SPATIAL VARIABILITY OF RADIAL GROWTH IN THE FOREST-TUNDRA ECOTONE OF ROCKY-MOUNTAIN NATIONAL-PARK, COLORADO

Radial growth in trees has often been used to measure the relationship between climate and tree growth. Variation in radial growth with resp ect to environmental variables may indicate how trees in diverse lands capes may respond to climate change. The purpose of this study is to d etermine whether radial growth is spatially heterogeneous throughout t he forest-tundra ecotone of Rocky Mountain National Park and whether t his spatial variability can be related to environmental variables. Inc rement cores were taken from 5-10 of the largest trees in 59 sampling locations distributed across the forest-tundra ecotone of Rocky Mounta in National Park Mean annual ring width for 1978-1987 was measured in the laboratory. Stepwise weighted least squares Linear regression was used to relate mean annual growth to 25 environmental variables measur ed at each sampling location. Mean radial growth is higher at sampling locations with higher soil pH values and where there is small rock ma terial but varies with zone and associated shrub species. When all sta tistically significant variables are considered, radial growth is slow est in the krummholz zone, intermediate in the patch forest zone, and fastest in the closed forest zone. Within each zone, the presence of J uniperus communis indicates slow radial growth, Vaccinium spp. indicat e intermediate radial growth, and Salix spp. indicate rapid radial gro wth. These results differ from previous studies of vertical seedling l eader growth in the FTE, which found higher rates of growth in the kru mmholz zone. Differing rates of radial and vertical growth may reflect different settings or different responses, though both may indicate t ree ''success.''