Widespread tree scorch in the Pacific Northwest that became visible shortly after multiple days of record-setting, triple-digit temperatures in June 2021 was more attributable to heat than to drought conditions, Oregon State University researchers say.

In a paper published in Tree Physiology, a team led by Christopher Still of the OSU College of Forestry cites evidence that leaf discoloration and damage are consistent with direct exposure to solar radiation during the hottest afternoons of the “heat dome” that covered northwestern North America.

Heat Dome Impact

Trees on south- and west-facing slopes and on exposed edges near roadsides generally showed the greatest scorch, and opposite sides of the same trees, or other trees on the same hillsides, displayed little to none.

Still and other scientists from OSU were responding to an article published in the same journal in April 2022 that concluded the trees’ problems were the result of drought and a failure in the trees’ hydraulic system, which helps foliage stay cool through the exhalation of water vapor via a process known as transpiration.

Fast Scorching

“The scorching that did occur happened fast, within days and sometimes hours, much faster than would typically be associated with a malfunction of the trees’ water moving capabilities,” Researcher Christopher Still said.


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