Influences of fire history and topography on the pattern of a severe wind blowdown in a Colorado subalpine forest

Abstract

1 In 1997, a major windstorm blew down over 10 000 hectares of subalpine forest in Routt National Forest in north-western Colorado. We tested whether fire history and topographic variation, across the landscape, determined subsequent susceptibility to damage from this windstorm. 2 We combined dendrochronological techniques with a geographical information system (GIS) to examine the relationship between the effects of the blowdown and the spatial heterogeneity of the vegetation. We reconstructed the spatial fire history in a c. 4400 ha area by first identifying distinct patches in the landscape on aerial photographs, and then in the field by determining the disturbance history of each patch by dating fire scars, ages of post-fire cohorts and releases of remnant trees. 3 Both topographic position and fire history contribute to susceptibility to wind damage. Stands at higher elevations, on easterly slopes and closer to ridges were most affected. Younger stands (i.e. more recently affected by stand-initiating fires) were less affected particularly in areas affected by low-moderate severity blowdown (< 80% damage). The ecological effects of the very severe 1997 windstorm were mediated by the legacies of fires which occurred several centuries ago. Interactions between natural disturbances, such as fire and blowdown, lead to synergistic effects on forest dynamics, even when disturbance is infrequent.