The worldwide vulnerability of forests

Posted: Nov 27, 2012

Written by

JUSTIN GILLIS, New York Times

One of the great scientific tasks of the day is to understand how and why trees die. It may seem like a question that would have been answered many decades ago, but it was not — at least not at a detailed physiological level. Now, amid growing signs worldwide that forests are at risk as the climate changes, scientists are trying to catch up to events.

Lately, more and more evidence is pointing toward a mechanism known as hydraulic failure as the culprit in many large-scale forest die-backs. This occurs when drought reduces the flow of water into tree roots. The trees take measures to limit the loss of water through their leaves, but trees need water flowing through them as much as humans need blood. Eventually, if the drought is bad enough, the tiny tubes that carry water up the trunk of the plant can fill with air bubbles.

For the study, released online on Thursday by the journal Nature, Brendan Choat of the University of Western Sydney in Australia, Steven Jansen of Ulm University in Germany, and a large group of their colleagues compiled data from 226 forest species at 81 sites worldwide. They found that around 70 percent of the species operate with only a narrow margin of safety when it comes to their water supply. In other words, many of the world’s important forest species are vulnerable to hydraulic failure.

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