Carbon stock assessment in home garden agroforestry systems of humid tropical regions

Abstract:

How much carbon do home gardens actually lock away in humid tropical landscapes? This research addressed that question by measuring carbon stocks across twelve home garden agroforestry systems in the Mekong Delta region of Vietnam. Gardens were grouped into three size classes: small (<0.1 ha), medium (0.1-0.3 ha), and large (>0.3 ha). Aboveground biomass was estimated through non-destructive tree inventories using species-specific allometric equations, while belowground biomass was derived from root-to-shoot ratios reported for tropical agroforestry. Soil organic carbon was determined at 0-30 cm depth following the Walkley-Black wet oxidation method. Total carbon stocks ranged from 78.4 Mg C ha⁻¹ in small gardens to 129.6 Mg C ha⁻¹ in large gardens. Soil organic carbon formed the biggest single pool across all size classes, contributing 48.7-54.5% of the total. Tree biomass carbon was the second-largest pool and rose sharply with garden size, reflecting higher stem density and the presence of mature timber species in larger plots. Shrub and herbaceous layers contributed modestly, together accounting for 5.8-10.5% of total stocks. A positive linear relationship emerged between species richness and total carbon stocks (R² = 0.73, p < 0.01). These results indicate that home gardens in humid tropical settings can store carbon at rates comparable to secondary forests, supporting their role in local climate-change mitigation efforts and providing a basis for their inclusion in community-level carbon-offset programmes.