The landscape ecology of the Palmer Divide, central Colorado

This study of the landscape ecology of the Palmer Divide integrates geomorphic, soil structure, chemistry and development and climate variables with characteristics of the vegetation mosaic to explain the history and structure of the landscape. The purposes of the study were: (1) to describe geomorphic-soil-climate-vegetation relationships on a regional scale; (2) to identify dominant environmental gradients associated with major vegetation types and; (3) to synthesize interdisciplinary information explaining the present landscape.; The Palmer Divide is located west of the Colorado Front Range between Denver and Colorado Springs. This landform, composed of the Tertiary Dawson and Castle Rock Formations, divides the South Platte and Arkansas River watersheds.; The major vegetation types are Douglas-fir and ponderosa pine forests; juniper-pinyon woodland;, Gambel oak, mountain mahogany deciduous shrubland and, little bluestem, gray prairie dropseed, blue grama and buffalograss grasslands.; Cover data for 165 species in 88 stands was analyzed using DECORANA (detrended correspondence analysis). Canonical correspondence analysis (CANOCO) was used on 17 key stands (135 species) also measured for selected environmental variables. The variables used were: gravel, clay, organic matter, phosphorus, magnesium, B{dollar}sb{lcub}rm t{rcub}{dollar} horizon development, mean solum depth, soil parent material, rock outcrop and snow and radiation indexes. Correlation of the species-environmental variable ordination axes was {dollar}>{dollar}0.92 in the CANOCO analysis.; The first ordination axis (soil moisture) correlated strongly with soil particle size, granitic parent material, total snowfall, the radiation indexe and topographic factors. The second major gradient represented soil development factors (solum depth, B{dollar}sb{lcub}rm t{rcub}{dollar} horizon development, organic matter and phosphorus content). A third gradient related to soil water holding capacity, specifically the presence of clay and silt in deep soil layers. Most of these variables were closely allied with geomorphic history and structure. Abiotic gradients had differential importance for various major vegetation. Soil particle size, particularly the presence of clay, was associated with deciduous shrubland, juniper-pinyon woodland and relict and shortgrass prairie. Microclimate differences caused by slope and aspect was important for Douglas-fir forest.