Soil macrofaunal communities in permanent pastures derived from tropical forest or savanna

Soil macrofauna are sensitive to land use changes and this may have implications to soil functioning. The impact of the conversion of native ecosystems into extensive or intensive pastures on soil macrofauna were assessed with a standardised methodology in two neotropical phytogeographical regions, i.e. a tropical savanna area (Eastern Plains of Colombia) and a tropical rain forest area (Brazilian Amazon). In the savanna area, extensive cattle ranching only led to a slight enhancement of earthworm populations and to short-term fire-induced decreases of macrofaunal density. In intensive pastures, the initial taxonomic richness and composition of soil macrofauna were maintained, while native earthworm biomass was strongly increased. This may be explained by the similar mesologic conditions between these systems (similar vegetation structure) and by the higher quality of the organic inputs in the pastures (roots, litter and cattle faeces). Increased macrofaunal activity with a high taxonomic diversity is expected to have positive impacts on the sustainability of pastures in Colombian savannas. In the Amazon basin, slashing and burning of the forest for intensive pasture establishment resulted in more dramatic effects on native macrofauna. Taxonomic diversity was particularly strongly affected. Native earthworm species were largely depleted at the expanse of exotic peregrine species like, e.g. Pontoscolex corethrurus. These results are probably bound to the deep environmental changes that follow the conversion of forest into grassland ecosystems. Such modifications of macrofaunal communities are known to have potential negative effects on soil functioning and on the sustainability of agropastoral systems in this area. (C) 2004 Elsevier B.V. All rights reserved.