Big-leaf maples are dying -- and the cause is a mystery

KIRO 7 launched a drone on Thursday to get a closer look at a wildlife mystery than even scientists have been able to see.

Big-leaf maple trees are dying up and down the West Coast, from British Columbia all the way down to Northern California, and no one really knows why.

The dieback alarms Amy Ramsey, a forest pathologist for the Washington State Department of Natural Resources.

Ramsey took a KIRO 7 crew to the Woodard Bay Conservation Area in Olympia, where big-leaf maples of all ages and sizes are dying.

“This big-leaf maple issue is something that I’ve been working on for a long time,” Ramsey said, while pointing out dead and dying trees, whose brown-tinted leaves are much smaller than normal. “We really haven’t been able to figure out why.”

According to Ramsey, the dieback was first noticed about 20 years ago.

In the past 10 years, however, the problem has become much worse, so the DNR recently secured funding to conduct experiments.

“We started going down the list of different agents we could think of,” Ramsey said. “Different root diseases, microscopic root diseases, different stem diseases, different insects, insects in the leaves, insects in the stems -- and we didn’t find evidence of any of those things.”

Jake Betzen, a graduate student at the University of Washington, is working with Ramsey to try and figure out what is killing big-leaf maples.

Betzen told KIRO 7 that, since no biological factor seems to be the cause, it could be environmental, perhaps even climate related.

“Some of the major things might be the recent droughts.  It’s getting warmer and drier in recent years,” Betzen said.  He’s also exploring other possible causes, such as stress caused by roads and development.

Betzen's thesis on big-leaf maple decline is due by the end of the year but, by then, he and Ramsey still might not have any definitive answers.

Ramsey, who has spent her career studying dead and dying trees, said, "This is one of the biggest issues I’ve worked on regarding tree mortality and I’m sort of head-scratching about why it’s happening.”

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