Collembola of loess grassland: effects of grazing and landscape on community composition

In loess grasslands, grazing by sheep is responsible for changes in the composition of vegetation and controls on secondary successional processes. Grazing has a very complex effect on the soil by altering its physical, chemical and biological properties, which makes it difficult to distinguish the underlying mechanisms. Landscape heterogeneity also influences soil and vegetation processes, having a greater effect on environmental factors than sheep grazing. To compare the relative effects of sheep grazing and one aspect of landscape heterogeneity on the collembolan community, four valleys with two grazing treatments were selected. The sides of each valley had SW and NE aspects resulting in two types of landscape heterogeneity. In a split-plot experimental design, the effects of grazing pressure and aspect were examined in relation to the relative abundance, species richness, evenness and composition of the collembolan community. Grazing pressure had a positive effect on total abundance and a negative effect on species richness of Collembola. Aspect did not significantly influence total abundance but valley sides exposed to SW had a higher species richness. Grazing changed the dominance structure, reduced the evenness and strongly influenced the composition of the collembolan community. Due to grazing xerotherm epedaphic species disappeared resulting a less diverse Collembola fauna. Aspect had a lesser effect on collembolan community composition than grazing. The results suggest that the diversity of springtails maintained by landscape heterogeneity in loess valley sides is reduced by sheep grazing. Further, differences in soil humidity could not explain the changes in structure and abundance of the collembolan community alone, sheep grazing may drive changes in collembolan community through mechanisms of biotic effects. (C) 2001 Elsevier Science Ltd. All rights reserved.