Homegardens as a modern carbon storage: Assessment of tree diversity and above-ground biomass of homegardens in Matale district, Sri Lanka

Homegardens are principally known as integrated man-made ecosystems with annuals and perennials where trees play a significant role in storing atmospheric carbon in the vegetation as above-ground biomass (AGB). Being one of the agroforestry systems, homegardens could ease the pressure on natural forest cover in the process of carbon sequestration and carbon storage, while reducing the greenhouse gas accumulation (CO₂) in the atmosphere. Thus, they could be described as a promising approach for mitigation of climatic changes. A study was conducted to assess the tree diversity and AGB carbon stock of homegardens in Matale district, Sri Lanka. A total of 122 homegardens ranging from urban dwellings up to natural eco-systems across 05 agro-ecological regions (AER) were surveyed, capturing a vast diversity. A total of 5140 woody trees were recorded from 100 genera and 45 families, covering 16.67 ha of homegardens. Six and three tree species were identified as vulnerable and near threatened, respectively in terms of national-level conservation status. Shannon-Wiener index (SWI) of 1.90 ± 0.49 ranging between 0.49 and 2.83 indicated compositional diversity of the tree species. The AGB was widely varying between 0.8 and 139.4 Mg C/ha (mean AGB of 36.5 ± 27.4 Mg C/ha). AGB and SWI were higher in small-scale (38.8 ± 29.7 Mg C/ha and 1.91 ± 0.50, respectively) than in medium-scale homegardens (28.0 ± 14.9 Mg C/ha and 1.86 ± 0.50, respectively). Species richness and number of species per hectare were higher in small scale (<0.2 ha) homegardens compared to medium scale (0.2–0.8 ha). A considerable variation of tree diversity and AGB was observed among the homegardens in different AERs. The variation of AGB was primarily governed by tree density (trees/ha) and species diversity. Focusing on that, optimizing the potential of homegardens in terms of storing atmospheric carbon as AGB in the study area can be considered as a timely strategy in mitigating impacts of climate change and assisting domestic food security.