Session: Can Nucleation Bridge to Desirable Alternative Stable States? Theory and Applications
Scaling up spatially-patterned planting methods to restore tropical forest
Wednesday, August 4, 2021
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Karen D. Holl, Environmental Studies, University of California, Santa Cruz, Santa Cruz, CA, Pedro H. S. Brancalion, Department of Forest Sciences, University of São Paulo, Piracicaba, Brazil and Rakan A. Zahawi, Charles Darwin Foundation, Ecuador; Lyon Arboretum, University of Hawai’i at Mānoa, Honolulu, HI
Karen D. Holl
Environmental Studies, University of California, Santa Cruz Santa Cruz, CA, USA
Background/Question/Methods Spatially-patterned planting methods, such as applied nucleation or planting strips of trees, are a promising method to accelerate forest succession and create more heterogeneous habitat than standard, plantation-style tree planting approaches. Spatially-patterned planting methods also require less resources to plant and maintain and therefore hold potential as a practical method to scale up restoration efforts to meet the many ambitious international forest restoration commitments. But, few past studies have compared spatially-patterned planting to other restoration approaches over a sufficient spatial and temporal scale to inform on-the-ground restoration. We review key social and ecological lessons learned from our 17-yr restoration study, replicated at 12 sites in southern Costa Rica, that compares applied nucleation to natural regeneration and mixed-species tree plantations. We also discuss more recent experiments in the Atlantic forest of Brazil that test applied nucleation and strip planting. We are in the process of summarizing the practical implications of this research for conservation organizations in order to apply these methods to large-scale restoration projects. Results/Conclusions Results indicate that applied nucleation and plantation restoration strategies are similarly effective in enhancing the recovery of most floral and faunal groups, vegetation structure, and ecosystem functions, as compared to natural regeneration. Nonetheless, after 17 years of recovery the species composition in restoration treatments still differs substantially from reference forest. Larger tree nuclei more effectively attract faunal seed-dispersers and shade out grasses. The applied nucleation strategy is cheaper than mixed-species tree plantations, but there may be social obstacles to implementing this technique in agricultural landscapes, such as perceptions that the land is not being used productively. Initial results from the Brazilian study suggest that strip planting may have similar benefits to applied nucleation in facilitating recovery and creating habitat heterogeneity. And, the strip planting design is more practical and cheaper to implement using machinery. Furthermore, interplanting strips of native species with fast growing Eucalypts which are logged after 5-7 years can achieve similar ecological outcomes and help offset restoration costs. Our collaborations with Conservation International, the Atlantic Forest Restoration Pact, and the Suzano company, who are all applying these spatially-patterned planting methods across restoration projects of tens to hundreds of hectares, suggest their promise for scaling up tropical forest restoration.