The seedling community of tropical rain forest edges and its interaction with herbivores and pathogens

Edge effects alter biotic interactions and forest regeneration. We investigated whether edge creation affected the seedling community and its interactions with herbivores and leaf-fungal pathogens. In forest edges and interior sites in Chiapas Mexico, we counted all woody seedlings and species (10-100 cm tall) present in 1-m(2) plots, measured their size (height and leaf number), and examined them for the occurrence of herbivory and pathogen damage. We investigated relationships between levels of damage and size, species richness and density. Species composition and biotic damage varied greatly among sites and habitats (edge vs interior). Late-successional species dominated the community, but richness was lower in interior sites and species similarity was greater among edges than among interiors. Nearly all species (95%) present at edges and interiors showed herbivory damage, whereas 76 percent of the species in edge plots and 68 percent in interior plots showed pathogen damage. Although leaf area damaged by herbivores was similar between habitats (average 9.2%), pathogen damage was three times greater in edge plots (1.85%) than in interior plots (0.57%). Size was positively related to biotic damage at both habitats. Relationships between herbivory and pathogen damage and between pathogen damage and leaf number were significant only for edges. Biotic damage was not related to density or species richness. Overall, plant community structure was similar between habitats, but biotic damage was enhanced at edges. Thus, disease spread at edges may arise as a threat to tropical rain forest vegetation.