSC). VRD acknowledges funding from a Ram on y Cajal fellowship (RYC-2012-10970). B.T.W. was supported by the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. DJC acknowledges funding from the National Science Centre, Poland (NN309 713340).
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- 2018
5. Opportunities, challenges and pitfalls in characterizing plant water‐use strategies.
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Kannenberg, Steven A., Guo, Jessica S., Novick, Kimberly A., Anderegg, William R. L., Feng, Xue, Kennedy, Daniel, Konings, Alexandra G., Martínez‐Vilalta, Jordi, and Matheny, Ashley M.
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DROUGHTS ,PLANT-water relationships ,PLANT capacity ,AQUATIC plants ,PLANT physiology ,PLANTS - Abstract
Classifying the diverse ways that plants respond to hydrologic stress into generalizable 'water‐use strategies' has long been an eco‐physiological research goal. While many schemes for describing water‐use strategies have proven to be quite useful, they are also associated with uncertainties regarding their theoretical basis and their connection to plant carbon and water relations. In this review, we discuss the factors that shape plant water stress responses and assess the approaches used to classify a plant's water‐use strategy, paying particular attention to the popular but controversial concept of a continuum from isohydry to anisohydry.A generalizable and predictive framework for assessing plant water‐use strategies has been historically elusive, yet recent advances in plant physiology and hydraulics provide the field with a way past these obstacles. Specifically, we promote the idea that many metrics that quantify water‐use strategies are highly dynamic and emergent from the interaction between plant traits and environmental conditions, and that this complexity has historically hindered the development of a generalizable water‐use strategy framework.This idea is explored using a plant hydraulics model to identify: (a) distinct temporal phases in plant hydraulic regulation during drought that underpin dynamic water‐use responses, and (b) how variation in both traits and environmental forcings can significantly alter common metrics used to characterize plant water‐use strategies. This modelling exercise can bridge the divide between various conceptualizations of water‐use strategies and provide targeted hypotheses to advance the understanding and quantification of plant water status regulation across spatial and temporal scales.Finally, we describe research frontiers that are necessary to improve the predictive capacity of the plant water‐use strategy concept, including further investigation into the below‐ground determinants of plant water relations, targeted data collection efforts and the potential to scale these concepts from individuals to whole regions. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]
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- 2022
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6. Competition and Drought Alter Optimal Stomatal Strategy in Tree Seedlings.
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Zenes, Nicole, Kerr, Kelly L., Trugman, Anna T., and Anderegg, William R. L.
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DROUGHT-tolerant plants ,TREE seedlings ,CARBON cycle ,WATER efficiency ,DROUGHTS ,BEHAVIOR - Abstract
A better understanding of plant stomatal strategies holds strong promise for improving predictions of vegetation responses to drought because stomata are the primary mechanism through which plants mitigate water stress. It has been assumed that plants regulate stomata to maintain a constant marginal water use efficiency and forego carbon gain when water is scarce. However, recent hypotheses pose that plants maximize carbon assimilation while also accounting for the risk of hydraulic damage via cavitation and hydraulic failure. This "gain-risk" framework incorporates competition in stomatal regulation because it takes into account that neighboring plants can "steal" unused water. This study utilizes stomatal models representing both the water use efficiency and carbon-maximization frameworks, and empirical data from three species in a potted growth chamber experiment, to investigate the effects of drought and competition on seedling stomatal strategy. We found that drought and competition responses in the empirical data were best explained by the carbon-maximization hypothesis and that both drought and competition affected stomatal strategy. Interestingly, stomatal responses differed substantially by species, with seedlings employing a riskier strategy when planted with a high water use competitor, and seedlings employing a more conservative strategy when planted with a low water use competitor. Lower water users in general had less stomatal sensitivity to decreasing Ψ
L compared to moderate to high water users. Repeated water stress also resulted in legacy effects on plant stomatal behavior, increasing stomatal sensitivity (i.e., conservative behavior) even when the seedling was returned to well-watered conditions. These results indicate that stomatal strategies are dynamic and change with climate and competition stressors. Therefore, incorporating mechanisms that allow for stomatal behavioral changes in response to water limitation may be an important step to improving carbon cycle projections in coupled climate-Earth system models. [ABSTRACT FROM AUTHOR]- Published
- 2020
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7. Leveraging plant hydraulics to yield predictive and dynamic plant leaf allocation in vegetation models with climate change.
