UC Santa Cruz

Tropical forest restoration has high potential to simultaneously mitigate the global climate and biodiversity crises. Though many initiatives focus on the short-term establishment of native tree cover, sustained forest recovery is contingent on many interacting ecological and social mechanisms. In my dissertation, I examined factors influencing the seedling establishment of later-successional tree species and the persistence of forest regrowth on private land in rural regions of Costa Rica.First, I conducted a seed addition experiment using eight species of later-successional tree species to compare how three restoration treatments influence seedling establishment almost two decades after initiating restoration (Chapter 1). I found that in general, seeds were able to establish as seedlings after one year in all three restoration treatments, but that treatments in which fewer trees had been planted showed greater establishment probabilities. This suggests that the availability and dispersal of seeds limits recruitment of later-successional tree species more strongly than do microsite conditions, and that direct seeding could be an effective approach for enriching existing restoration sites. Second, I experimentally tested whether vertebrates limit the recruitment of four larger-seeded later-successional tree species, a key question when restoring forest at sites where human activities have altered wildlife communities (Chapter 2). I found that seed predation by mammals and birds substantially reduced seedling establishment and to a comparable degree in plantation-style restoration plots as in remnant reference forests. Finally, to ask why private landholders clear forest regrowth and why they would consider allowing new forests to persist, I conducted semi-structured interviews at properties where tree cover loss was detected in the past five years (Chapter 3). Experiences and perspectives of landholders who recleared land suggest that policies to promote persistence of forest regrowth should expand beyond short-term payments and address concerns about land sale value, food production, and water provisioning. This work illustrates that understanding the ecological effects of restoration methods and plant-animal interactions is necessary but not sufficient to support long-term tropical forest recovery. A further challenge is ensuring that young forests can persist into the future.