CLIMATIC INFLUENCES ON THE GROWTH OF SUB-ALPINE TREES IN THE COLORADOFRONT RANGE

We examined variations in tree growth responses to climatic variations among different tree species and habitat types in the subalpine zone of the Colorado Front Range. We constructed 25 tree ring site chronolo gies (11 of Picea engelmannii, 9 of Abies lasiocarpa, 4 of Pinus conto rta var. latifolia, and 1 of Pinus flexilis) from a series of subalpin e habitats ranging from xeric to wet. To establish tree growth respons es to climatic variation, we used correlation and response function an alyses to compare variations in ring widths with monthly temperature a nd precipitation records. At the driest sites, growth of Picea and Abi es tracked climatic variation similarly. At mesic and wet sites, howev er, these species differed in their responses to climatic variation. T he responses of Pinus contorta, sampled over a narrower range of habit at types, differed from those of Picea and Abies but did not differ am ong sites. Steep environmental gradients in the subalpine zone of the Front Range accounted for most of the observed differences in growth r esponses to climatic variation. Even at adjacent sites that differ onl y slightly in topographic position, tree growth responses to climatic variation were distinct. Interspecific differences in response to clim atic variations generally were less important than site differences. I ntersite differences in tree growth responses to climatic variation ca n be used as indicators of environmental differences among subalpine h abitats.