LB 9-91 - Seed limitations in a tropical forest hotspot

Seeds and seedlings represent the earliest and most critical stages of plant life cycle, driving plant recruitment and forest regeneration patterns. Recruitment limitation occurs when seeds do not reach the available places in the forest (i.e., seed limitation, which includes source and dispersal limitations), or do not find adequate conditions for seedling emergence and growth (i.e., establishment limitation). Although recruitment limitation affects the dynamics and composition of tropical forest communities, seed limitation and its components have seldomly been accessed in the fragmented landscape of the Brazilian Atlantic Forest, a biodiversity hotspot. Hence, our study aims to investigate the drivers of seed limitation (seed, source and dispersal limitations) related to vegetation type (native forest, reforestation, urban fragments, isolated trees, open systems) and regeneration traits (dispersal mode, seed size and successional status of species) through remnants of the Atlantic Forest, from South to Northeast Brazil. This is a collaborative study that counts with primary data provided by the authors across 51 study sites. Based on the number of traps that received seeds, the total number of seeds, and the total number of traps in each study, we calculated seed, source and dispersal limitations and tested these parameters as a function of vegetation type and regeneration traits using GLMM models. The regeneration traits were obtained from the TreeCo project (Neotropical Tree Communities database). Our results show that vegetation type has a significant effect on seed limitations: isolated trees seem to display lower seed, source and dispersal limitation values compared to forest formations (P < 0.01), but probably for receiving seeds from the isolated tree species itself. Regarding seed size, larger seeds tend to present higher seed and source limitations than the small-seeded species (P < 0.001). The ecological/successional status of species also helps to explain the patterns of seed and source limitation, including a significant interaction with seed size for the source limitation (P=0.041). Contrary to expectations, however, dispersal mode did not show a significant relationship with seed limitations in our preliminary analysis. Additional analyzes are needed to understand the role of functional traits in limiting seed dispersal and recruitment, and we must consider the strong correlation between seed size, dispersal mode and successional status in tropical forests. In mosaics of fragmented environments and open areas, early successional species can be less susceptible to the effects of isolation, thus helping to explain the decrease in seed/source limitations that we have found for the isolated trees.