Document: DAV-3-93-8

Linking patch-scale heterogeneity to hillslope runoff in semaird ecosystems.

BRESHEARS, D.D.* ¹, S.N.MARTENS ² and P.C.BEESON ¹

Los Alamos National Laboratory, Los Alamos, NM 87545 USA ¹
University of California Davis, Davis, CA USA ²

Abstract:
Runoff and erosion at hillslope scales is a driver for many environmental problems in semiarid environments. Redistribution of runoff also provides a means of increasing the amount of water available to plants by concentrating the resource at patch scales. Lacking is an understanding of the relationships between patch-scale cover and hillslope runoff. We used a spatially explicit hyrdological model, SPLASH, to evaluate relationships between patch heterogeneity and hillslope-scale runoff by varying the proportions of the vegetation patch types: canopy patches beneath trees, intercanopy patches with bare cover, and intercanopy patches with herbaceous cover. Our objectives were to estimate runoff and runon for each patch type as a function of changing vegetation cover, to evaluate how optimum runon to herbaceous patches depends on the proportion of bare patches, and to assess the sensitivity of hillslope runoff to changes in cover. We parameterized SPLASH for the Mesita del Buey Pinyon-Juniper Woodland Site at Los Alamos, NM using grid cells of 1 m by 1m over and area of roughly 100 m by 150 m. We initially evaluated these relationships for an intense 1 cm convective storm. Bare patches generated net runoff whereas canopy and herbaceous patches were sources for capturing runon. Herbaceous patches received optimum runon at intermediate values of cover for bare patches. Hillslope runoff was not sensitive to initial reductions in % bare cover, but then increased with increasing % bare cover. These simulation results are consistent with observations of runoff at patch and hillslope scales and demonstrate how patch patterns in cover are integrated with hillslope runoff. The results have important implications for assessing how changes in vegetation can trigger a transition from low to high erosion rates.

Keywords: scale, runoff, pinyon juniper woodland, semiarid ecosystems

This abstract is being presented at: 9:45 AM in session:
Oral Session #58: Landscape Ecology.