Pine Beetle Drama
What’s red and dry and dead all over? Pine forests throughout western North America, that’s what. (If you said itchy, flaky skin, you’d be wrong… and kinda gross.) The western slopes of the Rockies are undergoing what’s been called the largest landscape change since the Ice Age. And it’s all thanks to a little beetle that’s no larger than your pinky fingernail.
The Mountain Pine Beetle (or MPB) is a small black beetle that looks, well, like a beetle. MPBs swarm pine trees, and bore into the bark to lay eggs–each female lays 60 to 75 eggs. Not only do MPB larvae munch their way through the important bits of the tree trunk (the xylem and phloem cells responsible for water and nutrient transport) but they also introduce a blue fungus that knocks out whatever xylem and phloem tissue the larvae miss. With no way to shuttle water and nutrients from one part of the tree to another, the pine tree becomes red, dry and dies within a year. The death of one tree is no big deal, but millions and millions of acres worth of dead trees…That’s a slightly bigger problem. Scientists estimate that 90% of British Columbian pine forests will be red, dry and dead in just eight years.
Stories of seemingly insignificant animals bringing entire ecosystems to their knees are pretty common these days. Zebra mussels are modifying the Great Lakes. Cane toads are transforming the Australian outback. Zebra mussels and cane toads are invasive species–animals introduced into an ecosystem where they don’t belong. But our little western agent of change, the MPB, is a local. In fact, it’s been on this continent longer than humans have.
Hmmm…If MPBs have been here all along, why the sudden drama? The answer: Smokey the Bear’s done too good of a job limiting forest fires–oh, and climate change is to blame, too.
Beetles primarily attack mature pine trees (FYI: Lodgepole pines are mature at 80 years), but they can also take out weakened or unhealthy stands of pine. Before Smokey started enlisting you “to help prevent forest fires,” periodic fires kept the forest thin and the concentration of mature trees low. Our forest fire fighting efforts have kept this natural process at bay, setting the table for an MPB buffet.
And then there’s the whole climate change thing.
After hatching, the larvae spend the next ten months overwintering in the tree trunk. Apart from predators like parasitic wasps and woodpeckers, the biggest threat to MPB larvae is a cold snap. When winter temps fall below -35°C (-31°F) for several days in a row, the bitter cold kills off most of the larvae in the tree trunks. Sans cold snap, however, the larvae keep chowing on the dying tree until they pupate and emerge in early summer as the next generation of MPB ready to fly off and find a new tree to kill. As more larvae survive the warmer winters, the MPB population grows with each successive generation-as does the population’s tree-killing potential.
Thanks to higher numbers (and warmer winters) MPBs are crossing the Rockies–a geographic boundary that used to quarantine the little buggers in the west. And, if it keeps getting warmer, the northern Boreal Forest that stretches from Alaska to northern Québec could be the beetles’ next dinner destination.
That would be bad. It would be bad because we don’t want to lose the Boreal Forest to an infestation of voracious beetles-obviously. But that’s just the tip of the badness. You see, in a “normal” situation, MPBs curb their own population by eating themselves out of house and home. (They eat all of the mature trees, then move onto the smaller trees, but the small trees die quickly and leave the larvae homeless. Homeless larvae can’t survive the winter and thus endeth the MPB outbreak.) There are a lot of trees in the Boreal Forest-enough mature trees to keep the MPBs happily munching for a long, long time. They could munch their way east and then they could munch their way south-and then west and north and east and south. And that would be bad.