Sierra trees stressed
Conifer trees in the Sierra Nevada are dying at twice the rate they were 22 years ago, according to a study by the U.S. Geological Survey. The study began in 1983 and covered 21,338 trees along a 400-mile-long range of various forests—ponderosa pine-mixed conifer, white fir-mixed conifer, red fir, Jeffrey pine and subalpine. During that time, the average mortality rate increased every year by roughly 3 percent and nearly doubled by the end of the study. Hotter temperatures, decreased precipitation and insect infestation have stressed the trees, lowering their survival odds during dry spells they once were able to weather. “What surprised us are how sensitive these trees are to short-term changes in climate,” Phillip van Mantgem, a USGS ecologist and author of the report, told the Associated Press. During the course of the study, the Sierra Nevada warmed by 1.8 degrees Fahrenheit, while snow and rain levels stayed the same.