Drier summers are killing Oregon's native trees; residents, scientists worried

Oregon’s iconic Douglas firs are declining as the state’s summers have grown hotter and drier.

Drought also is killing grand fir, and may be contributing to declines in Western red cedar and bigleaf maple.

“A lot of people really notice it, especially driving down I-5,” said Christine Buhl, an entomologist for the Oregon Department of Forestry. “They see a lot of dead trees in the hills.”

Oregon has experienced drought each summer since 2012, peaking in 2015. While rainfall and snowpack have been close to average the past two years, temperatures in many areas still were above normal. Climate change is expected to increase drought in Oregon.

Oregon Department of Forestry scientists conduct statewide aerial and ground tree surveys across 30 million acres each year, recording the number of dead and dying trees from all causes, including drought, storms, disease and insect damage.

They look for indicators of of drought stress, such as sparse or asymmetrical crowns, an abnormally high number of cones, and brown or dead branches.

In 2018, about 680,000 acres contained damaged or dead trees attributed to all causes. That’s fewer than at the peak of the drought but still higher than historic levels.

House Rock:Campground features idyllic swimming, hiking on South Santiam River

Doug fir, Oregon’s official tree and largest timber cash crop, has been declining since Oregon’s drought began in 2012, Buhl said.

Die-offs were first recorded in the driest areas, like south-facing sites, ridges and rocky areas.

“Now, we’re seeing Doug fir dying in other areas where maybe they could have lived before,” Buhl said. That includes throughout the Willamette Valley.

Tree mortality has dropped a bit in the past couple of years, Buhl said.

“But we are still technically in a drought and losing more Douglas fir than historically,” she said. “It’s so widespread and becoming so obvious to people.”

Hike the ‘shortcut’:To Iron Mountain’s stunning summit and wildflower meadows

Grand fir has been declining for years, especially in the Willamette Valley, as precipitation becomes less consistent.

“We might get a dump of water one day, and nothing for a week,” Buhl said. “At a certain point in size these grand firs reach, they can’t withstand that any longer.”

Many people notice insect damage on grand fir, and assume it caused the tree to die, Buhl said. But that’s usually secondary, after drought kills the tree.

Western red cedar has been declining in areas from Oregon through Washington and western Canada.

The Oregon Department of Forestry and Oregon State University are establishing monitoring sites to identify potential causes, which may include drought.

Oregon Desert Trail:750-mile trail brings solitude, canyons and lots of hot springs

Bigleaf maple is showing dieback and leaf damage in various locations in western Oregon.

The Oregon Department of Forestry and the U.S. Forest Service are investigating the cause, which may include drought.

Even if Oregon’s drought ends, some trees won’t recover, Buhl said.

“Trees require more than one year of good rain to bounce back,” she said. “It may be permanent.”

Contact the reporter at tloew@statesmanjournal.com, 503-399-6779 or follow at Twitter.com/Tracy_Loew