Alan L. Flint Cho-ying Huang Lorraine E. Flint Joseph A. Berry Frank W. Davis John S. Sperry Christopher B. Field William R.L. Anderegg 2015 <p><span>The projected responses of forest ecosystems to warming and drying associated with twenty-first-century climate change vary widely from resiliency to widespread tree mortality</span>^{<a id="ref-link-2" title="Cox, P. M. et al. Amazonian forest dieback under climate-carbon cycle projections for the 21st century. Theor. Appl. Clim. 78, 137-156 (2004)." href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref1" data-mce-href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref1">1</a>, <a id="ref-link-3" title="Scholze, M., Knorr, W., Arnell, N. W. &amp; Prentice, I. C. A climate-change risk analysis for world ecosystems. Proc. Natl Acad. Sci. USA 103, 13116-13120 (2006)." href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref2" data-mce-href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref2">2</a>, <a id="ref-link-4" title="Huntingford, C. et al. Simulated resilience of tropical rainforests to CO2-induced climate change. Nature Geosci. 6, 268-273 (2013)." href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref3" data-mce-href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref3">3</a>}<span>. Current vegetation models lack the ability to account for mortality of overstorey trees during extreme drought owing to uncertainties in mechanisms and thresholds causing mortality</span>^{<a id="ref-link-5" title="McDowell, N. G. et al. The interdependence of mechanisms underlying climate-driven vegetation mortality. Trends Ecol. Evol. 26, 523-532 (2011)." href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref4" data-mce-href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref4">4</a>, <a id="ref-link-6" title="Powell, T. L. et al. Confronting model predictions of carbon fluxes with measurements of Amazon forests subjected to experimental drought. New Phytol. 200, 350-365 (2013)." href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref5" data-mce-href="http://www.nature.com/ngeo/journal/v8/n5/full/ngeo2400.html#ref5">5</a>}<span>. Here we assess the causes of tree mortality, using field measurements of branch hydraulic conductivity during ongoing mortality in </span><i>Populus tremuloides</i><span> in the southwestern United States and a detailed plant hydraulics model. We identify a lethal plant water stress threshold that corresponds with a loss of vascular transport capacity from air entry into the xylem. We then use this hydraulic-based threshold to simulate forest dieback during historical drought, and compare predictions against three independent mortality data sets. The hydraulic threshold predicted with 75% accuracy regional patterns of tree mortality as found in field plots and mortality maps derived from Landsat imagery. In a high-emissions scenario, climate models project that drought stress will exceed the observed mortality threshold in the southwestern United States by the 2050s. Our approach provides a powerful and tractable way of incorporating tree mortality into vegetation models to resolve uncertainty over the fate of forest ecosystems in a changing&nbsp;climate.</span></p> application/pdf 10.1038/NGEO2400 en Nature Publishing Group Tree mortality predicted from drought-induced vascular damage article