A record infestation of beetles is turning western
The Christian Science Monitor, April 24, 2008
A beetle about the length of a well-trimmed fingernail may be challenging scientists' projections for global warming.
Forests store large amounts of carbon drawn from the atmosphere, helping Earth keep cool. But an infestation of mountain pine beetles is turning more than 144,000 square miles of woods in
The process has the potential to become a vicious cycle: As the climate warms, it favors more severe outbreaks, and if severe outbreaks increase, that leaves fewer trees to absorb carbon and more emissions as dead trees decompose. Researchers say
"This is very important," acknowledges Tom Veblen, a geographer at the
"It's been known for some time that insects are an important part of the boreal-forest carbon cycle," says Werner Kruz, a scientist at the National Resources Canada's Pacific Forestry Centre in Victoria, British Columbia, who headed the modeling effort. But, he adds, the failure to include bugs' cumulative effect in climate models could be leading researchers to overestimate the amount of human-generated CO2 forests can absorb.
And the outbreak highlights the challenges resource managers face as they try to preserve forest resilience in the face of a changing climate and pressure to exploit timber and mineral resources. Because the beetles stay burrowed underneath the bark, the only known method to control infestations before they get out of hand is to cut down the trees they've killed or the live trees they've infected. It's an approach that raises the hackles of some environmentalists and ecologists alike.
Nor is the challenge limited to North America's boreal forests, adds Olga Krankina, a forest ecologist at
Historically, the outbreaks have run in cycles, notes Allan Carroll, an entomologist with Natural Resources Canada who was part of the modeling project. The results appear in this week's issue of the journal Nature.
The exploding bug population found "a real smorgasbord" to support it, Dr. Carroll says.
Those climate factors have also permitted the beetles to move east through mountain passes once too cold for them to clear. And in the summers, significant numbers of the flying beetles have gotten caught up in thunderstorms, which deposit them on the
This migration comes at a time when some 1,500 scientists from around the world are imploring the Canadian government to preserve large swaths of the country's boreal forests. Last May, they sent a letter to the Canadian government asking it to set aside at least half of the forest's 2.3-million-square-mile expanse and keep it free of industrial development, the balance to be managed sustainably.
The bugs' eastward march is likely to be slow, Carroll suggests. And it could further be slowed by the mix of trees east of the
But control efforts would likely still be needed, he adds. That would mean flying crews into the infested area, cutting down dead and infested trees, and burning them on the spot. The alternative, he says, is watching a "disturbance agent move into a forest that hasn't seen it before ... which could increase the fire risk in the future."
And forest managers are coming around to the idea that it may not be wise to salvage harvest in every circumstance, Dr. Kurz adds. The forest's other benefits, from biodiversity to water and soil conservation, may be better retained from leaving dead trees where they are, especially if they stand along rivers and streams, deep in forests where building access roads would do more ecological harm than the deadfall, or along slopes, where removing trees would lead to serious erosion problems.