Soil Organic Carbon Dynamics during Shifting Cultivation –Forest Regrowth Chronosequence in Eastern Ghats and North-Eastern Hills of India

Abstract

Shifting cultivation (Jhum) is widely practiced by tribes in tropical and subtropical regions worldwide. This system is predominant in the Eastern Ghats and North-Eastern states of India. Although this practice leads to deforestation, soil erosion, and land degradation, the fallow period offers an opportunity for vegetation and soil fertility recovery.

This study aimed to assess soil organic carbon (SOC) dynamics during the fallow period and determine the optimal fallow length for SOC recovery. The SOC stock recovery rates down to 0.5 m soil depth were quantified among different treatments involving fallow periods of increasing age, abandoned after the practice of shifting cultivation. Seven different-aged fallow sites (ranging from 5 to 50+ years) across seven shifting cultivation locations representing three different states were selected, and the SOC stocks in these sites were compared with those in natural forests and current shifting cultivation sites. Results showed that short-term cultivation after clearing natural or secondary forests sharply decreased SOC stocks, with losses in SOC to the tune of 55–71% in the Eastern Ghats and 39–41% in the North-Eastern states. The SOC recovery showed a positive relationship with fallow duration. In the Eastern Ghats, after 50-year fallow periods, SOC stock recovered 60–86% compared to natural forests. Recovery was faster in North-East India, with 50-year fallow SOC comparable to natural forest stocks. The study demonstrated that SOC stock recovery positively correlates with fallow duration, but recovery rates vary with topographic and climatic factors. During recovery, adjacent natural forests act as seed sources, contributing to vegetation establishment and faster SOC stock recovery. The findings suggested that among the study sites, SOC stock recovery was significantly higher and faster in the North-Eastern Hills than in the Eastern Ghats region.