Quantification of carbon stock and tree diversity of homegardens in a dry zone area of Moneragala district, Sri Lanka

摘要

Homegarden agroforestry systems are sug- gested to hold a large potential for climate change mitigation and adaptation. This is due to their multifunc- tional role in providing income, food and ecosystem services while decreasing pressure on natural forests and hence saving and storing carbon. In this paper, above- ground biomass carbon and tree species diversity of trees was quantified in homegardens around two villages in the dry south-eastern part of Moneragala district of Sri Lanka. A total of 45 dry zone homegardens were sampled on size, diameter at breast height, tree height and species diversity. Using allometric equations, we find a mean above-ground biomass stock of 13 mega grams of carbon per hectare (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 and composition between individual homegardens. Mean above-ground carbon stock per unit area was higher in small homegardens (0.2 ha, 26 Mg C ha-1, n = 11) and statistically differ- ent compared to medium (0.4–0.8 ha, 9 Mg C ha-1, n=27) and large (1.0–1.2ha, 8MgCha-1, n=7) homegardens. In total, 4,278 trees were sampled and 70 tree species identified and recorded. The Shannon Wiener index were used to evaluate diversity per homegarden and ranged from 0.76 to 3.01 with a mean value of 2.05 ± 0.07 indicating a medium evenly distributed diversity of sampled tree species. The results show a vast heterogeneity in terms of carbon stock and tree diversity within the less studied dry zone homegar- dens; results that contribute to more knowledge of their expansion potential as well as climate mitigation and adaptation potential. The results are also useful for whether homegardens should be considered to be included as an activity to enhance natural forest cover within Sri Lanka’s newly commenced UN-REDD National Programme.