PS 2-31 - Carbon sequestration performance analysis; Lessons from a community-led reforestation project in the Neotropics.

Background/Question/Methods

The ability of trees to sequester carbon as they grow has pushed reforestation to the forefront of the global agenda on climate change mitigation. International commitments, such as the Bonn challenge, aim to increase global reforestation rates seven-fold in the next decade. This enormous upscaling is an opportunity to push forward ecologically and socially beneficial solutions by planting diverse species and involving Indigenous Peoples and Local Communities (IPLCs). However, projects that aim to maximise carbon, ecological and social benefits involve a high level of uncertainty since they are complex and understudied. In practice, most reforestation initiatives are commercial monocultures.
Participatory action research can bolster the adoption of more holistic practices by building theory that is directly applicable. Our research offers lessons from a ten-year-old community-led reforestation project in Panama built on participatory action research principles. We compare growth and survival of eleven native timber and fruit species in monocultures, mixtures, agroforestry, and enrichment planting systems using statistical analyses (Generalized Linear Mixed Models). We use the Loreau & Hector (2001) methodology to measure the biodiversity effect and redundancy analyses to quantify the importance of social, environmental and design characteristics on the project.

Results/Conclusions

We observed a large biodiversity effect with timber mixtures storing an average 175tCO2/ha; 45% more carbon per hectare than timber monocultures. 80% of this difference was attributed to complementarity effect and 20% to selection effects with the species Terminalia Amazonia storing the most carbon (p< 0.001). Agroforestry and enrichment planting stored only ~50tCO2/ha each. This can be explained in part by the planting design with a lower tree density. In return, for agroforestry, the reduced competition led to larger individual trees (p< 0.05). Moreover, three fruit species sequestered a comparable amount of carbon as timber species: Inga punctata, Anacardium Occidentale and Mangifera indica.

The difference in performance between plots was explained by design (28%), maintenance (20%) and environmental characteristics (4%). Notably, fire spillover from slash-and-burn agriculture damaged 8 of the 14 plots and destroyed two entirely. Meanwhile, natural regrowth from enrichment planting and post-fire proved to be an important carbon sink accounting for 31% of the project’s total carbon.

Natural regrowth brought more biodiversity of trees with no planting costs, fruit species increased food security and timber species optimized carbon sequestration. Our study highlights trade-offs, threats, and promising species to reduce uncertainty around community-led reforestation projects in the neotropics.