Recovery of Soil Organic Carbon During Forest Fallow Following Shifting Cultivation in the Eastern Ghats and North-East Hill Region of India

Shifting cultivation is conducted by many tribes inhabiting tropical and sub-tropical regions around the world. In India, it is prominently practiced in the Eastern Ghats and North-east hill region states. The major environmental effects of shifting cultivation are loss of forest cover, accelerated soil erosion and land degradation. However, these negative effects are ameliorated by the fallow period which offers the opportunity for recovery of the vegetation and soil fertility. This study aimed to assess the soil organic carbon (SOC) dynamics in the shifting cultivation fallow system and to evaluate the optimum fallow length for SOC recovery. During the study, we quantified the rate at which SOC stocks to 0.5 m depth recovered among fallow periods of increasing age. We measured and compared SOC stocks in natural forest, current shifting cultivation, and seven different aged fallow sites covering a broad range of biophysical conditions across seven locations in three Indian states. Short term cultivation after clearing the natural or secondary forest resulted in sharp declines in the SOC stocks across all locations, with a loss of 55–71% in the Eastern Ghats and 39–41% in the North-east hill region. The recovery of SOC showed a positive relationship with the fallow duration. In the Eastern Ghats, after 50 year fallow periods, SOC stock recovered 60–86% in comparison to the natural forest’s SOC. The recovery of SOC was faster in North-east India as SOC recovery after 50 years of fallow was comparable to the natural forest SOC stock. We conclude that recovery of SOC stocks showed a positive relationship with the fallow duration but the rate of recovery varied with topographic and climatic factors. During the recovery process, the adjacent natural forests act as seed source and directly contribute to the vegetation establishment and the more rapid recovery of SOC stocks. Among the study sites, SOC stock recovery was significantly faster in the North-eastern hills than the Eastern Ghats.