New Mexico Geological Society Annual Spring Meeting — Abstracts

Distinct contrasts in vegetation are affected by slope aspect-related microclimatic factors. The initial driving force for these contrasts is the variation in solar radiation, with north-facing slopes receiving less winter sunlight than south-facing slopes. However, an investigation of vegetation, soils and microtopography on opposing slopes of a small drainage basin suggests that internal factors may enhance the contrast through system feedback mechanisms that influence soil moisture availability. In the study area, south-facing slopes support scattered creosote bush with 15% black grarna grass cover, while north-facing slopes support scattered one-seed juniper with 30% black grama cover. Soils on the North facing slopes are significantly finer, have more calcium carbonate and more organic carbon. Microtopography and surface runoff features suggest that greater vegetation density and closer spacing of flow barriers on north-facing slopes help to dissipate runoff energy, retaining both surface water and fine materials and hence, enhancing plant production. Thus, while initially the vegetation contrast may result from exogenic factors (such as solar radiation), the degree of contrast may actually be enhanced through time because of endogenic feedback mechanisms between vegetation, pedogenesis and the evolution of surface microtopography.