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Trugman, Anna T., Anderegg, Leander D. L., Sperry, John S., Wang, Yujie, Venturas, Martin, and Anderegg, William R. L.
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CLIMATE change models ,FOLIAGE plants ,PLANT yields ,ECOSYSTEM dynamics ,PLANTS - Abstract
Plant functional traits provide a link in process‐based vegetation models between plant‐level physiology and ecosystem‐level responses. Recent advances in physiological understanding and computational efficiency have allowed for the incorporation of plant hydraulic processes in large‐scale vegetation models. However, a more mechanistic representation of water limitation that determines ecosystem responses to plant water stress necessitates a re‐evaluation of trait‐based constraints for plant carbon allocation, particularly allocation to leaf area. In this review, we examine model representations of plant allocation to leaves, which is often empirically set by plant functional type‐specific allometric relationships. We analyze the evolution of the representation of leaf allocation in models of different scales and complexities. We show the impacts of leaf allocation strategy on plant carbon uptake in the context of recent advancements in modeling hydraulic processes. Finally, we posit that deriving allometry from first principles using mechanistic hydraulic processes is possible and should become standard practice, rather than using prescribed allometries. The representation of allocation as an emergent property of scarce resource constraints is likely to be critical to representing how global change processes impact future ecosystem dynamics and carbon fluxes and may reduce the number of poorly constrained parameters in vegetation models. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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8. Plant functional traits and climate influence drought intensification and land-atmosphere feedbacks.
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Anderegg, William R. L., Trugman, Anna T., Bowling, David R., Salvucci, Guido, and Tuttle, Samuel E.
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LAND-atmosphere interactions , *PLANT transpiration , *CLIMATE feedbacks , *DROUGHTS , *CLIMATE extremes , *CLIMATOLOGY , *SOIL moisture - Abstract
The fluxes of energy, water, and carbon from terrestrial ecosystems influence the atmosphere. Land-atmosphere feedbacks can intensify extreme climate events like severe droughts and heatwaves because low soil moisture decreases both evaporation and plant transpiration and increases local temperature. Here, we combine data from a network of temperate and boreal eddy covariance towers, satellite data, plant trait datasets, and a mechanistic vegetation model to diagnose the controls of soil moisture feedbacks to drought. We find that climate and plant functional traits, particularly those related to maximum leaf gas exchange rate and water transport through the plant hydraulic continuum, jointly affect drought intensification. Our results reveal that plant physiological traits directly affect drought intensification and indicate that inclusion of plant hydraulic transport mechanisms in models may be critical for accurately simulating land-atmosphere feedbacks and climate extremes under climate change. [ABSTRACT FROM AUTHOR]
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- 2019
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9. Testing early warning metrics for drought‐induced tree physiological stress and mortality.
