Bark Beetle-Induced Forest Mortality in the North American Rocky Mountains

The epidemic of mortality by insects and disease throughout the Northern American Rocky Mountains exceeds previous records both in severity and spatial extent. Beetle attacks weaken trees and introduce blue-stain fungi that induce hydraulic failure leading to mortality. The magnitude of this outbreak spurs predictions of major changes to biogeochemical cycling and hydrologic response, changes in species assemblages, and increased wildfire risk. Review of emerging empirical studies reveals conflicting evidence of changes and limited environmental threats. However, widespread forest mortality generates net economic costs and losses by reducing or eliminating market and nonmarket value. Potential deadfall may threaten human life and infrastructure and add costs of programs for hazard-tree reduction. Although forest regeneration following insect epidemics indicates resilient ecological systems, synergistic interactions of beetle kill with other disturbance processes, exacerbated by warming temperatures and drought may stimulate longer-term environmental concerns.