Beetles and Severe Fire: Who’s on First? A Century of Disturbance in Colorado’s Subalpine Forests

Forests have evolved with and depend on natural cycles of wildfire, insect outbreaks, disease, and extreme weather for periodic rejuvenation. The subalpine forests of northwestern Colorado experienced an unusual sequence of disturbances in succession over the past 125 years. Severe wildfi res in 2002 were preceded by stand-replacing fi res a century before. These were followed by a record setting wind blowdown, subsequent salvage logging, and two separate bark beetle infestations. This study by University of Colorado researchers was the first to collectively analyze how a century of disturbances interacted with each other to shape ecosystem patterns and processes with regard to fire risk in this forest type. The project evaluated the extent and severity of the wildfi res that took place in northwestern Colorado during the extreme drought of 2002 in relationship to the disturbances that took place during the five years prior to the fires, and to the stand-replacing fires of the late 19th century. Many of the findings were quite unexpected. The most surprising result was that neither bark beetle infestation nor salvage logging had detectable effects on fi re severity or extent. Increased risk of fi re was attributed to drought