16 - Dynamics of mountain pine beetle outbreaks

Abstract

Insect disturbance, as suggested in this chapter, is important in maintaining a diverse age structure for lodgepole pine. Left to its own devices, lodgepole would develop into crowded and unhealthy forests of over-mature trees. Although the mountain pine beetle is an aggressive tree killer, it is a native component of natural ecosystems. The forests of the American West have coevolved in ways that incorporate mountain pine beetle disturbance in the natural cycle of forest growth and regeneration. With disturbances such as mountain pine beetles, a certain homeostasis can be maintained, at least on sufficiently large spatial scales. As the model in this chapter illustrates, insect disturbances can move at a self-limiting pace, balancing the rate of forest regeneration. Like fire (with which mountain pine beetle reforestation is associated), mountain pine beetle disturbance must be viewed as a normal and healthy part of ecosystem function on a sufficiently large scale. This chapter helps establish on what scales, both in time and space, an insect disturbance such as that caused by mountain pine beetles can be expected to serve as a useful and normative disturbance.