Frugivore communities and seed rain in regenerating pastures in Costa Rica

Background/Question/Methods

Early secondary succession on degraded, tropical pastures is limited in part by a lack of seed dispersal. Because most Neotropical tree seeds are dispersed by animals, a primary challenge for ecological restoration is to create conditions that attract vertebrate frugivores into degraded environments with few opportunities for food or cover. We used a novel restoration experiment replicated at 13 sites across an agricultural landscape (~100 km²) in southern Costa Rica to study the effects of local restoration interventions, landscape context, and their interaction on the abundance, diversity, and composition of birds, bats, and seed rain 3-8 years after site establishment. Restoration sites were established in 2004-2006, and each site contains three 50 × 50 m plots randomly assigned one of three treatments: not planted (control), 86 seedlings of four species planted in patches (two each of 4 × 4, 8 × 8, 12 × 12 m; nucleation treatment), and 313 trees of the same species planted in rows throughout (plantation). Tree cover in landscapes surrounding restoration sites varies from 11-88% within a 500-m radius. We evaluated how local restoration treatments and landscape context interact to attract vertebrate frugivores into degraded areas.

Results/Conclusions

Local restoration and landscape context interacted to predict bird community composition. Frugivore abundance was greatest in plantations regardless of landscape context - possibly a result of niche complementarity between frugivore communities in forested and agricultural landscapes. In contrast to birds, bat communities were less strongly related to local restoration strategy and landscape context – consistent with some other nocturnal animals. Seed rain abundance in restoration sites was dominated by wind-dispersed individuals (Asteraceae, Heliocarpus), but most species were animal-dispersed, and most animal-dispersed seeds were small (<1 cm diameter; Solanum, Cecropia, Miconia, Piper). Dispersal rates for small-seeded species were similar across local restoration treatments, but compositional similarity to mature forest and dispersal events of larger seeds (>1 cm diameter) were greater in plantations than in nucleation treatments or controls. Our results suggest that a complete lack of vertebrate frugivores is unlikely in our study system, even in the most degraded sites. Regenerating pastures with few vertebrate frugivores are likely to have reduced animal-dispersed seed rain - particularly for large-seeded tree species. Given projections for large-scale forest recovery in post-agricultural lands in Latin America, it seems likely that future forests will initially be dominated by wind-dispersed and small animal-dispersed seeds.