H.D. Adams et al. PNAS Temperature sensitivity of drought-induced tree mortality portends increased regional die-off under global-change-type drought

Proceedings of the National Academy of Sciences, published online before print April 13, 2009; doi: 10.1073/pnas.0901438106. PNAS, 106 (17), 7063-7066.

Temperature sensitivity of drought-induced tree mortality portends increased regional die-off under global-change-type drought

1. Henry D. Adams^a,^b,¹,
2. Maite Guardiola-Claramonte^a,^c,
3. Greg A. Barron-Gafford^a,^b,
4. Juan Camilo Villegas^a,^d,^e,
5. David D. Breshears^a,^b,^d,^f,
6. Chris B. Zou^g,
7. Peter A. Troch^a,^c and
8. Travis E. Huxman^a,^b,^f

1. ^aB2 EarthScience/Biosphere 2, P.O. Box 210158-B, University of Arizona, Tucson, AZ 85721, U.S.A.
2. ^bEcology and Evolutionary Biology, P.O. Box 210088, University of Arizona, Tucson, AZ 85721, U.S.A.
3. ^cHydrology and Water Resources, 1133 East James E. Rogers Way, University of Arizona, Tucson, AZ 85721, U.S.A.
4. ^dSchool of Natural Resources, P.O. Box 210043, University of Arizona, Tucson, AZ 85721, U.S.A.
5. ^eFacultad de Ingeniería, Calle 67 Numero 53 108, Universidad de Antioquia, Medellín, Colombia
6. ^fInstitute for the Study of Planet Earth, 715 N Park Ave, University of Arizona, Tucson, AZ 85721, U.S.A.
7. ^gNatural Resource Ecology and Management, 008C Ag Hall, Oklahoma State University, Stillwater, OK 74078, U.S.A.

1. Edited by Harold A. Mooney, Stanford University, Stanford, CA, and approved March 5, 2009 (received for review February 8, 2009).

Abstract

Large-scale biogeographical shifts in vegetation are predicted in response to the altered precipitation and temperature regimes associated with global climate change. Vegetation shifts have profound ecological impacts and are an important climate-ecosystem feedback through their alteration of carbon, water, and energy exchanges of the land surface. Of particular concern is the potential for warmer temperatures to compound the effects of increasingly severe droughts by triggering widespread vegetation shifts via woody plant mortality. The sensitivity of tree mortality to temperature is dependent on which of 2 non-mutually-exclusive mechanisms predominates—temperature-sensitive carbon starvation in response to a period of protracted water stress or temperature-insensitive sudden hydraulic failure under extreme water stress (cavitation). Here we show that experimentally induced warmer temperatures (≈4 °C) shortened the time to drought-induced mortality in Pinus edulis (piñon shortened pine) trees by nearly a third, with temperature-dependent differences in cumulative respiration costs implicating carbon starvation as the primary mechanism of mortality. Extrapolating this temperature effect to the historic frequency of water deficit in the southwestern United States predicts a 5-fold increase in the frequency of regional-scale tree die-off events for this species due to temperature alone. Projected increases in drought frequency due to changes in precipitation and increases in stress from biotic agents (e.g., bark beetles) would further exacerbate mortality. Our results demonstrate the mechanism by which warmer temperatures have exacerbated recent regional die-off events and background mortality rates. Because of pervasive projected increases in temperature, our results portend widespread increases in the extent and frequency of vegetation die-off.

Link to abstract: http://www.pnas.org/content/106/17/7063.abstract

Link to full, open-access article: http://www.pnas.org/content/106/17/7063.full.pdf+html