Background/Question/Methods Fragmentation of tropical forests is a major cause of global biodiversity loss, however the effects of forest fragmentation on the biodiversity and species composition of neotropical forest regeneration are poorly understood. We hypothesized that forest fragmentation negatively affects the diversity of regenerating neotropical forests and alters species composition of tree and shrub regeneration and tested these hypotheses at the Biological Dynamics of Forest Fragments Project site, located in the Brazilian Amazon. In 120, 10 m² experimental plots we compared tree and shrub seedling species richness and composition in continuous forest controls to forest fragments of different sizes  (1, 10, and 100 ha) and also at different distances from forest fragment edges to determine whether area and edge effects respectively affect forest regeneration dynamics. To determine the importance of various factors hypothesized to affect the species diversity and community composition of forest regeneration, we measured abiotic (light, soil moisture, temperature, humidity, soil nutrients) and biotic (seed rain, seed predation, herbivory) factors at each of our experimental plots.
Results/Conclusions Overall, we recorded 11,596 tree, shrub and liana seedlings of 858 species regenerating in our 120, 10 m² subplots; of these 7,851 individuals of 673 species were trees and shrubs, the remaining individuals were lianas. Most of these tree and shrub species were rare, with only 25.7% of the species having more than 50 individuals. The species richness of tree and shrub seedlings was significantly lower (ANOVA: F _3,5 = 11.6; P = 0.011) and species community composition significantly different (RDA: F _3,5 = 1.53; P = 0.011) in forest fragments compared to continuous forest. Species richness was significantly lower (ANOVA: F _5,23 = 13.0; P = 0.0002) closer to forest fragment edges, especially less than 10 m from the edge. We discuss which species characteristics are most vulnerable to forest fragmentation, and the relative contribution of abiotic and biotic factors driving these biodiversity losses and species compositional changes in forest fragments. We conclude that both area and edge effects significantly alter species composition and lower biodiversity of forest regeneration in forest fragments in the Brazilian Amazon.