Post-dispersal seed fate of large-seeded tropical montane trees in an agricultural landscape

Past studies of seed predation in human-dominated agricultural landscapes have commonly equated seed removal with seed predation without considering the potential for secondary dispersal by animals.  We examined variation in post-dispersal seed fate of three montane tropical forest tree species in southern Costa Rica in habitats common in tropical agricultural landscapes: forest remnants, young secondary forests, and abandoned pastures.  Our objectives were to (1) determine the rate and cause of seed mortality (predation by rodents, attack by insects and fungal pathogens, or desiccation), (2) assess the incidence of secondary dispersal by animals, and (3) compare germination success of seeds dispersed on the surface to seeds buried to mimic scatterhoarding conditions. Although causes of mortality differed among species, mortality was highest for all species in abandoned pastures (79%), intermediate in forest fragments (67%), and lowest in secondary forests (49%). Predation by rodents was highest in forest fragments (32%) compared to 16% in secondary forests and 5% in pastures. Mortality due to insects and fungal pathogens was similar for the three habitats, whereas desiccation was highest in pastures. The vast majority of secondary seed dispersal occurred in the forest fragments, and scatterhoarding occurred almost exclusively in the two larger of four forest fragments. Seed burial only affected germination in abandoned pastures, likely because it reduced desiccation. Our results suggest that the degree to which habitat is altered by human intervention affects both the causes of seed mortality and rates of secondary seed dispersal, which can influence patterns of forest regeneration.