Troubled Trees

Scientists look for source of notoriously strong yellow cedars' demise

Posted: Sunday, January 07, 2007

With yellow cedars dying at alarming rates, some scientists are trying to find ways to harness the power of the strongest Alaska trees.

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The cedars, which have been used for centuries by Alaska Natives for totem poles and canoes, are now thought to contain oils that could be used to repel mosquitos and other pests.

In chip form, the tree also could help prevent the spread of sudden oak death - a disease that has killed thousands of trees in California.

Yellow cedar (Chamaecyparis nootkatensis ) is highly valued as a timber product and is often used by engineers for hardy structures such as bridges and building beams, said U.S. Forest Service scientist Paul Hennon.

Hennon, who is based in Juneau, has done considerable research into the decline in Alaska's yellow cedar stands. For the past 100 years, more than half of the trees within the 500,000 acres of the Tongass National Forest have died, according to the U.S. Forest Service.

Hennon and others have linked the decline to climate change.

With warmer temperatures and lower rates of snowfall in late winter and early spring, some scientists theorize that the tree's shallow roots are being exposed to blasts of cold air, killing them in their prime.

It's the notoriously strong trees' "Achilles heel," Hennon said. He said it's particularly surprising considering the tree's natural defenses against decay.

When yellow cedars die, they can remain standing for decades without decaying. The reason has been attributed to the composition of oils and their compounds within the tree's core, the "heartwood," which are slowly altered after the tree dies.

U.S. Forest Service scientist Rick Kelsey, based in Corvallis, Ore., said it was only common sense to explore whether any practical use could be found for the hyper-defensive trees.

"It is kind of like a no-brainer in some regards. The snags remain fairly decay resistant until 80 years after they die," he said.

Southeast Alaska's coastlines are dotted with yellow cedar snags, but living trees can be found on coastlines from northern California to Prince William Sound. They are somewhat rare in the Juneau area.

They also are ancient. Yellow cedars coexisted with dinosaurs, Hennon said.

Kelsey's studies have focused primarily on the heartwood, which makes up the tree's strength and contains the defensive essential oils.

Kelsey and his team in Corvallis isolated more than a dozen essential oil compounds in varying concentrations.

They include nootkatin, tropolone and carvacrol. Some of these can be found in everyday food such as oregano and thyme. The names are derived from the scientific name for yellow cedar.

Nootkatin and carvacrol were found to kill spores of Phytophthora ramorum, the mold that causes sudden oak death, a disease that has ravaged forests in California, killing thousands of native oak and tanoak trees.

It is a relatively new and somewhat mysterious tree disease that has not reached Alaska but has a high potential to spread. Doing so could be disastrous both economically and environmentally, Kelsey said.

Kelsey and his research team looked at seven different species of western U.S. conifers to determine if they could harness the decay-resistant oils that protect the yellow cedar.

Tests proved positive. Kelsey believes that if chips were spread beneath a diseased tree, it would destroy the mold spores. Since the spores can potentially spread to unexposed areas on the soles of hikers near diseased trees, chips could possibly be dispersed on highly trafficked areas.

Yellow cedar chips have not been tested, but Kelsey said it is likely chips from that tree could be similarly used.

There is one catch, however - the yellow cedars that are dying are primarily in Alaska.

"The problem with having it all in Alaska is you have to pay transportation expenses," Kelsey said.

Utilizing the dead stands of yellow cedar has some other problems too - many related to expenses of extracting the oils.

"The problem is whether or not they would actually extract these materials from the tree. It is usually not cost-effective," Rick Kelsey said. For example, research by another Corvallis federal scientist, Joseph Karchesy, has shown that the compound nootkatin could be used to as a flea, tick or even mosquito repellent.

"For Joe's stuff, they are actually attempting to develop products for flea and tick repellents and toxins," Kelsey said. "They have also looked at it against mosquitos. He just received a patent for that activity."

Hennon said that often, a compound might be found in a natural product then later reproduced synthetically. This happened with the drug Taxol, which was derived from a compound discovered in the Pacific yew tree, Taxus brevifolia, a slow-growing tree in the Pacific Northwest.

The drug proved extremely effective for fighting breast cancer, but was also controversial because it would take six 100-year-old Pacific yew trees to treat just one patient. A synthetic version was discovered and released by Bristol-Myers Squibb in 1993.

Sometimes, compounds can be found duplicated in other parts of nature. Nootkatin has been found to also occur in the oil from grapefruit, which has come as a surprise to some.

"I don't even know what to think of that, " Hennon said. "They are unrelated organisms. Cedars are ancient trees, but citrus trees are highly evolved."

This could be good news, however, as extracting the compound from a tree is typically more expensive.

"You would never go to the tree to extract it, you would obtain it from the grapefruit industry because they produce it in bulk," Kelsey said.

Research on yellow cedar is also important because it provides the background for management decisions, Hennon said. Learning more about the potential uses of yellow cedar as it is experiencing its natural decline will help them make better choices.

"There is a potential to shift more of the timber harvest from our live trees to our dead trees. They remain healthy for a long time," Hennon said.

• Brittany Retherford can be reached at

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