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Anderegg, William R. L., Anderegg, Leander D. L., and Huang, Cho‐ying
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PHYSIOLOGICAL stress , *NATURAL disaster warning systems , *LANDSAT satellites , *MORTALITY , *FOREST management , *SPATIAL ability - Abstract
Climate change‐driven drought stress has triggered numerous large‐scale tree mortality events in recent decades. Advances in mechanistic understanding and prediction are greatly limited by an inability to detect in situ where trees are likely to die in order to take timely measurements and actions. Thus, algorithms of early warning and detection of drought‐induced tree stress and mortality could have major scientific and societal benefits. Here, we leverage two consecutive droughts in the southwestern United States to develop and test a set of early warning metrics. Using Landsat satellite data, we constructed early warning metrics from the first drought event. We then tested these metrics' ability to predict spatial patterns in tree physiological stress and mortality from the second drought. To test the broader applicability of these metrics, we also examined a separate drought in the Amazon rainforest. The early warning metrics successfully explained subsequent tree mortality in the second drought in the southwestern US, as well as mortality in the independent drought in tropical forests. The metrics also strongly correlated with spatial patterns in tree hydraulic stress underlying mortality, which provides a strong link between tree physiological stress and remote sensing during the severe drought and indicates that the loss of hydraulic function during drought likely mediated subsequent mortality. Thus, early warning metrics provide a critical foundation for elucidating the physiological mechanisms underpinning tree mortality in mature forests and guiding management responses to these climate‐induced disturbances. [ABSTRACT FROM AUTHOR]
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- 2019
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10. Distributed Plant Hydraulic and Hydrological Modeling to Understand the Susceptibility of Riparian Woodland Trees to Drought‐Induced Mortality.
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Tai, Xiaonan, Mackay, D. Scott, Sperry, John S., Brooks, Paul, Anderegg, William R. L., Flanagan, Lawrence B., Rood, Stewart B., and Hopkinson, Christopher
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GROUNDWATER research ,HYDROLOGY ,MORTALITY - Abstract
Abstract: The mechanistic understanding of drought‐induced forest mortality hinges on improved models that incorporate the interactions between plant physiological responses and the spatiotemporal dynamics of water availability. We present a new framework integrating a three‐dimensional groundwater model, Parallel Flow, with a physiologically sophisticated plant model, Terrestrial Regional Ecosystem Exchange Simulator. The integrated model, Parallel Flow‐Terrestrial Regional Ecosystem Exchange Simulator, was demonstrated to quantify the susceptibility of riparian cottonwoods (Populus angustifolia, Populus deltoides, and native hybrids) in southwestern Canada to sustained atmospheric drought and variability in stream flow. The model reasonably captured the dynamics of soil moisture and evapotranspiration in both wet and dry years, including the resilience of cottonwoods despite their high vulnerability to xylem cavitation. Unrealistic predictions of mortality could be generated when ignoring lateral groundwater flow. Our results also illustrated a mechanistic linkage between streamflow and cottonwood health. In the absence of precipitation, normal streamflow could sustain 94% of cottonwoods, and higher streamflows would be required to sustain all of the floodplain cottonwoods. Further, the risk of mortality was mediated by plant hydraulic properties. These results underpin the importance of integrating groundwater processes and plant hydraulics in order to analyze the forest response to sustained severe drought, which could increase in the future due to climate change combined with increasing river water withdrawals. [ABSTRACT FROM AUTHOR]
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- 2018
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11. Plant hydraulics improves and topography mediates prediction of aspen mortality in southwestern USA.
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Tai, Xiaonan, Mackay, D. Scott, Anderegg, William R. L., Sperry, John S., and Brooks, Paul D.
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HYDRAULICS ,CLIMATE change ,DROUGHTS ,SOIL moisture ,PLANT physiology - Abstract
Elevated forest mortality has been attributed to climate change-induced droughts, but prediction of spatial mortality patterns remains challenging. We evaluated whether introducing plant hydraulics and topographic convergence-induced soil moisture variation to land surface models ( LSM) can help explain spatial patterns of mortality., A scheme predicting plant hydraulic safety loss from soil moisture was developed using field measurements and a plant physiology-hydraulics model, TREES. The scheme was upscaled to Populus tremuloides forests across Colorado, USA, using LSM-modeled and topography-mediated soil moisture, respectively. The spatial patterns of hydraulic safety loss were compared against aerial surveyed mortality., Incorporating hydraulic safety loss raised the explanatory power of mortality by 40% compared to LSM-modeled soil moisture. Topographic convergence was mostly influential in suppressing mortality in low and concave areas, explaining an additional 10% of the variations in mortality for those regions., Plant hydraulics integrated water stress along the soil-plant continuum and was more closely tied to plant physiological response to drought. In addition to the well-recognized topo-climate influence due to elevation and aspect, we found evidence that topographic convergence mediates tree mortality in certain parts of the landscape that are low and convergent, likely through influences on plant-available water. [ABSTRACT FROM AUTHOR]
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- 2017
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12. Forest mortality due to drought: latest insights, evidence and unresolved questions on physiological pathways and consequences of tree death.
