The maintenance of seedling diversity of animal-dispersed tree species is fundamental for the structure and function of forest patches in fragmented tropical rainforests. Nonetheless, the effects of landscape structure at different spatial scales on α- and β-diversity of tree seedling communities are recently explored. Using a multi-scale approach, we assessed the relative effect of landscape composition and configuration on α- and β-diversity of animal-dispersed seedlings within 16 forest patches in the Lacandona rainforest, Mexico. We assessed these effects at 13 spatial scales (from 300 to 1500 m radius, at 100 m intervals) for three metrics of effective number of species considering α- and β-diversity. We found that α-diversity was largely affected by landscape composition and β-diversity by landscape configuration. On the one hand, the amount of secondary forest influenced α-diversity. Additionally, species richness increased in landscapes with highly aggregated forest patches. On the other hand, β-diversity was affected positively by forest fragmentation and negatively by the edge contrast of forest patches with the surrounding matrix. Our findings indicate that landscape configuration is a strong driver of seedling diversity in highly deforested rainforests.

We selected 16 old-growth forest patches, ranging from 1 ha to 63 ha. Patches were sampled by 1-ha blocks placed at the center of each forest patch. Each block contained ten 1-m² plots randomly arranged in groups of two or three plots along five equidistant transects (20 m apart). For 1-ha forest patches, we never positioned plots at the edge in order to have a 20-m buffer zone of vegetation that protect them from edge effects as much as possible. Within each 1-m² plot we counted and identified all tree seedlings (10-100 cm height) to the lowest possible taxonomic level with the help of a local parataxonomist and field guides. When field identification was not possible, we took samples for identification at herbariums (MEXU, ECO-SC-H). We determined the dispersal syndrome of each species, based on their fruits and seed morphology. This study did not involve the extraction or damage of endangered species. We based our analyses on animal-dispersed tree species only because they comprise up to 90% of the seed rain in rainforests. Plant nomenclature followed the Missouri Botanical Garden database Tropicos.

Values refer to abundance per 1 m-2 plot. The first column indicates the ID of the plot.