Why Correct: Shifting cultivation (jhum) directly causes deforestation and soil degradation in Nagaland by clearing forest vegetation through slash-and-burn methods, exposing soil to erosion and reducing fertility over successive cycles.
Distractor Analysis: Insurgency creates security challenges but does not directly cause mountain barrenness. Urbanization affects limited valley areas rather than widespread mountain slopes. Rapid population growth increases pressure on land but operates primarily through expansion of shifting cultivation practices.
Takeaway: Traditional jhum cycles of 15-20 years have shortened to 3-5 years in many Naga areas, preventing adequate soil recovery and leading to permanent vegetation loss on steep slopes.