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Zeppel, Melanie J. B., Anderegg, William R. L., and Adams, Henry D.
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ECOLOGY conferences , *FOREST mortality , *PLANT mortality , *DROUGHTS - Abstract
The article discusses different presentations made at the 97th Annual Meeting of the Ecological Society of America, held in Portland, Oregon, in August 2012. The event focused on the causes of forest mortality due to drought. Nate McDowell from Los Alamos National Laboratory, New Mexico, talked about the processes involved in drought-induced mortality. Amy Whipple from Northern Arizona University described links between drought related mortality and genetics.
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- 2013
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13. Xylem embolism refilling and resilience against drought-induced mortality in woody plants: processes and trade-offs
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Georg von Arx, Melanie J. B. Zeppel, Nadine K. Ruehr, Tamir Klein, Martin G. De Kauwe, William R. L. Anderegg, Jasper Bloemen, Andrea Nardini, Thomas L. Powell, Patrick J. Hudson, Klein, Tamir, Zeppel, Melanie J. B., Anderegg, William R. L., Bloemen, Jasper, De Kauwe, Martin G., Hudson, Patrick, Ruehr, Nadine K., Powell, Thomas L., von Arx, Georg, and Nardini, Andrea
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0106 biological sciences ,0301 basic medicine ,Drought stress ,Evolution ,media_common.quotation_subject ,Hydraulic conductivity ,Plant hydraulics ,Plant Biology & Botany ,Plant hydraulic ,Plant water relations ,Biology ,01 natural sciences ,03 medical and health sciences ,Behavior and Systematics ,Recovery ,medicine ,Ecology, Evolution, Behavior and Systematics ,media_common ,Ecology ,Axial parenchyma ,Trade offs ,fungi ,Xylem ,Repair ,food and beverages ,Plant water relation ,Biological Sciences ,medicine.disease ,030104 developmental biology ,Embolism ,Psychological resilience ,Tree species ,Environmental Sciences ,010606 plant biology & botany ,Woody plant - Abstract
© 2018, The Ecological Society of Japan. Understanding which species are able to recover from drought, under what conditions, and the mechanistic processes involved, will facilitate predictions of plant mortality in response to global change. In response to drought, some species die because of embolism-induced hydraulic failure, whilst others are able to avoid mortality and recover, following rehydration. Several tree species have evolved strategies to avoid embolism, whereas others tolerate high embolism rates but can recover their hydraulic functioning upon drought relief. Here, we focus on structures and processes that might allow some plants to recover from drought stress via embolism reversal. We provide insights into how embolism repair may have evolved, anatomical and physiological features that facilitate this process, and describe possible trade-offs and related costs. Recent controversies on methods used for estimating embolism formation/repair are also discussed, providing some methodological suggestions. Although controversial, embolism repair processes are apparently based on the activity of phloem and ray/axial parenchyma. The mechanism is energetically demanding, and the costs to plants include metabolism and transport of soluble sugars, water and inorganic ions. We propose that embolism repair should be considered as a possible component of a ‘hydraulic efficiency-safety’ spectrum. We also advance a framework for vegetation models, describing how vulnerability curves may change in hydrodynamic model formulations for plants that recover from embolism.
- Published
- 2018
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