The Extent of Biodiversity Recovery During Reforestation After Swidden Cultivation and the Impacts of Land-Use Changes on the Biodiversity of a Tropical Rainforest Region in Borneo

Abstract

Whereas many studies have addressed the effects of deforestation on biodiversity, few have focused on the recovery of diversity during reforestation. This study aimed at evaluating the recovery of, or chronosequential changes in, the biodiversity in the fallows (i.e., secondary vegetation or forests that form during the resting periods following harvest in shifting cultivation) of a tropical rainforest region in Borneo. We also aimed at determining the impacts of forest fragmentation and other land-use changes on biodiversity. We established several study plots in fallows at different stages of succession, specifically, new fallows (rested for 1–3 years), young fallows (rested for 5–13 years), and old fallows (rested for 20–60 years). We also established study plots in a continuous primary forest and fragmented primary forests, extensive rubber gardens, and other land-use types. In addition, we investigated the diversity of trees, fungi, and animals, and compared the values obtained among the different land-use types. With each progression in forest stage, the species richness, species density, and encounter rates increased for trees, fungi, army ants, and ants attending hemipterans. However, even after fallow periods of 20–60 years, the levels of diversity had not fully recovered to those recorded in primary forests. The biodiversity indices of fragmented primary forests were lower compared to those of the continuous primary forest for army ants. The biodiversity indices of extensive rubber gardens and the other land-use types were also lower compared to those of the continuous primary forest for bats. Such trends were also observed for aphyllophoraceous fungi and some insects. These results indicate the irreplaceable value of continuous primary forests for conserving biodiversity. In contrast, the species richness of small mammals and phytophagous scarabaeid beetles was similar or even higher in fragmented primary forests and the other land-use types compared to the continuous primary forest. Further studies are necessary to investigate how the characteristics of each taxonomic group (e.g., disturbance tolerance, dispersal ability, and the life history traits) are related to the different types of disturbance (intensity, spatio-temporal configurations, and the consequent changes in the environmental factors of each habitat type).