Slow recovery of a secondary tropical forest in Southeast Asia

Abstract

Understanding the structure and diversity of secondary tropical forests is important as they constitute an increasing proportion of tropical landscapes. However, few studies have investigated the long-term recovery of tropical forests following agricultural abandonment. We compared the physical structure and tree species composition of a 56-year-old 2-ha secondary forest plot with an adjacent 2-ha primary forest in Singapore. All trees⩾1cm in diameter were surveyed. We found that after 56 years of recovery, the secondary forest remains floristically and structurally distinct from the adjacent primary forest. The secondary forest plot had 30% of the stem density, 58% of basal area, 26% of species richness and 59% of the Shannon diversity as compared to the primary forest plot. Nonmetric multidimensional scaling analysis and partial Mantel tests showed that the floristic composition of the two plots was distinct, even after accounting for the underlying spatial gradient in composition. Nevertheless, some shade tolerant species such as Streblus elongatus and Calophyllum spp. were thriving in the secondary forest. Our findings suggest several possible mechanisms for the slow recovery of the secondary forest, including strong dispersal limitation and the presence of long-lived pioneer species.