Multiple stages of tree seedling recruitment are altered in tropical forests degraded by selective logging

Abstract

Tropical forest degradation is a global environmental issue. In degraded forests,seedling recruitment of canopy trees is vital for forest regeneration and recovery. Weinvestigated how selective logging, a pervasive driver of tropical forest degradation,impacts canopy tree seedling recruitment, focusing on an endemic dipterocarpDryobalanops lanceolata in Sabah, Borneo. During a mast-fruiting event in intensivelylogged and nearby unlogged forest, we examined four stages of the seedling recruitment process: seed production, seed predation, and negative density-dependentgermination and seedling survival. Our results suggest that each stage of the seedlingrecruitment process is altered in logged forest. The seed crop of D. lanceolata trees inlogged forest was one-third smaller than that produced by trees in unlogged forest.The functional role of vertebrates in seed predation increased in logged forest whilethat of non-vertebrates declined. Seeds in logged forest were less likely to germinatethan those in unlogged forest. Germination increased with local-scale conspecificseed density in unlogged forest, but seedling survival tended to decline. However,both germination and seedling survival increased with local-scale conspecific seeddensity in logged forest. Notably, seed crop size, germination, and seedling survivaltended to increase for larger trees in both unlogged and logged forests, suggestingthat sustainable timber extraction and silvicultural practices designed to minimizedamage to the residual stand are important to prevent seedling recruitment failure.Overall, these impacts sustained by several aspects of seedling recruitment in a mastfruiting year suggest that intensive selective logging may affect long-term populationdynamics of D. lanceolata. It is necessary to establish if other dipterocarp species,many of which are threatened by the timber trade, are similarly affected in tropicalforests degraded by intensive selective logging.