Forest Regeneration Above Tree Limit Depressed by Fire in the Colorado Front Range

Abstract

SHANKMAN, DAVID (Department of Geography, University of Colorado, Boulder, CO 80309) AND CHRISTOPHER DALY (Systems Applications, Inc., 101 Lucas Valley Road, San Rafael, CA 94903). Forest regeneration above tree limit depressed by fire in the Colorado Front Range. Bull. Torrey Bot. Club 115: 272-279. 1988.-Tree regeneration was investigated on six sites disturbed by fire at and immediately below the upper altitudinal tree limit in the Colorado Front Range. Before disturbance, the sites with greatest topographic shelter were dominated by Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa). The most xeric sites were dominated by limber pine (Pinus flexilis). High intersite variability in regeneration rates and population densities suggest that early forest stand development was not closely related to elapsed time since disturbance, but varied depending upon topography. Among the xeric sites that were regenerating, limber pine was among the most frequently noted species. Conversely, Engelmann spruce, and to a lesser extent subalpine fir, were found with highest densities on the less xeric sites. In general, these patterns of establishment are consistent with those noted in other studies of forest stand development at lower altitudes in the subalpine forest of the Colorado Front Range. Two of the burned sites were not regenerating. It is hypothesized that lack of seed caching by Clark's Nutcracker (Nucifraga columbiana), the primary seed disperser for limber pine, was limiting colonization of these sites. All sites were at an early stage of successional development, and a forest canopy cover had not yet developed. Rates of regeneration suggest that in most cases the tree limit will return to its former altitudinal position. However, it may be several centuries before these sites develop stands similar to those that existed before disturbance.