One effect that is expected to accompany global warming is the occurrence of more intense and more frequent droughts. Although it is known that protracted drought increases tree mortality, the response of forests on regional or continental scales to the kind of warmer drought that may occur in the future is poorly understood.
Breshears et al. examined the impact of recent drought on piñon pine trees in western North America, focusing on the relationships between tree die-off, temperature, and rainfall. They found that the 2000-2003 drought was not as dry as the previous one of 1953-1956, but that it occurred during a warmer period and hence might illustrate drought effects in the future. Their analysis shows that the recent drought caused a rapid regional-scale loss of overstory trees mainly due to infestation by bark beetles, outbreaks of which are commonly caused by water stress; whereas the 1950s drought affected mainly older trees, the 2000s drought killed trees of all ages. Similar widespread drought in this century could cause large changes in carbon storage and dynamics, in fluxes of near-ground solar radiation, and in patterns of runoff and erosion, as well as alter microclimate feedbacks between the land and atmosphere and reduce the production of piñon nuts, an important food source for a number of species of birds, small mammals, and local people. — HJS
Proc. Natl. Acad. Sci. U.S.A. 102, 15144 (2005).