Influence of altitude on tree species diversity, structure and composition in a protected area of the Eastern Himalayas, Mizoram, India

Deciphering the composition, structure, and diversity of tree communities is crucial for effective forest ecosystem conservation, particularly as climate change accelerates. However, basic knowledge of forest structure and composition remains limited in remote areas of the Eastern Himalayas. This study aimed to examine the diversity, structure, and composition of tree communities along an altitudinal gradient in Phawngpui National Park, Mizoram. The study site was stratified into three altitudinal zones: Low Altitude Forest (273–900 m), Mid Altitude Forest (900–1500 m), and High Altitude Forest (1500–2157 m). The data was collected using the random stratified sampling method. In each altitudinal zone, 40 plots of 100 m² were established, in which all individual trees having at least 10 cm DBH (diameter at breast height), which is 1.3 m above the ground, were measured and recorded in the field. A total of 107 tree species, distributed among 78 genera and 39 families, were recorded. The family Fagaceae and its species Castanopsis tribuloides dominated the forest. The non-metric multidimensional scaling (NMDS) analysis showed that species composition varied across altitudinal zones. Stem density, basal area, and stem DBH were highest in the MAF zone. Size class distribution showed a reverse J-shaped curve, indicating uneven-aged forest. Species richness and diversity exhibited a hump-shaped pattern. While alpha diversity followed a unimodal pattern, beta diversity exhibited a contrasting trend. This study will help understand the relationship between forest attributes and altitude, enhancing the design of efficient conservation and management plans.