In the Sierra Nevada mountains of California, climate change is subtly eroding the health of pine and fir trees. The effect could be a portent of severe tree die-offs to come.
Ecologists have been tracking the fate of more than 21,000 individual trees since 1983 as part of a project to study forest ecology at different elevations in the Californian mountains. When Phillip van Mantgem and Nathan Stephenson of the US Geological Survey in Three Rivers, California, looked at the first 22 years of this record, they noticed that mortality rates of both pine and fir trees had increased at an average of 3% a year, nearly doubling overall (Ecology Letters, DOI: 10.1111/j.1461-0248.2007.01080.x). The increased death rates were seen at all but the highest elevations. Meanwhile, the rate at which new trees established did not change.
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