Bedford, David R听1听;听Small, Eric E听2听;听Tucker, Greg E听3
1听USGS, Department of Geological Sciences University of Colorado
2听Department of Geological Sciences University of Colorado
3听Department of Geological Sciences University of Colorado
The soil properties under vegetation have long been observed to be different than soil in non-vegetated (bare) areas. In order to assess how vegetation affects soils and runoff processes, we have been studying a grassland and shrubland in central New Mexico and a shrubland in southern California. We have determined the magnitude and scale of soil property heterogeneity associated with vegetation and how it affects overland flow and infiltration. We have found that the small-scale soil property heterogeneity is strongly determined by the type of vegetation, and the soil-geomorphic context, specifically type of and position within landforms. In all cases, we found that soil properties are different under vegetation and change with distance from vegetation canopy. However, the magnitude and scale of soil heterogeneity is determined by landform type, and often the position with in a landform. We have then investigated how small-scale heterogeneity of soil properties affects overland flow and infiltration using runoff plot observations and a numerical model. We have found that in addition to rainfall intensity, the nature of the vegetation-soil patterns can dramatically alter predictions of runoff. In grasslands, microtopography has the strongest control on runoff due to depression storage. In shrubland alluvial fans and steep hillslopes of New Mexico, both microtopography and infiltration heterogeneity affect runoff, but have the same relative impact. Preliminary results from a southern California shrubland suggest that larger scales of soil heterogeneity result in stronger control of small-scale heterogeneity on runoff. Further preliminary results suggest that the spatial dynamics of overland flow varies greatly with vegetation type and landform characteristics.