A COMPARISON OF ABOVEGROUND CARBON STORAGE IN AGROFORESTRY SYSTEMS AND IN SECONDARY FOREST IN COSTA RICA

Land use change, particularly through deforestation, is the second largest contributor to greenhouse gas emissions globally. Tropical forests are of particular interest when developing climate change mitigation strategies as they sequester more carbon in living biomass than any other terrestrial ecosystem. To reduce emissions, international and national programs that promote forest preservation, reforestation, and agroforestry are being introduced. Internationally, the Kyoto Protocol promotes reforestation as a clean development mechanism and Reduction in Emissions from Deforestation and Degradation is working to provide funds for preserving existing forests. Some countries, including Costa Rica, have initiated Payment for Environmental Services (PES) programs, which compensate landholders for forest preservation, reforestation, and new agroforestry. This study quantified carbon stored in the aboveground living biomass of a 40-yr old tropical secondary premontane moist forest (n=3 plots) and of organic and conventional agroforestry coffee farms (n=7 each) in the Central Valley of Costa Rica. Diameter at breast height (DBH) and species identity were recorded for all trees with DBH ≥ 5cm within sub-plots totaling 0.2 ha for each location. Allometric equations were used to calculate aboveground carbon. We found that the forest contained significantly more carbon in aboveground tree biomass than did the organic and conventional coffee farms with median values of 144.1 tC/ha, 43.9 tC/ha, and 18.1 tC/ha, respectively. When carbon content of coffee plants was added, organic coffee farms sequestered more carbon than conventional farms, though the difference was not statistically significant, with median values of 47.4 tC/ha and 25.4 tC/ha, respectively. Additionally, organic farms had significantly more trees than did conventional farms, with medians of 498 and 262 trees/ha, respectively. Quantifying carbon stored in the living biomass of different land use types, especially in areas that have been changed from forest to agriculture, is critical in determining current carbon stocks and storage potential. This research can be used to justify PES programs and other greenhouse gas mitigation strategies that promote reforestation, forest preservation, and new and pre-existing agroforestry.