By Ned Rozell
April 19, 2007
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.