The death rates of trees in Western U.S. forests have doubled over the past two to three decades, according to a new study spearheaded by the U.S. Geological Survey, driven in large part by higher temperatures and water scarcity linked to climate change.
The findings, being published today in the online journal Science, examined changes in 76 long-term forest plots in three broad regions across the West, and found similar shifts regardless of the areas’ elevations, fire histories, dominant species and tree sizes. It is the largest research project ever done on old-growth forests in North America.
Nathan L. Stephenson, one of the lead authors, said summers are getting longer and hotter in the West, subjecting trees to greater stress from droughts and attacks by insect infestations, factors that contribute to tree die-offs.
“It’s very likely that mortality rates will continue to rise,” said Stephenson, a scientist at the Geological Survey’s Western Ecological Research Center, adding that the death of older trees is rapidly exceeding the growth of new ones, akin to a town where the deaths of old people are outpacing the number of babies being born. “If you saw that going on in your home town, you’d be concerned.”
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