Persistent effects of landscape connectivity on recruitment dynamics in secondary forests

Large scale reforestation is promoted as an important strategy to mitigate climate change and biodiversity loss. A persistent challenge for efforts to restore ecosystems at scale is how to accelerate ecological processes, particularly natural regeneration. Yet, despite being recognized as an important barrier to the recovery of diverse plant communities in agricultural landscapes, the impacts of dispersal limitation on natural regeneration in secondary forests – and especially how this changes as these forests grow older – is still poorly studied at local and landscape scales. Here, we evaluate the multi-scale impacts of proximity to a connected network of forest fragments on recruitment in 1–40-year-old secondary forest. We used eight years of annual census data from 45 sites with paired plots, one directly adjoining a streamside forest fragment and the other further uphill, and a null model approach to test the effects of basal area and proximity to streamside forest fragments. In general, we found that proximity to streamside forest fragments enhanced multiple aspects of recruitment across spatial scales, including species diversity and the proportion of rarer and less-widely distributed species among the recruits. Unexpectedly, this effect did not weaken over time, despite a fast increase in stand basal area, canopy complexity and diversity. This suggests that successional changes in forest structure may not be sufficient to attract the animals that disperse rarer tree species. Our results provide empirical evidence to guide restoration initiatives in agricultural landscapes in tropical regions, principally prioritizing the restoration of forest corridor networks along streams, while also highlighting the knowledge gap about restoring animal dispersers in secondary forests.