The seed-to-seedling transition is limited by ground vegetation and vertebrate herbivores in a selectively logged rainforest

Due to the growing pressure to selectively log tropical forests, it is important to understand the reasons why natural regeneration can fail after logging. We addressed this with an experimental study in a selectively logged Ugandan rainforest that has failed to recover naturally. Our objective was to examine seedling emergence and performance (seedling height) and natural recruitment of indigenous tree species to better understand the factors that limit natural regeneration of forest. Seeds of 12 indigenous tree species were sown in forest gaps to examine the effect of herbaceous vegetation (manipulated with vegetation clearance), vertebrate herbivores (manipulated with vertebrate exclusion) and gap size on seedling emergence and performance, natural recruitment and seed disturbance. Seedling emergence was generally low, but showed high species-specific variation (range 0-50%). Emergence was significantly more likely to occur when vegetation was cleared and when seeds were protected from vertebrates. Seedlings also performed better when protected from vertebrates. Natural recruitment was low, limited to early successional species and enhanced by vegetation clearance. Seed disturbance was common. Our findings imply that regeneration of selectively logged forests is limited by barriers linked to herbaceous vegetation and vertebrate herbivores and granivores. However, seedling emergence and performance of some of the sown species was high, indicating that direct seeding can support reforestation efforts but that careful attention needs to be paid on species selection. Management of vegetation cover and ensuring the existence of carnivores that can control seed pests is recommended to support forest recovery on logged degraded sites.