Forest fire in the mountain ranges of north-eastern British Columbia: a historical perspective

In an effort to sustain biological diversity, it has been proposed that the impacts of forest management approximate the effects of natural disturbances. This study has investigated mountainous sub-boreal spruce (SBSvk) and Engelmann spruce-subalpine fir (ESSFwk2/wc3) biogeoclimatic units in north-eastern British Columbia in an effort to provide information on historical fire regimes. This information may help in the development of forest management plans that better approximate ecological processes. The influence of topography on the spatial and temporal extent of sera! age-class patches and contemporary lightning-caused fires was a primary focus in this study. Natural disturbance patch characteristics were described and estimates were calculated of the periodicity of stand-initiating disturbances. A digital elevation model was constructed for the study area and related to age-class information derived from forest cover data, as well as lightning-caused fire location data for the period of 1950-1992. Results showed strong spatial differences in natural disturbance patch characteristics based on landscape orientation. Patch characteristics for both eastern and western slopes of the Rocky Mountains indicated that current estimates of patch size distributions and the periodicity of stand-replacing disturbances do not well approximate historical landscape patterns for the 100 year period prior to 1950. Topography was revealed to have a strong relationship with age-class patch size on western slopes, but it was only weakly correlated with other patch characteristics on western and eastern slopes. The topographical associations of lightning-caused fires and seral patches were somewhat similar, but could not provide conclusive evidence that fires initiated younger forest patches. The dominance of old- growth forest age-classes in the study landscape provided support for the importance of fine-scale or non-stand replacing natural disturbances in the maintenance of forest structure and composition. Explicit consideration of landscape characteristics is recommended in future attempts to approximate natural disturbances.