Comparative biomass carbon storage, CO2 mitigation potential and green economy valuation of polyculture and monoculture plantations under the Jan Van Yojna social forestry scheme in semi-humid tropical Jharkhand India

Tropical forest plantations under community-based schemes represent an underexplored yet critical nexus between land-use policy, climate change mitigation, and green economy valuation. This study provides the first quantitative assessment of biomass carbon storage, CO 2 mitigation potential, and carbon credit value for two contrasting Jan Van Yojna (JVY) plantation sites in the semi-humid tropical region of Ranchi district, Jharkhand, India: a seven-species polyculture stand at BUDMU (652 trees, 2.2 acres) and a monoculture Tectona grandis stand at ANGADA (500 trees, 2.0 acres), both established in 2016. Carbon stocks were quantified using field measurements of diameter at breast height (DBH), Forest Survey of India (FSI) regression-based volume estimates, species-specific wood density, modified Walkley–Black titration for determination of the carbon factor, and the IPCC Tier-1 methodology for conversion to CO 2 equivalents (CO 2 e), using a conversion factor of 44/12 = 3.667. The BUDMU polyculture site sequestered a total of 15.32 tonnes of carbon (56.19 tonnes CO 2 e; 17.21 t C ha −1 ), with Gmelina arborea (Gamhar) as the dominant species contributing 58.80% (33.04 tonnes CO 2 e), followed by Tectona grandis (18.44%; 10.36 tonnes CO 2 e) and Dalbergia sissoo. (10.92%; 6.14 tonnes CO 2 e). The ANGADA monoculture stored 5.92 tonnes carbon (21.71 tonnes CO 2 e; 7.31 t C ha −1 ), exclusively in Tectona grandis. In this paired case comparison, BUDMU’s whole-site carbon stock was 2.59× higher than ANGADA’s, and 2.35× higher on a per-hectare basis; this difference is associated with, though not statistically isolated from, species composition, and in particular the presence of the high-biomass Gmelina arborea. Per-tree Tectona carbon density was marginally higher in the mixed stand (12.28 kg/tree vs. 11.84 kg/tree), consistent with, though not directly tested by this study, a hypothesised facilitative inter-specific effect. Component-wise analysis revealed stem dominance in most species (stem root branch leaf), with exceptions in Swietenia macrophylla and Emblica officinalis (branch stem root leaf). Under three market-price scenarios, the hypothetical, not currently verified or tradable, carbon-credit value of the sequestered CO 2 e ranges from USD $280.93–$842.79 for BUDMU and USD $108.56–$325.68 for ANGADA under Voluntary Carbon Market (VCM) pricing; combined potential value under India’s Green Credit Programme (GCP) is ₹50,634 These case-comparison findings are consistent with a climate-mitigation and green-economy advantage for the polyculture design over the monoculture design at these two sites, with cautious implications for REDD+ baselines, Jharkhand’s State Action Plan on Climate Change, and biodiversity-stacked nature-based-solutions (NbS) finance in the Indian tropics. These findings derive from a single paired-site case comparison without plantation-level replication (n = 1 per plantation type; plantation type and site are confounded).