Beetles, bears and ecosystem scares
February 1, 2007
p. What do beetles, bears and rising atmospheric carbon dioxide levels have in common? In the Rocky Mountains, the three are intricately linked in what might become a major ecological disaster for North America’s pine forests. The mountain pine beetle is spreading through the higher-altitude whitebark pines, threatening the trees and the entire eco-systems that depend on them.
p. Also known as pine bark beetles, the insects are commonly found in lodgepole and ponderosa pine, and have taken advantage of the slight increase in temperatures and have expanded their range into the Rocky Mountains’ higher altitudes. The females burrow into the pine bark to deposit their eggs and the spores of a fungus that eventually kills the tree after the beetles have moved on to new prey.
p. In the early stages of infection, the trees appear healthy, except for small holes in the bark from the burrowing females. However, according to research from Colorado State, while the larvae grow and track through the phloem feeding, a bluestain fungus cuts off the flow of sap through the tree, helping the beetles feed off the trees. The larvae spend the winter under the bark, and the adults emerge in mid-to-late summer to move on and infect new trees. The pine slowly dies from the fungal infection after the beetles have gone, turning a characteristic rust-red color.
p. Dr. Jesse Logan, a beetle expert from the US Forest Service, told The New York Times that once a tree is infected by the mountain pine beetle, the tree’s death is inevitable. In the Rockies, 143,000 acres are already infected. “These are true predators,” Logan said. “They have to kill to reproduce. Most other bark beetles don’t do that.”
p. But what does a spreading wave of beetles and rusty, dying trees have to do with the grizzly bear population? Although, according to Wikipedia.com, the bears have been on the threatened and endangered species lists in the United States and Canada, respectively, recent population increases mean that they might be taken off the lists in the near future. Cutting protections now could be detrimental to the bears, Logan said, because their habitats are at risk from the spreading mountain beetles.
p. We think of bears as classic omnivores — predators eating other wild mammals and occasional campers — but with more refined tastes as well, catching salmon and munching on nuts and blueberries. In fact, these food sources change with the seasons, and in the fall, the bears depend on pine-nuts for a high fat intake before the winter hibernation. With dying strands of Lodgepole and Whitebark pines across the mountains, there will be less food available for the grizzlies during the leaner fall season.
p. Right now, there are still regions of higher altitude where the voracious beetles have been unable to establish, the cooler temperatures blocking their natural reproductive cycles.
p. It might be only a matter of time before further temperature increases allow the beetles to climb higher. They required a less-than-two-degree-Fahrenheit increase to begin using whitebark pines, and current global climate change estimates are predicting a much greater increase in the century to come. The beetles might push the bears up the mountain, if trying to find a stable pine-nut supply from healthy tree keeps getting harder. If the trends aren’t reversed, however, Logan and others worry that the grizzlies and beetles might run out of mountaintops to climb.