Response of Subalpine Forests to Spruce Beetle Outbreak in Colorado

Age-structure stand analyses and dendrochronological techniques were used to investigate effects of a major spruce beetle (Dendroctonus rufipennis) outbreak on stand composition, tree age, radial growth and plant succession in subalpine forests in the northern Colorado Rocky Mountains. The outbreak, in the 1940s, resulted in a shift in dominance from Engelmann spruce (Picea engelmannii) to subalpine fir (Abies lasiocarpa), a reduction in maximum and average tree diameter, height and age, and reduced establishment of lodgepole pine (Pinus contorta) seedlings. Following the outbreak, suppressed small-diameter spruce and subalpine fir were released; growth rates of released trees remained high for \u3e40 years. This pattern of accelerated growth, rather than new seedling establishment, is contrasted with the effects of fire