Edaphic characteristics and environmental impact of rubber tree plantations on soil mite (Acari) communities

Abstract

The objective of the investigation was to determine the response of different taxa of mites across the land use types and demonstrate that soil mites could be used as an indicator of environmental change after the conversion of secondary forests into rubber plantations. The sampling was performed during the dry season on 12 sampling areas, consisting of four land use types: secondary forests, 7-year-old rubber plantations, 12-year-old rubber plantations, and 25-year-old rubber plantations, with three replications of each treatment. Soil cores were sampled along a 40 m transect with a steel corer. The soil mites were extracted using modified Berlese-Tullgren funnels during a 10 day period. Soil physico-chemical parameters were measured on each sampling area. The conversion of secondary forests into rubber plantations was characterized by a modification of the mean values of mite density (+103 and +262%), species richness (-11 and +32%), water content (-41 and -5%), bulk density (+6 and -3%) and soil organic carbon (-73 and -59%) respectively, after 7 and 25 years of conversion. The density of mites, species richness and soil water content increased with the aging of the rubber plantations, demonstrating an improvement in soil ecological quality and environmental conditions. These results are confirmed by the values of the Maturity Index of Gamasid mites, which increased with the increasing age of rubber plantations. In other words, the severity of environmental impact decreased with the aging of the rubber plantations and was ranked as follows: 25-year-old rubber plantations < secondary forest < 12-year-old rubber plantations < 7-year-old rubber plantations. The Maturity Indexes estimated that 25-year-old rubber plantations (0.84) and in secondary forests (0.74) are relatively similar and characterize stable habitats, which are potentially dominated by Gamasid species with K selection.