Forest structure and connectivity drive the functional recovery of seed rain

Tropical forest recovery is triggered by seed dispersal provided by animal frugivores. Plant and animal traits shape the interactions between plants and frugivores, ultimately determining the functional diversity of seed rain. However, it remains poorly understood how the functional diversity and composition of plant–frugivore interactions and seed rain are affected by processes at both local and landscape scales. We investigated how local forest structure and landscape-scale forest connectivity shape the functional recovery of seed rain mediated by plant–frugivore interactions. At 24 recovering forest and 8 old-growth forest plots, we measured forest structure and connectivity, recorded plant–frugivore interactions and quantified seed rain in a total of 384 seed traps. Forest structure was quantified from vegetation heterogeneity, above-ground biomass and tree height, and forest connectivity from surrounding forest cover and the distance to the closest forest. Using plant and frugivore traits, we quantified the functional recovery of plant–frugivore interactions and seed rain and applied structural equation models to test the direct and indirect effects of forest structure and connectivity on the functional diversity and composition of seeds. Forest structure primarily influenced seed rain functional diversity mediated by local plant–frugivore interactions. In addition, forest connectivity was the main driver of the functional composition of seed rain. Large seeds and seeds of late-successional species were found more often in recovering forests with high connectivity, both through direct and indirect effects via plant–frugivore interactions. These patterns suggest two complementary mechanisms of forest recovery. Structurally complex forests support diverse plant and animal communities that foster a functionally diverse seed rain. Forest connectivity, in addition, promotes animal movement across the landscape, facilitating the dispersal of seeds from old-growth forests into recovering forests. Synthesis. Local forest structure and landscape-scale connectivity shape distinct but complementary aspects of the functional recovery of seed rain. These findings highlight that tropical forest restoration requires considering both local and landscape-scale processes to ensure the recovery of functionally diverse tropical forests.