Bracken fern facilitates tree seedling recruitment in tropical fire-degraded habitats

Tropical forest regeneration is hindered by human-induced fires. After deforestation by fires, Pteridium spp. (bracken fern) often colonizes and dominates the vegetation for long time periods, presumably inhibiting the succession. Tree species from mature forests are rare in the degraded areas, potentially due to the lack of seed dispersal and unfavourable abiotic conditions. Here, we experimentally assess the effect of bracken presence, in terms of litter and shade, on seedling recruitment of three native, shade-tolerant tree species in the tropical mountains of Bolivia. In a spatially blocked design at eight sites, we compared seedling recruitment, survival and growth three months and one year after sowing between experimental litter and vegetation treatments and among habitat types (forest interior, degraded habitats close and far from the edge) and species (Clusia sphaerocarpa, Clusia lechleri and Clusia trochiformis). We found that species differed in their recruitment success and habitat preferences, but responded similarly to experimental treatments. Litter removal increased temperature and reduced humidity on the ground and vegetation removal increased canopy openness. Seedling recruitment was consistently reduced by litter and vegetation removal, and their interaction had a deleterious negative effect. Seedling survival and growth were also reduced by litter removal. Our results highlight the overlooked facilitative effects of bracken by ameliorating harsh abiotic conditions and increasing the probability of Clusia seedling recruitment and potentially other shade-tolerant tree species in degraded habitats. To enhance forest regeneration in fire-degraded areas, we recommend spreading seeds of shade-tolerant tree species into the bracken vegetation. This method is less costly and might be more efficient than previous methods that involved repeated bracken removal. Recruitment of late-successional species in the bracken vegetation is likely to promote the restoration of tropical forest; however, long-term studies are needed to test the success of such efforts.