Bark Beetles Take a Bite Out of Southcentral
Near Pump Station 12, pipeline mile 736 --- I'm sitting in the woods, on a cushy pad of spruce cones provided by a red squirrel. The spruce tree supporting my back is dead. Dead too, is the spruce tree in front of me. The mountains surrounding me are gray with the skeletons of thousands of former spruce trees. The culprit? The spruce bark beetle.
About the size of a grain of rice, the spruce bark beetle has drastically changed the forest here. I noticed the effects of these tiny insects at my first campsite beyond Thompson Pass -- the tree I used to suspend my food away from bears was a beetle-killed spruce. I'll be witnessing their work for the next several weeks as I hike toward the Alaska Range.
How could such a tiny creature do so much damage? Before I embarked on my journey, I called Ed Holsten, a research entomologist for the U.S. Forest Service in Anchorage, who told me I'd have a hard time finding many beetles here these days. "There is very little beetle activity there," he said, "because beetles have killed most of the large spruce."
The bark beetles first attacked these trees about 10-to-12 years ago, Holsten said. After landing on spruce trees, adult beetles drilled holes about the size of the tip of a ballpoint pen. Under the bark, the beetles laid their eggs, and that's where the trouble began. Once eggs hatch into larvae, they feed on the phloem, the conductive tissue just below tree bark where trees transport nutrients from leaves to roots. Thousands of beetle larvae munch their way through the phloem, killing trees by girdling them from within.
White spruce larger than six inches in diameter seem to be the beetles' preferred targets, Holsten said. A quick look around the woods here confirms that. I see a lot of healthy white spruce, but they're all on the smallish side. And tentside, the black spruce all look to be their healthy, pipe-cleaner selves.
All the beetle-killed trees have dropped their needles. Though the dry trees are already a fire hazard, the real volatile time will be 5-to-10 years from now, Holsten said. That's when these trees will fall and transform the beetle-killed forest into a jumbled wood pile.
On the Kenai Peninsula, where the bark beetle ravaged during the 1980's and early 1990's, forest workers measured two tons of woody debris per acre when the bark beetle infestation began. After the attack, fallen dead spruce on the Kenai upped the woody-debris-per-acre total to 40 tons.
Though Alaska has experienced bark-beetle outbreaks for as long as Alaska has had spruce trees, the current bark-beetle damage seems worse than ever before, Holsten said. "In the 1920's, beetles infested more than 200,000 acres near McCarthy, with only about 20-to-30 percent of the spruce killed," he said. "Today's stands in the Copper River area are 80-to-90 percent wiped out."
What has changed?
Weather records show that temperatures in the Copper River valley have climbed slightly in the past 80 years, and the recent warmer weather could be more suitable for bark-beetle survival.
"The warmer it gets, the better it is for them to do their thing," Holsten said.
