Synergistic Carbon-Biodiversity Gains in Diversified Rubber Agroforestry Systems, Southern Thailand
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Abstract
Rubber plantations cover millions of hectares across Southeast Asia, yet their capacity to deliver both agricultural production and ecological benefits depends heavily on how they are managed. This study compared six rubber management systems in southern Thailand, a conventional monoculture (RM) and five progressively diversified rubber-forest systems (RF1 to RF5), to quantify how increasing structural complexity affects biodiversity, soil health, and carbon storage. Field inventories documented tree species composition, natural regeneration, and deadwood; soil samples characterized organic carbon, nitrogen, and nutrient status; and aboveground biomass and carbon stocks were estimated using the TGO national carbon accounting tool. The most diversified system, RF5, supported 6.4 times more tree species than monoculture (205 vs. 32 species ha⁻¹) and three times the seedling regeneration (7,725 vs. 2,471 seedlings ha⁻¹). Soil organic carbon nearly doubled (from 1.44% to 2.49%), and total nitrogen increased significantly. Total non-rubber aboveground biomass rose nearly fourfold (from 622.64 to 2,348.57 kg ha⁻¹), and the associated carbon stock reached 4.04 tCO₂e ha⁻¹ compared to 1.20 tCO₂e ha⁻¹ in monoculture. These values represent only the diversified vegetation component; whole-system carbon stocks, including the rubber trees, are substantially higher. These gains moved together across the management gradient rather than independently, with soil fertility, biodiversity, and carbon accumulation reinforcing one another. Although diversified intensity and stand age co-vary in this cross-sectional design, the consistent coupling of ecological indicators across the gradient indicates that structural complexity is a primary organizing factor. Diversified rubber agroforestry systems offer a practical pathway for tropical smallholders to improve ecological function and contribute to climate mitigation.
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