Chapter 6 - Bark Beetles and High-Severity Fires in Rocky Mountain Subalpine Forests

Abstract

The dynamics, structure, and landscape heterogeneity of the lodgepole pine and spruce-fir forests of the Rocky Mountains in the western United States are shaped by wildfires, outbreaks of insects, and the potential interactions between these disturbances. Outbreaks of bark beetles create habitat heterogeneity in forests that can benefit numerous wildlife species. While important questions remain, the best available science indicates that outbreaks of bark beetles do not increase the risk of high-severity fires in lodgepole pine and spruce-fir forests of the Rocky Mountains. Furthermore, the effects of outbreaks are much less important to fire risk than are weather and climate. By contrast, severe wildfires can reduce subsequent susceptibility to outbreaks in both forest types, although the modulating effect of fires on susceptibility to outbreaks may be contingent on current and future climate influences on beetle populations and tree resistances. The current state of knowledge does not support the common assumption that increases in bark beetle activity have resulted in increased wildfire activity. Therefore policy discussions should focus on societal adaptation to the effects of the underlying driving factor of increased tree mortality from insects and from burning: climate warming.