Identification, distribution and characteristics of erosion sensitive areas in three different Central Andean ecosystems

Abstract

Interactions between erosion processes and soil and vegetation were studied in the three main ecosystems (i.e. sub-Andean valley, high Andean plateau and inter-Andean valley) in the southern Bolivian Andes. Erosion features such as badlands, dunes and stripped bedrock are widespread and reflect different scales of erosion in time, space and magnitude. The extent of active erosion features has been attributed mainly to land use change but geology and climate are also factors. The principle objective of this study was to characterise Erosion Sensitive Areas (ESAs) or physiographical units that are sensitive to erosion. Soil and vegetation properties provided insight into the relative importance of grazing as opposed to geology and climate in explaining the current extent of active erosion features. Erosion features, soil surface characteristics, biomass and chemical and physical soil properties from 36 sites distributed over 15 representative physiographical units were determined. In the areas that are most sensitive to erosion, the biomass of palatable species, soil organic matter (OM) content and available water (AW) are small and grazing density is low or moderate. The areas with high grazing density have large biomass of palatable species and large organic matter and available water contents. The distribution of the ESAs coincides with a semi-arid climate, low biomass of short grasses and very erodible parent material. Current reductions in grazing intensity do not seem to have resulted in less erosion. This suggests that past grazing history has altered the sensitivity to erosion, and the resilience of certain areas, to such an extent that erosion rates are high despite current low grazing intensity. It also suggests that contemporary degradation processes are not driven by current grazing densities but by climatic and geomorphological factors.