Reproductive success of a tropical tree, Shorea laxa, in a pulau (forest reserve) managed by a local community in Borneo.

摘要

For local communities of Sarawak, Malaysia, pulaus (forest reserves) are important components of agriculture and forestry systems, e.g., as seed orchards. However, pulaus are often fragmented, which may affect tree reproductive and regeneration processes and cause low seed production or seedling survival. Here, we investigated whether the pulau system affects the reproductive success of a tropical tree, Shorea laxa (Dipterocarpaceae). First, we compared survivorship during the flower-to-seedling stages, seed fate and seedling mortality between a pulau and a primary forest. Next, we evaluated the neighborhood aggregation effect, i.e., local density effect, on the reproductive process. Finally, through microsatellite analysis using seed arrays, we examined the pollination process including the selfing rate, genetic diversity and pollen dispersal distances. We found no clear differences in tree survivorship during the flower-to-seedling stages between the two sites. However, predation by vertebrates was lower in the pulau, possibly because of a lower density of seed-predating vertebrates. Neighborhood aggregation was negatively correlated with seed maturation and seed survival in the pulau, similar to the primary forest. However, the scale of neighborhood aggregation differed between the two sites, suggesting a change in the scale of plant-animal interactions. Although pollen dispersal was limited within the pulau, a low selfing rate and high genetic diversity of the seed array indicated effective pollination. In this study, we did not find a strong negative effect of the pulau or of forest fragmentation on the reproduction and regeneration of S. laxa. The pulau investigated in this study was shown to provide genetically rich seeds. We also discuss the importance of the pulau system from a conservation perspective.