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Monday, October 2, 2023
Oct. 2, 2023

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Delayed mortality expected for Pacific Northwest trees

Experts say effects of drought can take a while to manifest


PORTLAND — The effects of the drought and heat on trees won’t be fully known until next spring, tree experts in Oregon say.

Oregon State University professor and forest health specialist Dave Shaw told The Oregonian/OregonLive that there’s typically delayed mortality associated with drought. But rain is predicted this weekend.

“It will definitely be a good thing for the forests,” Shaw said. “But we won’t really know how the trees did this year until next spring, as we often see delayed mortality associated with drought.”

All of Oregon is experiencing drought ranging from severe to exceptional, the worst category. Leaves on some trees are turning brown instead of the traditional fall colors before falling to the ground.

Extreme conditions like these are often from a combination of unusual random, short-term and natural weather patterns heightened by long-term, human-caused climate change. Scientists have long warned that the weather will get wilder as the world warms.

Climate change has made the West much warmer and drier in the past 30 years. Special calculations are needed to determine how much global warming is to blame, if at all, for a single extreme weather event.

Certified arborist Andrew Craig of Springwater Arboriculture in Milwaukie, Ore., said that when trees lose too many leaves, they can’t get enough energy from sunlight needed to grow and fight off disease.

“The trees start to decline because they are running on reserves,” he said.

He said that big leaf maples in some places are dying, and Hemlocks are struggling with bug infestations and lack of water.

“The Western red cedar is going to disappear in the valley within the next 20 years except for in very protected pockets,” he said. “The drought is killing them.”

He said it’s not just drought from this year, but the cumulative effects of recent years.

“The last five years has been so profound that trees can’t adapt fast enough,” he said.