Open Access

Elizabeth N. Franklin, José Wellington Morais, Evanira M. R. dos Santos

• The mesofauna communities were assessed every three months (June 1997 to March 1999), in the litter and soil of a polyculture system (POA and POC) and from a primary (FLO) and a secondary (SEC) forest. The highest densities were obtained in POA, due to the dominance of Oribatida. The densities of Acari Oribatida and Collembola were notably lower in the mineral soil. For non-Oribatid Acari, the same tendency was not clearly detected. In contrary to the other groups, the highest densities of Collembola were found in FLO. In general, densities in the litter layer were higher. Therefore, strong differences were detected between 1997, an exceptionally dry year caused by the ”EI Niño” Southern Oscillation, and 1998. The mesofauna population was lowest in 1997 Only in 1997, was the density in FLO, POA and POC higher in the soil fraction. The pattern in SEC was not the same because of the higher amount of litter. We hypothesized that the differences between 1997 and 1998 were a result of: 1) a reaction of the mesofauna that migrated to the mineral soil during the extremely dry period of 1997 and 2) a consequence of the litter layer reduction that occurred in 1997, causing lower mesofauna densities. Superimposed on the micro-climatic factors, we observed the influence of the condition of the litter layer on the mesofauna densities. Depending on the physical factors, there are years of high and others with low populations. Extremely wet years could also exert an influence on the soil mesofauna and studies of long-term periods are recommended. Although there was a tendency for the Acari Non-Oribatida biomass estimated in this study to be lower than in temperate forest, the values are however higher than values recorded for many tropical forests. On the contrary, Oribatida and Collembola biomass were characterized by lower values compared to temperate forests.