Spatial analysis of selected soil attributes across an alpine topographic/snow gradient

The impact of the topographic/snow gradient on soil processes in alpine tundra on Niwot Ridge of the Colorado Front Range (Rocky mts, USA) was assessed using geostatistical modeling and a fractal approach. The mean snow depth, which measured between 1984 and 2000, exhibited a smooth spatial continuity across the study grid area (550 × 400 meter). Soil color variables showed a nested structure that was attributed to a confounded effect of various soil-forming factors on catenary processes. The spatial structure of texture classes exhibited no spatial structure and was explained by data sparsity, cryoturbation, and biological processes that mask the expected long-distance variations (i.e., 550-m) of the catenary processes. Organic C, pH, bulk density, and soil moisture content showed various degrees of spatial continuity, but all indicated that the topographic/snow gradient is not the only dominant soil-forming factor in this alpine ecosystem. The estimated fractal dimension D for the grid landform and the mean snow depth varied between 1.2 and 1.4, indicating that they vary smoothly with long-range variation. The estimated D of the soil variables ranged between 1.6 and 1.8, showing a noisy appearance with short-range variations. These results strongly suggest that most small and micro-scale variations in the alpine soil environs resulted from the combined effect of cryoturbation, biological activity, parent-material and eolian deposition, whereas the large-scale variations originated as a result of the topographic/snow gradient.