April 19, 2007
Thursday

The tamarack is one of Alaska's prettiest and most endangered trees. An insect outbreak in the past decade killed up to 80 percent of the adult trees in the state and scientists are keeping an eye on tamaracks to see if they'll need to resort to "genetic conservation," removing small trees from the forest so some will exist in the future.

Tamaracks are trees that look like spruce, but they have cones that sit upright on supple branches. Unlike spruce trees, tamaracks drop their needles every fall. When autumn arrives, tamarack needles change from green to gold before shedding like a dog's fur onto the forest floor. Each spring, new green needles emerge like the legs of spiders from branch nodules. Tamaracks grow on boggy ground in valleys of the Koyukuk, Yukon, Tanana, and Kuskokwim river drainages and foresters say the wood is similar to birch in terms of heating value per cord.

A tamarack tree killed by the larch sawfly and larch beetle in Fairbanks. Photo by Ned Rozell

Starting in the early 1990s, the larch sawfly started attacking tamaracks over the entire range of the tree, more than one million square acres. By 1996, the sawfly infested almost every tamarack in Alaska, gobbling up the solar panels the tree uses for nourishment.

"It's a losing battle for the tree when you have that many consecutive years of being hammered like that," former U.S. Forest Service Entomologist Ed Holsten said in 1996. "Combine that with the trees growing at the extreme end of their range, and it's hard to recover."

Most tamaracks didn't recover, according to Jim Kruse, an entomologist with the U.S. Forest Service in Fairbanks. Forest Service researchers flew over tamaracks in the Interior last fall when they stood out in the forest because of their golden needles that seem to glow just before the tree sheds them. Kruse and his colleagues are doing a two-year survey on tamaracks to see what shape the trees are in.

"There's not a whole lot of the big ones left," Kruse said. "The larch sawfly and the larch beetle have pretty much finished off up to 80 percent of the tamarack over five inches in diameter."

Larch beetles are attracted to trees stressed by larch sawflies, Kruse said. The beetles drill under the bark to girdle the tree from within.

"They've been finishing off the larger trees after the larch sawfly gets in," Kruse said.

This year's fall survey will help determine whether scientists will have to resort to pulling little tamaracks from the field to preserve the species in Alaska. Kruse said the trees are still putting up a battle, but as healthy young trees mature, they become more attractive to insects.

"Last year we flew over six million acres and we found larch (tamaracks) on 11 percent of that," he said. "The big ones have definitely been hurt, and we're kind of anxious to see if this thing rears its head again as the younger trees get older."

Other tree-insect interactions that Kruse and his colleagues will look at this summer include the spruce budworm, which attacks the tops of spruce trees, and the aspen leaf miner and birch leaf miner. John Lundquist of the Forest Service in Anchorage is looking to see if satellites can help detect outbreaks of the latter two insects.

This column is provided as a public service by the
Geophysical Institute, University of Alaska Fairbanks,
in cooperation with the UAF research community.
Ned Rozell [nrozell@gi.alaska.edu] is a science writer at the institute.


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