NATURAL VARIABILITY OF VEGETATION, SOILS, AND PHYSIOGRAPHY IN THE BRISTLECONE-PINE FORESTS OF THE ROCKY-MOUNTAINS

Pinus aristata Engelm. forest vegetation in Colorado was studied to de termine vegetation composition and the relationship between vegetation and environment. Species percent cover, tree size class, and environm ental variables were recorded for 49 plots. Previously collected data for 4 plots from New Mexico were included. Environmental variables inc luded latitude, longitude, elevation, slope, aspect, topographic posit ion, parent material, percent rock cover, mean rock size, litter depth , estimated plot age class, and evidence of anthropogenic disturbance. Soils were analyzed for texture, depth, and percent carbon and nitrog en. Pinus aristata foliage was analyzed for percent nitrogen and phosp horus. Direct and indirect gradient analyses (CANOCO) were used to det ermine environmental factors associated with community composition. Ve getation in P. aristata forests is influenced primarily by elevation a nd soil pH. Substrate, soil texture, topographic position, and geograp hic location are secondary factors. Six plant associations were identi fied using cluster analysis (listed in an elevational sequence from lo w to high): Pinus aristata / Festuca arizonica Vasey, Pinus aristata / Festuca thurberi Vasey, Pinus aristata / Juniperus communis L., Pinus aristata / Vaccinium myrtilus L., Pinus aristata / Ribes montigenum M cClatchie, and Pinus aristata / Trifolium dasyphyllum Torr. & Gray.