Environment Blamed in Western Tree Deaths

Rising temperatures and the resulting drought are causing trees in the West to die at more than twice the pace they did a few decades ago, a new study has found.

The combination of temperature and drought has also reduced the ability of the forests to absorb carbon dioxide, which traps heat and thus contributes to global warming, the authors of the study said, and has made forests sparser and more susceptible to fires and pests.

The scientists, who analyzed tree census data collected in 1955 and in later years, found that the mortality of trees increased in 87 percent of the 76 forest plots studied. In some plots, the die-off rate doubled in as little as 17 years; in others, it doubled after 29 years, the study found.

“Summers are getting longer,” said Nathan L. Stephenson, of the United States Geological Survey, a leader of the study with Phillip van Mantgem, also of the geological survey. “Trees are under more drought stress.”

The study will appear in Friday’s issue of the journal Science.

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