When a Tree Dies in the Forest: Scaling Climate-Driven Tree Mortality to Ecosystem Water and Carbon Fluxes
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Drought- and heat-driven tree mortality, along with associated insect outbreaks, have been observed globally in recent decades and are expected to increase in future climates. Despite its potential to profoundly alter ecosystem carbon and water cycles, how tree mortality scales up to ecosystem functions and fluxes is uncertain. We describe a framework for this scaling where the effects of mortality are a function of the mortality attributes, such as spatial clustering and functional role of the trees killed, and ecosystem properties, such as productivity and diversity. We draw upon remote-sensing data and ecosystem flux data to illustrate this framework and place climate-driven tree mortality in the context of other major disturbances. We find that emerging evidence suggests that climate-driven tree mortality impacts may be relatively small and recovery times are remarkably fast (~4 years for net ecosystem production). We review the key processes in ecosystem models necessary to simulate the effects of mortality on ecosystem fluxes and highlight key research gaps in modeling. Overall, our results highlight the key axes of variation needed for better monitoring and modeling of the impacts of tree mortality and provide a foundation for including climate-driven tree mortality in a disturbance framework.
Keywordsdisturbance recovery resilience productivity biodiversity carbon and water fluxes
We thank the International Interdisciplinary Tree Mortality Workshop in Jena, Germany, for the discussions that led to the manuscript. W.R.L.A. was supported in part by a National Oceanic and Atmospheric Administration Climate and Global Change Postdoctoral fellowship, administered by the University Corporation of Atmospheric Research and an NSF Macrosystems Biology Grant (DEB EF-1340270). J.M.V. was supported in part by Spanish grant CGL2013-46808-R, by AGAUR (2014 SGR 453 grant), and by an ICREA Acadèmia Excellence in Research award. The postdoctoral position of M.C. was funded by the Swiss National Science Foundation (Project 140968). CyH was partially sponsored by Ministry of Science and Technology (MOST 103-2119-M-002-016-) and National Taiwan University (EcoNTU: 10R70604-2). R.S.S. was supported in part by postdoctoral fellowship of (FEDER)-Programa de Fortalecimiento en I+D+i de las Universidades 2014–2015 de la Junta de Andalucía, by CoMo-ReAdapt (CGL2013-48843-C2-1-R Spanish project), and his work has been carried out under the framework of the COST FP1106 network STReESS.
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