Changes in soil carbon stocks under plantation systems and natural forests in Northeast India

Understanding the impact of land use conversion from forests to plantations on soil organic carbon (SOC) stocks is critical for sustainable land and forest management in Northeast India (NEI). The present study was conducted in West Garo hills district of Meghalaya state in NEI, to evaluate the impact of plantations (rubber, tea, areca nut, cashew nut and pineapple) on SOC stocks in comparison with a natural forest. Soil samples were collected from plantations of different age classes (0-5, 5-10, 10-15, 15-20, 20-25, 25-30, and 30-40 years old) to assess their potential for C storage. RothC model was run at equilibrium on forest land-use, and thereafter was calibrated and validated to model SOC stocks in the plantations over the 40 years chrono-sequence using the baseline average climate data. Results showed that with increase in age of plantations (at 40 years), SOC stocks decreased to 57.4, 50.3 and 44.4 Mg C ha (-1) in rubber, areca nut and pineapple plantations at the average rate of 0.41, 0.58 and 0.73 Mg C ha (-1) yr (-1), respectively. This corresponded to a SOC stock loss of about 22, 32 and 40% compared to the initial SOC stock under forest (73.6 Mg C ha (-1)). Conversely, SOC stocks in tea and cashew nut plantations increased to 83.4 and 75.4 Mg C ha (-1) (at the average rate of 0.24 and 0.05 Mg C ha (-1) yr (-1)), corresponding to a SOC gain of about 13 and 2.5% compared to that under forest over 40 years. The data on abrupt climate change (ACC) scenario by RothC simulations showed that rubber, areca nut, pineapple and forest land uses would lose carbon at the rate of 0.65, 0.65, 1.42 and 0.13 Mg C ha (-1) yr (-1), respectively. Conversely, tea and cashew nut plantations might gain C at the rate of 0.35 and 0.23 Mg C ha (-1) yr (-1), respectively, representing a valuableoption for storing C and mitigating and adapting to climate change. Further, protecting and restoring natural forests and/or mixed stands of native tree species might reduce the risks of the loss of biodiversity and be a viable option for sustainable land management in NEI.