Location: Costa Rica
Organization: University of California, Santa Cruz / Las Cruces Biological Station, Organization for Tropical Studies
Large areas of agricultural land in some tropical regions are being removed from production due to complex socioeconomic forces, and rates of recovery on these lands are highly variable. Despite the fact that secondary forests play a critical role in efforts to reduce carbon emissions and conserve biodiversity, there is a lack of economically-viable and ecologically-sound strategies for restoring the extensive areas of tropical lands where natural recovery is slow. Hence, a decade ago we initiated a large-scale experiment to ask how and where to invest limited resources for restoring tropical forest. Specifically, we tested the novel idea of planting tree islands of different sizes, as a restoration strategy that is less expensive and better simulates the natural recovery process. We replicated our experiment at numerous sites with a range of surrounding forest cover so that we could (1) evaluate the importance of proximity to remnant forest on the success of restoration efforts, and (2) be able to generalize our results, given that results of restoration strategies are notoriously site-specific. Between 2004 and 2006, we set up thirteen ~1-ha experimental sites at 1000-1400 m elevation in southern Costa Rica.
Our results thus far show that plantation and island restoration strategies increase seed rain and seedling establishment to a similar degree over natural recovery plots. Second, in our system there is a critical minimum island size (~100 m2), where tree islands effectively enhance bird activity, seed rain, and tree establishment as compared to smaller islands or no planting. Third, planted islands are expanding due to both tree growth and new recruitment, and at some sites islands have coalesced. Finally, planting tree islands results in higher canopy heterogeneity and less impacts on nutrient cycling than the plantation-style planting approach. Together these results show that planting tree islands is an effective and comparatively cheaper approach to accelerate tropical forest recovery that better simulates the natural recovery process than a traditional plantation-style restoration approach.
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