Chronosequential changes in species richness of forest-edge-dwelling butterflies during forest restoration after swidden cultivation in a humid tropical rainforest region in Borneo

Abstract

In contrast to the large number of studies addressing the effects of deforestation on insect diversity, few studies have focused on the recovery of diversity during forest restoration. In this study, we investigated the recovery, or chronosequential change, of butterfly species richness during forest restoration after cessation of swidden cultivation in a humid tropical rainforest region in Borneo. Through conducting censuses on butterflies at 21 study plots, placed at open habitats adjoining edges of forest stands that differed in elapsed years after cessation (<3, 5–13, and 20–60 year-old fallows, and isolated and large-area primary forests), we obtained presence or absence data on 132 butterfly species. The cumulative number of observed species was significantly higher at two types of primary forests than at three types of fallows; significantly higher at two older fallows than the youngest fallows; and not significantly different between the two older fallows. The species number in the older fallows was less than half that of either type of primary forest. The numbers of species at the oldest fallows and isolated primary forests significantly decreased with distance from the large-area primary forests, and the majority of butterflies observed in the fallows were also observed in the primary forests. These results suggest that although the species richness of forest-edge-dwelling butterflies recovers in the initial 20 years of forest restoration, the recovery pace decreases thereafter and depends on the presence of large-area primary forest in the vicinity. It is suggested that forest fragmentation also decreases butterfly diversity.