PRINCETON, N.J  -- Warming trends that favored pine beetle forest kills in millions of acres in the western United States could strike aspen forests next, says a new Princeton University study.

Aspen Trees Threatened by Hot DroughtsThe study found that large aspen die-offs are a certainty if greenhouse gas emission rates remain at the same level they have been for the past decade. Conversely, if greenhouse emissions are curbed, then aspen trees can be saved, the study found. The study models showed drought stress will exceed observed mortality threshold in the southwestern United States by the 2050s. If droughts expand, so could the deaths of aspens, the study said.

In the early 2000s droughts and uncommonly high temperatures struck western states killing large swaths of aspen trees and attracted heat-loving pine beetles, which destroyed large numbers of pine trees.

In an interview with the New York Times, William R. L. Anderegg, the Princeton University researcher who led the Princeton study, described aspen trees as “canary-in-a-coal-mine-trees.” He said aspens are “wet-loving” trees in dry landscapes, which can demonstrate how forests will behave as conditions become drier.

According to the study, which was released online at March 29, the trees die when the ground becomes overly dry and air bubbles appear in vascular tubes that carry water through the tree. Those air bubbles then block the vascular tubes ability to carry water throughout the tree.

A computer model developed by Anderegg and his colleagues can predict aspen mortality with about 75 percent accuracy.

Loss of trees, whether from disease, droughts or deforestation, has been linked to increased droughts. A December 2014 report issued by Brazil’s Center for Earth System Science, mass cutting of forests over many years has hindered the jungle’s ability to pump moisture into the air and form “sky rivers,” which are estimated to supply more than two-thirds of rain to the southeastern part of the country.  According to the study the trees pump an estimated 20 billion metric tons of water into the atmosphere every day, more than the Amazon River carries into the ocean.


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