Since the late 1990s, mountain pine beetles have swept through millions of acres of forest in the Rockies, turning hillsides of trees a rusty red and then grey as they populate trees and kill them. In Colorado, this outbreak seems to have peaked in 2008 and 2009; but just as one species slowed, another -- the spruce beetle -- has picked up steam. A new University of Colorado study published in Ecology reveals how drought was the driver of the rise in spruce beetle activity and resulting tree deaths in Colorado's high-elevation forests in recent years. The drought is in turn linked to changes in sea surface temperatures that are expected to continue for decades to come. In the long-term, such massive insect infestations could dramatically diminish North American forests' ability to retain water and sequester carbon — meaning trees will be less effective at balancing out the human toll on the environment.
So far, fewer acres of trees have been affected by spruce beetles than mountain pine beetles, but there are more spruce forests in Colorado than Lodgepole pine, so there's "no reason to expect the percentage mortality to be less or acreage affected to be any less" than it was for the mountain pine beetle epidemic, said Tom Veblen, coauthor of the study and a geography professor at CU.
Lead author Sarah Hart remembers flying over British Colombia in 2007 and seeing endless stretches of red trees killed by mountain pine beetles. When she moved to Colorado, a spruce beetle outbreak had started to turn heads in the area, prompting her to look deeper into its underlying causes.