'Tree physiologists have worked a lot to show that hydraulic damage in response to drought drives a lot of tree mortality, and the paper we comment on more or less fits in that vein, implying that what we saw in June 2021 was just another example of drought damage and that the heat dome was a sort of extreme drought event.' 'While we think the drought/hydraulic hypothesis is partly true, we argue that multiple lines of evidence suggest the main issue was in fact direct heat damage,' said Still, a tree physiologist who studies forests in the context of climate change impacts and feedbacks. The collaboration that produced the response following a literature review includes researchers from Oregon State's colleges of Engineering, Agricultural Sciences, and Earth, Ocean, and Atmospheric Sciences, as well as two other OSU-affiliated organizations, the Oregon Climate Change Research Institute and the PRISM Climate Group.

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. 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.

Trees of the pacific northwest