Warming is killing trees in California parks

Mongabay: A new study ties a 22 percent increase in mortality among trees in the California Sierra Nevadas to a temperature-driven increase in drought. The research, published in the October issue of Ecology Letters, suggests that California forests "may be poised for die-back if future climates continue to feature rising temperatures without compensating increases in precipitation."

U.S. Geological Survey scientists, Phillip J. van Mantgem and Nathan L. Stephenson, measured the annual mortality of 21,338 trees in Sequoia and Yosemite national parks for more than two decades. The duration and extent of the study allowed the researchers to "correlate short-term variations in mortality with short-term variations in climate and other potential drivers of change" and assign "proximate causes of tree death... with a high degree of confidence, helping [them] identify probable mechanisms driving changes in mortality."

Van Mantgem and Nathan L. Stephenson found that mortality rates increased for all trees combined, across most elevational zones and for each of two dominant types of conifers. The deaths were linked to changes in water availability.

…The study comes as other research reveals a marked increase in the number of forest fires occurring in the Western United States….