Do carbon stocks and floristic diversity of tropical homegardens vary along an elevational gradient and based on holding size in central Kerala, India?

Homegarden (HG) agroforestry combines biological carbon (C) sequestration with biodiversity conservation outcomes. Although C stocks and species richness of HGs vary along elevational gradients and as a function of holding sizes, there is no consensus on the nature and magnitude of such variations. Field studies were conducted in the Western Ghats region of central Kerala, India (180 homesteads in 20 selected panchayats), to evaluate the effects of elevation (near sea level to 1938 m) and garden size (162-10,117 m) on aboveground C stocks and floristic diversity. The C stocks (per unit area) of HGs (arborescent species) were highly variable (0.63-93.65 Mg ha), as garden management was highly individualistic and it exhibited a weak negative relationship with elevation. Likewise, there was a weak negative relationship between C stocks and garden size. Tree stocking levels (stems/garden) and species richness (species/garden) positively impacted total C stocks per garden. Floristic diversity was high in the study area (753 species) and included many rare and endangered species (43 IUCN Red-Listed species) making homegardens reservoirs of biodiversity. Elevation and holding size exerted a weak negative linear relationship on Simpson's floristic diversity index, which ranged from 0.26 to 0.93 for the arboreal species. Homegardens, regardless of elevation or size, contribute to C sequestration and agrobiodiversity conservation and help achieve the UN Sustainable Development Goals (SDGs), particularly Climate Action (SDG-13) and conserving agrobiodiversity (SDG-15, Life on Land).