Proximity and abundance of mother trees affects recruitment patterns in a long-term tropical forest restoration study

Remnant trees and forest fragments in agricultural landscapes can be important sources of propagules to facilitate forest recovery. However, many studies simply quantify forest cover in the surrounding landscape as a percentage, with little attention given to species composition, and subsequently fail to detect an effect on recruitment patterns. We assessed the relative importance of the spatial distribution and life-history traits of 77 tree species on recruitment patterns at a landscape scale in a well-replicated long-term restoration study in southern Costa Rica. We censused and mapped potential mother trees in a 100-m buffer surrounding eight replicate restoration plots and quantified respective tree recruits within each plot. We assessed how mother tree abundance, species life-history characteristics (seed size, dispersal mode), tree size (DBH, height) and distance to restoration plot affected recruitment at coarse (plot: 50 x 50 m) and fine (quadrat: 3 x 3 m) spatial scales. The presence of a mother tree within 100 m of a restoration plot resulted in a 10-fold increase in potential mean recruitment. Mother tree abundance was also an important driver of recruit density, and particularly so for large-seeded (>= 5 mm) zoochorous species with a fivefold increase in recruit density across the observed mother tree abundance range. An interaction between mother tree abundance and proximity demonstrated that the effect of mother tree abundance on recruit density was important but waned with increasing distance from restoration plots. At the fine spatial scale, proximity was uniformly important; height and DBH of the closest potential mother tree also affected recruit abundance but responses differed by seed size. Results highlight the importance of remnant vegetation composition to the recovery of adjacent degraded habitats, underscoring the outsized role nearby remnant forest and isolated trees can play for the persistence of localized biodiversity.