Temperature as a Potent Driver of Regional Forest Drought Stress and Tree Mortality

By A. Park Williams, Craig D. Allen, Alison K. Macalady, Daniel Griffin, Connie A. Woodhouse, David M. Meko, Thomas W. Swetnam, Sara A. Rauscher, Richard Seager, Henri D. Grissino-Mayer, Jeffrey S. Dean, Edward R. Cook, Chandana Gangodagamage, Michael Cai & Nate G. McDowell

Nature Climate Change (September 30, 2012) – Combine the tree-ring growth record with historical information, climate records, and computer-model projections of future climate trends, and you get a grim picture for the future of trees in the southwestern United States. That’s the word from a team of scientists from Los Alamos National Laboratory, the U.S. Geological Survey, the University of Arizona, and other partner organizations. If the Southwest is warmer and drier in the near future, widespread tree death is likely and would cause substantial changes in the distribution of forests and of species, the researchers report in the journal Nature Climate Change.

As the climate changes, drought may reduce tree productivity and survival across many forest ecosystems; however, the relative influence of specific climate parameters on forest decline is poorly understood. Researchers derive a forest drought-stress index (FDSI) for the southwestern United States using a comprehensive tree-ring data set representing AD 1000–2007.

The FDSI is approximately equally influenced by the warm-season vapour-pressure deficit (largely controlled by temperature) and cold-season precipitation, together explaining 82% of the FDSI variability. Correspondence between the FDSI and measures of forest productivity, mortality, bark-beetle outbreak and wildfire validate the FDSI as a holistic forest-vigour indicator.

If the vapour-pressure deficit continues increasing as projected by climate models, the mean forest drought-stress by the 2050s will exceed that of the most severe droughts in the past 1,000 years. Collectively, the results foreshadow twenty-first-century changes in forest structures and compositions, with transition of forests in the southwestern United States, and perhaps water-limited forests globally, towards distributions unfamiliar to modern civilization.

Related Resources:
Temperature as a Potent Driver of Regional Forest Drought Stress and Tree Mortality
Climate Change Could Cripple Southwestern U.S. Forests: Trees Face Rising Drought Stress and Mortality as Climate Warms