Tree species diversity relative to human land uses in tropical rain forest margins in Central Sulawesi

Abstract

The large-scale exploitation and conversion of tropical forests causes growing concern about the continued existence of the rich biodiversity of these forests. In the framework of the interdisciplinary STORMA project in Lore Lindu National Park area in Central Sulawesi, we studied tree diversity in six different land use types in the margins of submontane rain forest: undisturbed forest, forest with rattan extraction, selectively logged forest, cacao forest gardens, cacao plantations with mixed canopy of planted trees, and cacao plantations with a monospecific canopy. By analyzing such a finely subdivided use gradient it was attempted to answer the question how human usage and biodiversity conservation in the study area may be reconciled. Tree species (dbh > 10 cm) were sampled in 24 plots of 0.25 ha in all six land use types (4 replicates each). In total, 251 tree species (143 genera, 59 families) were recorded. Number of tree species per 0.25 ha was 51–63 in primary forest and gradually decreased towards the studied cacao systems. However, when native and cultivated tree species were considered separately, significant differences were detected among plantation types in terms of tree diversity. Tree endemism in forest plots totalled ca. 15% and was in good accordance with endemism in woody plants of Sulawesi. The number of endemic species was strongly reduced in cacao systems, although percentage endemism did not decline significantly in cacao forest gardens. Roughly one third of tree species in the forest plots were of economic importance as commercial timber trees; timber diversity was little affected by moderate human use of the forest but was significantly reduced in cacao forest gardens and dropped to near zero in other plantation types. The mean basal area of 57 m2 (36–80 m2) per ha in natural forest was lower than the previously recorded value from the study area but is still almost double as high as the mean value typical for tropical lowland forests in Southeast Asia.