Relationships between tree-community composition and regeneration potential of Shorea trees in logged-over tropical rain forests

Abstract

ABSTRACT Logged-over forests are widespread in SE Asia, and these forests vary greatly in tree-community composition ranging from a near pristine to a greatly modified forest due to repeated high-impact logging. It is a critical concern in terms of forest management and conservation whether modified forests can recover to their original states. However, greatly modified forests may lose the resilience due to the lack of next-generation seedlings. We examined the regeneration potential of Shorea, a dominant genus in pristine forests, in various forests ranging from pristine to degraded forests, and investigated the relationship between the tree-community composition in canopy layer and the regeneration potential in north Borneo. In non-metric multidimensional scaling (nMDS) analysis based on the tree-community composition at genus level, 31 study plots were sorted in the order from pristine to degraded forests along the axis-1 with decreasing the axis-1 scores, and this score was used as a metric of forest intactness. Size distribution of Shorea trees combining all congeneric species showed an inverse-J shape in most plots excluding some degraded forests. The skewness of size distribution was high in pristine forests but remarkably decreased in degraded forests. The skewness reflected the abundance of seedlings in the population of Shorea trees, and it was an important metric indicating regeneration potential. The number of seedlings also decreased abruptly with decreasing forest intactness along the nMDS axis-1. The reduction in these two metrics suggests that regeneration potential is abruptly lost when the forest intactness in terms of tree-community composition is decreasing.