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Something is killing bigleaf maples — Washington’s biggest broadleaf tree — and scientists can’t stop it. They don’t even know what’s causing it.

“We’ve looked for everything we can possibly think of and what people smarter than us can think of,” said Amy Ramsey, a forest pathologist with the state Department of Natural Resources.

From British Columbia to California, stands of bigleaf maples are dying, leaving bald patches in the forest canopy or even denuded hillsides.

Reports of dying and dead maples first reached the DNR in 2010, Ramsey said. Foresters noticed the trees were producing small, scorched-looking leaves or none at all. Sometimes, the crown — the upper most branches of the tree — would die.

The reports, from forest professionals, were scattered at first. Then the public began to call.

“The public had questions, and we didn’t have answers,” Ramsey said.

When the DNR began to survey state forests, it found the problem was widespread.

Since then, the number of trees affected has grown.

Several agencies — including the DNR, the U.S. Forest Service and the University of Washington — have been studying the maples but no diseases or insects have been found in significant numbers to be a culprit.

“It is still a mystery,” Ramsey said.

Grand dame of the forest

Take a drive along Point Defiance Park’s Five Mile Drive and you’ll find plenty of big, healthy bigleaf maples with huge green leaves.

But across the road from the park’s new Pacific Seas Aquarium and next to a foot bridge is a sickly looking bigleaf. Some branches are bare. Others have shrunken leaves. Some of the leaves are scorched — green in the middle, dead and dry on the margins.

It’s a classic look for the mysterious ailment. This tree has been dying for several years. Several of its trunks were recently cut back after their crowns died, said Mark McDonough, Metro Parks Tacoma urban forester.

“There was just a tremendous amount of dead wood over that pathway, so I had a contractor come in,” he said.

McDonough has noticed declining health in many of the trees under the jurisdiction of Metro Parks for the past three years, but not a disproportionate number of maples.

The situation at Woodard Bay Natural Resources Conservation Area north of Olympia is more dire. There, hundreds of bigleafs in various states of illness stand along the waters and among healthy conifers.

Some trees have been dead for years. Others, their leaves small and yellow, stand side by side with healthy maples.

Personnel at Thurston County Parks have seen increased deaths of bigleaf maples, said spokesman Bryan Dominique. A large maple will soon be felled at Kenneydell Park, he said.

The loss of the big maples is about more than just losing a majestic tree.

Whether they’re at Point Defiance or draped with moss in the Hoh Rainforest, bigleaf maples are so large they support a virtual bed and breakfast for creatures.

Licorice ferns grow on its branches, birds nest in cavities and creatures crawl in the litter of its leaves on the forest floor, said Ken Bevis, a stewardship wildlife biologist with the DNR.

Pollinators thrive on its flowers, and animals eat its seeds. The trees provide much needed shade for salmon-bearing streams, Bevis said.

The tree is also valuable to people.

Although the tree isn’t grown for timber, it is used for everything from cabinetry to piano frames. Burls of the tree — where the wood grain moves in whorls — are so valuable that maple poachers are a problem in parts of Washington.

‘They were all dying’

Fall is just days away, and soon leaves of deciduous trees like the maple will turn yellow and drop. Some trees will die from old age —the natural succession of the forest.

Those characteristics would make it easy for a new disease to affect the maple and go unnoticed for years.

The hunt for a killer

The Forest Service and the DNR launched intensive research in 2011. Ramsey and other researchers ran through the list of usual suspects in forest pathology over several years. But one by one, suspects (verticillium wilt, bacteria, root rot, beetles, blight, leaf hoppers) were crossed off the list.

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Out-of-state researchers think Washington is the hardest hit state, Ramsey said, but she is skeptical.

One thing is certain, she said: The maple decline keeps getting worse.

“We’ve seen increased mortality in the bigleaf maple and increased damage every year,” she said.

“The symptoms aren’t unusual in the trees,” said Jake Betzen, a graduate student at the University of Washington’s School of Environmental and Forest Sciences. “It’s unusual in the sense that all these trees are dying.”

Going forward

Betzen isn’t expecting to find an exotic killer lurking in the forests. He thinks the culprit could be more prosaic.

“I think this is the new frontier of a lot of environmental and forest health,” he said. “The world is changing around us.”

Those changes include climate and increased urbanization.

“I think we’re going to see more and more changes in the forest, and this is one of the way changes present themselves,” he said.

Ramsey concurs.

“They are going to be the canary in the coal mine,” she said of the bigleafs and other trees. “They are going to be the first indication of climate change.”

Meanwhile, near Randle, Patty Vance has no more healthy and mature maples on her property.

“They’re all in some sort of decline,” she said.

She has advice for city dwellers.

“I would think twice before having a big maple in my front yard as an ornamental tree,” she said. “You fall in love with it. You wouldn’t want it to just die.”

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