Manan Bhan , Chetan Misher, Ankila J. Hiremath, Abi Tamim Vanak

Land management changes threaten the ecological functionality of grassland ecosystems worldwide, including the ability of these ecosystems to store carbon in their soils. The Banni grasslands, Asia’s largest tropical grassland, is no different in this regard. Despite being a highly biodiverse ecosystem with an extensive land use history, information on soil carbon fluxes in this ecosystem remains conspicuously absent. In this study, we map soil organic carbon (SOC) stocks within the upper 30cm depth across land use-land cover (LULC) classes by combining high-resolution satellite imagery with field-based soil carbon data from a network of long-term monitoring sites. We find that Banni currently stores 27.69 MtC in its soils, with an average SOC density of 119.61 ± 3.50 tC/ha (Mean ± Std. Error). These estimates compare favourably with arid and semi-arid grasslands as well as seasonally-flooded savannas across the tropics. The highest SOC densities are found in restored grasslands (142.72 ± 5.72 tC/ha), reaffirming the potential of carbon recovery from ecological restoration. Tracing 10 years of LULC change in the region indicates the further expansion of the invasive tree Prosopis juliflora across the landscape, but its impacts on changes in SOC concentrations estimates remain varied. Our results indicate the large soil carbon storage potential and the SOC fluxes associated with woody encroachment in Banni, and point towards the need for the active management of Banni so that carbon benefits can accrue at meaningful timescales for reversing land degradation and contributing to land-based climate action.