USING GIS TO MODEL TREE POPULATION PARAMETERS IN THE ROCKY-MOUNTAIN NATIONAL-PARK FOREST-TUNDRA ECOTONE

Climatic change may alter vegetation composition and structure, but th e response to climatic change can be expected to be spatially heteroge neous. Tree populations in the alpine forest-tundra ecotone, for examp le, map find only certain locations to be favourable for regeneration and growth. If monitoring and detection of vegetation responses to cli matic change is to be most successful, the monitoring system must be t uned to the locations where a response is most likely. We used the GRA SS geographical information system (GIS) to map population parameters indicating potential change throughout the forest-tundra ecotone (FTE) of Rocky Mountain National Park (RMNP). Seedling density in patch for est and krummholz openings, as well as annual krummholz height growth, were measured in the field. These parameters were then modelled over the heterogeneity of the FTE environment, using principle components r egression analysis. The GRASS GIS was used to extrapolate the resultin g predictive equations to the entire RMNP FTE. Potential FTE responses to climate change were evaluated in the context of species-specific d ifferences in how tree seedling density and krummholz height growth ar e associated with the present environment. For example, climate change leading towards moister conditions, causing currently xeric environme nts to become more mesic, might increase the spatial extent of existin g tree invasion into patch forest openings. This would increase the po tential for widespread conversion of patch forest to closed forest. Pr esent population parameters extrapolated spatially may provide a usefu l guide to where future change is likely.