SPATIAL VARIATION IN TREE REGENERATION IN THE FOREST-TUNDRA ECOTONE, ROCKY-MOUNTAIN NATIONAL-PARK, COLORADO

Ecotone vegetation may be especially sensitive to climate change. In p articular, the invasion of subalpine meadows by tree seedlings has bee n well documented. However, there has been no systematic analysis of t ree regeneration across the environmental heterogeneity of the alpine forest-tundra ecotone (FTE). Also, the position of the FTE may be reli ctual from more favorable climates of the past and therefore unrespons ive to changing climate. To assess the environmental controls on FTE t ree regeneration, to determine whether the ecotone might be relictual, and to determine whether tree invasion of nonforested FTE areas is oc curring, we measured tree regeneration in various environments within the FTE of Rocky Mountain National Park, Colorado. Generally, seedling establishment appears to be controlled by patterns of soil moisture. Little seedling establishment was observed in krummholz openings, exce pt for high seedling densities in willow wetlands. Tree seedling invas ion of tundra is rare. Therefore, the upper limits of the FTE in Rocky Mountain National Park may be relictual from more favorable climates of the past. Abundant seedling establishment in patch forest openings suggests that patch forest may be poised to change to closed forest.