Seed rain in cocoa agroforests is induced by effects of forest loss on frugivorous birds and management intensity

Abstract

Tropical forests have been intensively degraded and deforested for different anthropogenic uses, mostly associated to agricultural expansion due to increasing human demands. Therefore, an emerging number of studies has advocated on the benefits of land-sharing strategies such as agroforestry systems which conciliate biodiversity conservation with production. Yet features at both landscape and local scales could affect ecological processes and productivity within agroforests. Here, we used structural equation models to investigate the direct and indirect effects of landscape forest cover, animal seed dispersers and local vegetation variables on the seed rain structure of cocoa (Theobroma cacao) agroforests of the Brazilian Atlantic forest. We sampled seed rain for 12 consecutive months, performed bird and bat surveys and measured local structure variables related to management intensification (i.e., lower abundance and richness of adult trees and lower canopy shading indicating farm intensification) in 15 farms embedded within landscapes showing varying forest cover amount (2.3–74.9 %). Our results indicate that total and animal-dispersed seed richness in cocoa agroforests increased in more forested landscapes induced by the frugivorous bird richness, whereas the abundance of total and animal-dispersed seeds was greater in more shaded farms. Contrary to expectations, the abundance of total and animal-dispersed trees negatively influenced the richness of frugivorous birds, thus indirectly affecting the richness of total and animal-dispersed seeds. Finally, we observed a weak similarity among the composition of arrived seeds and adult trees of animal-dispersed species recorded in the same sampling sites, suggesting that several seeds were actively dispersed from other localities. Our results therefore demonstrate that landscape forest amount and local management intensification play key roles in determining the seed diversity reaching cocoa agroforestry farms. We emphasize the importance of retaining native vegetation cover around the cocoa agroforestry, by either preserving the existing forest remnants or promoting restoration programs within deforested landscapes, in addition to locally ensure tree shading to boost seed arrival and enhance ecosystem functionality.