In June 2021, a heat dome event in the Pacific Northwest caused sidewalks to buckle and killed hundreds of unprepared residents. And it wasn’t just deadly for people. A new study in the journal Global Change Biology estimates the damage to trees in Washington and Oregon adds up to scorched areas about the size of Rhode Island.
Researchers at Oregon State University’s College of Forestry knew anecdotally that the unprecedented heat turned whole hillsides from green to red or brown almost overnight. But they wanted to determine the extent of the damage.
Christopher Still, a professor of forest ecosystems and one of the authors of the study, said the best data set they had was satellite imagery and the measurements it contained. Of the forest canopy they looked at in Western Washington and Oregon, their analysis showed an estimated 1,500 square miles — or about 5% — had been damaged.
“It’s about the same size as Rhode Island, so it's quite substantial,” Still said. "And again, this is just a minimum estimate, because we don't know British Columbia."
Satellite data from Canada was not readily available, but the heat there was worse.
Professor Still said during the course of their study, three tree species jumped out as the most vulnerable to the heat: Western Hemlock, Western Red Cedar and Sitka Spruce.
“We knew that was kind of already the case, just from, like, what people had seen on the ground,” Still said.
Still said the satellite images provided a more comprehensive overview than other data sets, such as images from drone flyovers, which can be less reliable in coverage and frequency.
The study also looked at particular areas that were hardest hit.
“There's really clear pockets of lots of damage, including in Western Oregon at the coast, Southwest Washington. Olympic Peninsula jumped out as a big area of vulnerability. The National Park,” Still said. “And then in the western Cascades in Washington and Oregon, there were areas of damage too."
Glenn Kohler, a longtime forest entomologist with the Washington state Department of Natural Resources, does regular surveys of Washington’s public lands, scanning for evidence of infestations from pests such as bark beetles.
He said the heat damage looked very different: "When we looked at these trees — and we were able to map some of this from our airplane — they were only damaged on the south or west side of the tree."
“It was just mind blowing,” he said of the clear discoloration on the southern and western sides of the forest. “That's just telling you that that damage is coming directly from the sun itself. It doesn't have anything to do with lack of water... literally scorching sunburn, essentially, on the needles."
Kohler said that Douglas Fir was another vulnerable species. The heat is a newer source of potentially deadly stress — especially to seedlings or in combination with increasing drought-stress that makes some older conifers more available for infestation by bark beetles.
Still said many of these trees can recover from heat damage and rebuild the canopy, depending on their physiology and on how much moisture is available in the surrounding soil.
One of the goals of the research is to help landowners and land managers choose more resilient species when replanting.
He added that despite headwinds from the federal government canceling research funding, it’s still important to find ways to reduce emissions — and our reliance on climate-warming fossil fuels — as much as possible.
“There's a huge amount that needs to be done to figure out how we adapt and mitigate, because, certainly, climate change is running ahead full steam, and we're not going to stop it immediately,” Still said.
