2010-03-15

What’s Killing the Great
Forests of the American West?

For many years, Diana Six, an entomologist at the University of Montana, planned her field season for the same two to three weeks in July. That’s when her quarry — tiny, black, mountain pine beetles — hatched from the tree they had just killed and swarmed to a new one to start their life cycle again.

Now, says Six, the field rules have changed. Instead of just two weeks, the beetles fly continually from May until October, attacking trees, burrowing in, and laying their eggs for half the year. And that’s not all. The beetles rarely attacked immature trees; now they do so all the time. What’s more, colder temperatures once kept the beetles away from high altitudes, yet now they swarm and kill trees on mountaintops. And in some high places where the beetles had a two-year life cycle because of cold temperatures, it’s decreased to one year.

Such shifts make it an exciting — and unsettling — time to be an entomologist. The growing swath of dead lodgepole and ponderosa pine forest is a grim omen, leaving Six — and many other scientists and residents in the West — concerned that as the climate continues to warm, these destructive changes will intensify.