Oral presentation: Milena Holmgren

Dry tropical forests are the most threatened tropical biome. Restoring them on islands is essential for supporting ecosystem functions of interconnected terrestrial and marine ecosystems. Here we identify the best strategies to stimulate dry forest recovery based on 15 years of experimentation on Bonaire. We analyzed passive and active restoration approaches conducted at different spatial and temporal scales within the same study system: 1) natural regeneration in experimental plots, 2) natural regeneration after removal of feral herbivores at landscape scales, 3) enrichment planting of seedlings under fenced remnant forest patches. We monitored tree establishment, taxonomical and functional diversity, soil hydrology and fertility. We found long-legacy effects on soils and on forest taxonomical and functional diversity. Tree seedling establishment increased when herbivores were excluded or drastically reduced. However, significant increases in sapling and tree abundance required up to 15 years of herbivore exclusion. Only one third of the dry forest tree species recruits naturally with slow shifts from conservative to acquisitive functional trait strategies as forest succession progresses without herbivores. Herbivore exclusion results in higher litter accumulation and less organic matter in runoff, but no significant differences in soil nutrients, water runoff or infiltration capacity after 9 years. Overall, our results indicate that slow recovery of degraded Caribbean dry tropical forests can be accelerated by combining herbivore removal at landscape scales with enrichment planting of rare tree species under the cover of remnant forest patches. Coupling these restoration approaches to  ENSO rainy years may facilitate dry forest recovery.