Tree species composition and diversity in abandoned Jhum lands of Mizoram, North East India

Abstract

Shifting agriculture system (locally known as Jhum) is the main driver of deforestation and forest degradation in north eastern region. This system has been extensively practiced to sustain the livelihood in rural areas of Mizoram which possesses serious threats to forest ecosystem and soil fertility. The course of vegetation development in secondary forest in abandoned fallow is a major concern to understand the process of succession in different fallow length. This study was undertaken in Aizawl and Mamit districts, Mizoram with the objectives to determine the tree species diversity, richness and abundance in different fallow periods. Fallow ages of 2–5 years (F₅), 6–10 years (F₁₀), 11–20 years (F₂₀) and 21–30 years (F₃₀) were selected with a total number of 37 sites and two circular plots of 12.6 m were laid in each site to carry out extensive enumeration and analysis of tree species. A total number of 91 tree species and 38 families were recorded. The number of trees increased by 47% from F₅ to F₁₀ but the same was decreased by 35% from F₁₀ to F₃₀. Ecological indices indicate high diversity and species richness in F₁₀ and F₃₀ compared to F₅ and F₂₀. The basal area significantly increased with the length of fallow period. The average girth at breast height (GBH) in F₅ was 30 cm but in F₃₀, the GBH increased to 130 cm. The dominant species changed as fallow period increased e.g. F₅ was dominated by Castanopsis tribuloides, F₁₀—Rhus chinensis, F₂₀—Macaranga denticulata and F₃₀—Albizia chinensis. The changes in dominant species with respect to fallow ages in the present study could be due to large anthropogenic disturbance on the pioneer species as well as greater establishment ability of the climax species in relation to its environment, altitude and soil condition.