Habitat loss and fragmentation are leading threats to biodiversity. However, interpreting fragmentation effects remains challenging because impacts can be numerous and confounded in observational systems. Here, we evaluate how fragmentation influences seed dispersal, a process commonly thought to be impacted by fragmentation, with ramifications for the spread and persistence of plant populations. We do so within a replicated, large-scale fragmentation experiment that independently manipulates three aspects of fragmentation – patch connectivity (through corridors), patch shape (edge:area ratio), and proximity to edge. Across five transplanted herbaceous plant species, we marked seeds of 1083 individual plants with fluorescent paint and re-found these seeds to a distance of 5m from the parent plant after dispersal. We then constructed and compared dispersal kernels across our landscape treatments of connectivity, edge:area ratio, and edge distance. We predicted greater dispersal distances in connected and high edge:area patches and far from edges based on known wind dynamics in our system of open savanna habitat patches surrounded by plantation forest. In our system, wind speeds and uplift are greatest in connected patches, and intermediate and low in patches with high and low edge:area ratios, respectively. Additionally, uplift is greater near the center of patches. We also predicted that landscape-level differences in dispersal would be most pronounced for two wind-dispersed species (those with morphological adaptations, e.g., a pappus) and less pronounced for three species lacking such adaptations.
Results/Conclusions
Habitat fragmentation affected seed dispersal as we predicted, but largely only for wind-dispersed species. Wind-dispersed species travelled greater distances in connected vs. unconnected patches and in patches with higher edge-to-area ratios. Conversely, for species lacking morphological structures for wind, dispersal distances were greater in unconnected patches and those with low edge-to-area ratios. Dispersal distances were greater far from edges for three species and near to edges for two species. Together, our results illustrate how fragmentation affects seed dispersal in several ways related to wind dynamics – by severing connectivity, altering patch shape, and creating edge effects. Dynamics between these habitat factors, species dispersal mode, and abiotic factors such as wind, are important for understanding how species spread and colonize new territory. Our findings provide further support for the use of corridors in restoration and conservation, and have implications for the design of reserves and habitat restoration projects.