Gradient Analysis of Infiltration and Environmental Variables as Related to Rangeland Vegetation

Rangeland plant communities and the hydrologic cycle associated with them are multivariate in nature and are affected by many interacting biotic and abiotic components. A rotating boom rainfall simulator was used to apply rainfall in three applications (dry run, wet run, and very wet run) to paired 3.05- 10.7-m runoff plots. Representative plant community types were tall-grass, mixed-grass, short-grass prairie, and sagebrush steppe. Indirect gradient analysis was used to summarize relationships between rangeland plant communities, infiltration, and soil variables. Effective terminal infiltration rate (fe) was consistently higher in sagebrush communities. The best coefficient of determination of fe for the pooled data set (144 runoff plots, 24 sites, 10 states) was R2 = 0.45. Infiltration equations which represented rangeland community types (short-grass, mixed-grass, tall-grass, and sagebrush-grass) were more robust (R2 values > 0.71). The inclusion of endemic plant species in the model building process also improved fe rates. For example, in the tall-grass prairie, the inclusion of above-ground indiangrass (Sorghastrum nutans) biomass, an endemic native grass species, and other plants as independent variables increased regression coefficients of determination from 0.71 to 0.82.