Soil macro-fauna in an Acacia mangium plantation in comparison to that in a primary mixed dipterocarp forest in the lowlands of Sarawak, Malaysia

Abstract

Summary Sustainable ecosystem management of Acacia mangium plantation, the area of which is rapidly increasing in the tropics, especially in Indonesia and Malaysia, becomes more and more important. In this context, abundance, biomass and vertical distribution of soil macro-invertebrates were investigated in a mature plantation of A. mangium in Sarawak, Malaysia. In the present paper, in order to reveal the changes in soil macro-fauna caused by conversion of natural forests to A. mangium plantations, the results were compared with those from a nearby primary forest. While total abundance of soil macro-invertebrates was similar, total biomass was much larger in the plantation than in the primary forest. The prominent factor for such a large total biomass in the plantation was the high abundance of earthworms, followed by isopods and harvestmen with much smaller contributions. The common feature of the communities of these three taxa in the plantation was the absolute dominance by single species. The dominant earthworm species was of the endogeic type that was absent from the primary forest and thought to be introduced with A. mangium seedlings from outside. The isopod flushed in the plantation was a pill bug that occurred in the primary forest, too, and might have been pre-adapted to the vegetation change. The dominant harvestman in the plantation was of the life form different from that of the other species found, and was thought to be supported by the explosive increase in biomass of earthworm and/or pill bug. On the other hand, communities of termites, ants, fly larvae, click beetle larvae and other beetle larvae were depressed by the vegetation change. Thus the major consequence of the conversion of natural forest to A. mangium plantation was simplification of community structure in many taxonomic groups. The major points of the simplification in turn were the explosive increase in biomass of the soil processing earthworm and the litter processing pill bug which may accelerate the mineralization processes. The need for a careful monitoring on sustainability of soil fertility was concluded.