Spruce Beetles and Fires in the Nineteenth-Century Subalpine Forests of Western Colorado, U.S.A.

Abstract

We analyzed 17 photographs, taken between 1873 and 1915, that illustrate widespread mortality in subalpine forests of western Colorado. Eight of these photographs, reproduced here, contain three general patterns of mortality, interpreted to result from spruce beetle (Dendroctonus rufipennis) attacks, fires, and wind. Tree-ring chronologies at four of the sites corroborated the role of spruce beetle in killing the trees visible in the photographs. The photographs and tree-ring dates suggest that the spruce beetle outbreak occurred between the 1850s and the 1880s, and affected forests from central New Mexico to north-central Colorado. Spruce beetle outbreaks are a significant type of natural disturbance in these forests. The relative contribution of beetles and fires to subalpine forest structure is in need of further research. The sequence and spatial configuration of disturbances by spruce beetles, fire, and wind varies, and can be spatially heterogeneous, even on small land areas. In such areas, forest responses to uniformly applied disturbance controls (e.g., fire suppression) will be spatially heterogeneous, not affecting all parts of the landscape uniformly.