Detecting forest response to droughts with global observations of vegetation water content. (25th September 2021)

• Record Type: Journal Article
• Authors: Konings, Alexandra G.; Saatchi, Sassan S.; Frankenberg, Christian; Keller, Michael; Leshyk, Victor; Anderegg, William R. L.; Humphrey, Vincent; Matheny, Ashley M.; Trugman, Anna; Sack, Lawren; Agee, Elizabeth; Barnes, Mallory L.; Binks, Oliver; Cawse‐Nicholson, Kerry; Christoffersen, Bradley O.; Entekhabi, Dara; Gentine, Pierre; Holtzman, Nataniel M.; Katul, Gabriel G.; Liu, Yanlan; Longo, Marcos; Martinez‐Vilalta, Jordi; McDowell, Nate; Meir, Patrick; Mencuccini, Maurizio; Mrad, Assaad; Novick, Kimberly A.; Oliveira, Rafael S.; Siqueira, Paul; Steele‐Dunne, Susan C.; Thompson, David R.; Wang, Yujie; Wehr, Richard; Wood, Jeffrey D.; Xu, Xiangtao; Zuidema, Pieter A.;
• Is Part Of: Global change biology. Volume 27:Number 23(2021)
• Page Start: 6005
• Page End: 6024
• Publication Date: 2021-09-25
• Subjects: drought response -- drought‐induced tree mortality -- microwave remote sensing -- pressure–volume -- vegetation optical depth -- vegetation water content -- water potential; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15872
• Languages: English
• ISSNs: 1354-1013

Abstract

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. Abstract : Changes of vegetation water content (VWC) are linked to a range of tree responses to drought, including fluxes of water and carbon, mortality, flammability, and more, and can be retrieved from microwave remote sensing measurements. We highlight key frontiers through which remotely sensed VWC has the potential to significantly increase our understanding of forest responses to water stress. We argue that separate consideration of diel, seasonal, and decadal timescales can facilitate interpretation of VWC measurements for different process studies, and that VWC observations can be useful for constraining belowground water uptake. To link remotely sensed VWC estimates to plant hydraulic models, the utility and interpretation of ecosystem‐scale pressure‐volume curves are discussed.