Structure and function of soil fauna communities in Amazonian anthropogenic and natural ecosystems

The soil biological conditions of two 5-year-old polyculture tree plantations in Amazonia were studied comparatively to a 13-year-old secondary forest and a nearby undisturbed primary forest. The polycultures had been planted to regenerate the soil degraded by land preparation and a former rubber tree monoculture. Abundance and biomass of functional groups of soil meso- and macrofauna were measured at three-months-intervals over 2 years and litterbag experiments with fauna exclusion were carried out. This paper concentrates on the description of the structure of the soil fauna communities, forming the background for an evaluation of the decomposition processes in polyculture plantations. Decomposition rates were strongly determined by the macrofauna particularly in primary forest, where large earthworms, termites and ants dominated the soil fauna. In the plantations, where litter originated predominantly from the non-planted, adventitious vegetation, an abundant decomposer fauna was found, in which however other groups or species dominated. Although decomposition rates in the plantations were about 60 % lower and soil biological variables like organic matter-, nitrogen-content and water holding capacity were slightly lower than in the primary forest, conditions seem favourable for a manipulation of the soil fauna by management of secondary vegetation and litter quantities.