Mountain Pine Beetle

May 24th, 2010

The Mountain Pine Beetle, Dendroctonis ponderosea (MPB) is a small wood-boring insect about the size of a grain of rice. It lives in pine and fir forests from the Mexican border up to southern British Columbia. Although one is unlikely to ever see a beetle, the effects of their parasitic relationship are quite visible. The beetle finds a host tree, bores through the bark, feeds on the nutrient supplying inner bark (the cambium) and eventually the female lays a nest of eggs. A two week window is all this opportunistic insects need to starve a tree to death. The first year the trees exhibit rust colored needles. The red needles turn gray and drop to the ground leaving a stand of dead trees.



The MPB is a classic parasite. It is much smaller than its host, it has a high degree of specialization and in order to reproduce it kills its source of nutrients. Each spring the beetles move to a new group of trees to repeat the process. Historically the beetle selected compromised trees, thinning the forest more or less in balance. Once a larger number of trees are compromised the beetles experience a population explosion. With regional forests being stressed by drought and warmer winters the beetles exploited these favorable conditions. The current outbreak is unprecedented in scale, severity and duration. The mortality of hundreds of thousands of acres of forest in a broad geographic region will have severe effects on the environment.



Lag time between infestation and a dead forest is several years. The stands of forests are at an increased susceptibility to massive fires. Although the jury is still out on forest dynamics in regards to the pine beetle, the resulting fires might be part of a positive feedback loop. Warm weather allows a proliferation of beetles, creating more dead wood, which in turn burns creating a warmer climate benefiting the beetle. One hundred year temperature observations from nine western Montana locations show a clear warming trend, one that is two to three times the global average. The rise in seasonal averages and fewer days of frost provide the beetle with an ideal habitat. The severe cold needed to keep the beetles in check is not as frequent as it used to be. Although this cycle may take years to play out, it is the transformation of the forests from a carbon sink to a net source of carbon that we should be aware of.



The fragrant air we so cherish in Montana is kept clean by photosynthesis and the natural exchange of carbon dioxide into oxygen. With fewer trees to produce oxygen the forest transitions to a carbon source. No long a carbon sink, where air is scrubbed for human consumption, the forests add another perturbation in the positive feedback loop of warmer climate. What are our options?
Human intervention is costly and marginally effective. As the forests are part of our region we have to learn to live with these small and powerful pests. The current outbreak of beetle infestation will dramatically change the nature of western Montana. We created the conditions that have allowed the beetle to expand and we now have the challenge of trying to predict the future of our forests. What will species of plant and animal will take advantage of the unique conditions presented by a dying forest?



One logical step is to harvest the dead trees for human use before they combust. The trees can be used for biofuels. The Forest Jobs and Recreation Act is a way of opening up stands of trees compromised by the beetle. The dire prognosis of our forests requires action – the bill as proposed by Senator Tester is a step in the right direction.

Posted in Daily Chronicle