The Science

This study reviewed the literature to identify key mechanisms underlying warming-induced woody-plant mortality, including trees and shrubs, and presented a testable framework that yields insight into the drivers of plant death as well as how to better model these processes. Ultimately, mortality under drought, rising temperature, and rising carbon dioxide result from depletion of water and carbon stores, leading to irreversible dehydration and the inability to maintain metabolism. Warming exacerbates these storage declines, while elevated carbon dioxide has mixed impacts. The net result of the increasing rate and severity of warming and drought overwhelms the benefits of elevated carbon.

The Impact

Plant mortality is rising globally, leading to negative impacts on ecosystem services of societal value, including economic, aesthetic, and ecological consequences. Plant mortality is rising in concert with increasing droughts, warming, and carbon dioxide, but the mechanisms driving the increased mortality are poorly known. This knowledge gap leads to large challenges for predicting the future of terrestrial ecosystems, including their role in water, carbon, and nutrient cycling. This study integrated the literature on plant mortality and subsequently generated a synthetic and testable hypothesis framework describing the mechanisms underlying plant death in a warming and drying world.

Summary

Increasing rates of woody-plant mortality, including trees and shrubs, presents a large scientific challenge due to an insufficient understanding of the cause of rising plant loss. Plant mortality reduces carbon uptake and increases carbon loss, promoting a decline in terrestrial carbon storage. Despite these consequences, predicting plant mortality is limited by a lack of knowledge of the underlying mechanisms, their response to climate, and their integration into models. Here, scientists reviewed the literature to generate a synthetic hypothesis framework that pinpoints key mechanisms driving mortality under a changing environment. The result of this study is a roadmap for future research, including the provision of a set of testable hypotheses that will rapidly increase understanding and identification of key mechanisms that should be included in process models to enable more accurate representation of the impacts of climate change on plant survival. Carbon and water stores are depleted under changing climate, with some amelioration due to rising carbon dioxide. The decline in these stores not only leads to failure to maintain hydration and metabolism but can also promote death outright or through failure to defend against attacking biotic agents. Acclimation can promote survival to an extent. Determining the net impacts of rising carbon dioxide versus drought and warming remain a major science challenge.

Principal Investigator

Nate McDowell
Pacific Northwest National Laboratory
nate.mcdowell@pnnl.gov

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
brian.benscoter@science.doe.gov

Funding

N. G. M. and C. X. were supported by the Next-Generation Ecosystem Experiments–Tropics (NGEE–Tropics) project in the U.S. Department of Energy’s (DOE) Office of Science. G. S. was supported by the NSFBII-Implementation (2021898). D. T. acknowledges support from the Australian Research Council (DP0879531, DP110105102, LP0989881, LP140100232). M. D. K acknowledges support from the Australian Research Council (ARC) Centre of Excellence for Climate Extremes (CE170100023), the ARC Discovery Grant (DP190101823) and the NSW Research Attraction and Acceleration Program. C. G. was supported by the Swiss National Science Foundation (PZ00P3_174068). M. M. and J.M.V were supported by the Spanish Ministry of Science and Innovation (MICINN, CGL2017‐89149‐C2‐1‐R). A.T.T. acknowledges funding from the NSF Grant 2003205, the USDA National Institute of Food and Agriculture, Agricultural and Food Research Initiative Competitive Programme Grant No. 2018-67012-31496 and the University of California Laboratory Fees Research Program Award No. LFR-20-652467. W.M.H. was supported by the NSF GRFP (1-746055). A.M.T. and H.D.A. were supported by the NSF Division of Integrative Organismal Systems, Integrative Ecological Physiology Program (IOS-1755345, IOS-1755346). H.D.A. also received support from the USDA National Institute of Food and Agriculture (NIFA), McIntire Stennis Project WNP00009 and Agriculture and Food Research Initiative award 2021-67013-33716. D.D.B. was supported by NSF (DEB-1550756, DEB-1824796, DEB-1925837), USGS SW Climate Adaptation Science Center (G18AC00320), USDA NIFA McIntire Stennis ARZT 1390130-M12-222, and a Murdoch University Distinguished Visiting Scholar award. D.S.M. was supported by NSF (IOS-1444571, IOS- 1547796). R.S.O. acknowledges funding from NERC-FAPESP 19/07773-1. W.R.L.A. was supported by the David and Lucille Packard Foundation, NSF grants 1714972, 1802880 and 2003017, and USDA NIFA AFRI grant no. 2018‐67019‐27850. R.S.O. acknowledges funding from NERC-FAPESP 19/07773-1. B.E.M. is supported by an Australian Research Council Laureate Fellowship (FL190100003. A.S. was supported by a Bullard Fellowship (Harvard University) and the University of Montana.

References