Carbon stock and tree diversity of dry-zone homegardens in Southern Sri Lanka

Conference poster, 2014

Traditional land-use systems such as tropical homegardens hold a large potential for climate change mitigation and adaptation due to their multi-functional role in providing income and ecosystem services while decreasing pressure on natural forests. Although, the importance and recognition of homegardens has been highlighted for their large potential in carbon sequestration, tree diversity and functioning there is still lack of quantitative data on homegardens and their contribution to climate change mitigation. In this study, tree diversity and above-ground biomass carbon of woody species was estimated on a local level around the village of Beralihela in the dry south-eastern part of Sri Lanka. A total of 45 homegardens were sampled on size, floristic composition of trees, girth at breast height (GBH) and height of trees. In total, 4278 trees were sampled and 82 different tree species were recorded. The Shannon Wiener index used to evaluate biodiversity ranged from 0.76–3.01 with a mean value of 2.05. Using allometric models, we find a mean above ground biomass carbon stock of 13 Mg C ha-1 with a large range among homegardens (1–56 Mg C ha-1, n=45) due to a variation of tree diversity, species and composition between individual homegardens. Per unit area basis, above ground carbon stock was higher in small homegardens (26 Mg C ha-1) than medium (9 Mg C ha-1) and large (7 Mg C ha-1) homegardens due to a higher tree density. The results of this study contribute to closing the knowledge gap of the less studied dry-zone homegarden agroforestry systems and their function in storing carbon and provide multi-functional benefits to its users. The results are also useful for the national process of whether homegardens should directly or indirectly be considered to be included as an activity within Sri Lanka’s newly commenced UN-REDD National Programme. This study shows the potential of using tropical homegardens for future land-use planning and multiple benefits including carbon sequestration potential, particularly in terms of land scarcity and climate mitigation options. The concept of homegardens in Sri Lanka also provides interesting aspects to the debate and future research in terms of forest definitions and general sustainability.