Forest Structure and Tree Species Diversity along an Altitudinal Gradient in Doi Inthanon National Park, Northern Thailand

A study on forest vegetation along an altitudinal gradient was conducted in Doi Inthanon National Park, Chiangmai, Thailand. The purpose of the study was to elucidate how community characteristics change from lowland to mountain vegetation in the tropical monsoon climatic zone in mainland Southeast Asia by using floristic composition and species abundance data collected from forty five plots at different altitudes and forest types. Community classification by cluster analysis suggested 45 sample stands to be classified floristically into three forest zones along an altitudinal gradient: (1) lowland forest (400-850 m asl) composed of 2 forest groups: (a) deciduous dipterocarp forest group dominated by Shorea siamensis, Canarium subulatum, and Shorea obtusa and (b) mixed deciduous forest group dominated by Teetana grandis, Xylia xylocarpa, Lagerstroemia calyculata, and Millettia leueantha. (2) Transition forest (850-1,400 m asl), in the intermediate zone between the lowland and montane zones composed of 2 forest groups: (a) pine-dipterocarp forest and pine-oak forest groups dominated by Pinus kesiya, Dipterocarpus tuberculatus, Aporusa villosa, Wendlandia tinctoria, Schima wallichii, and Helicia nilagiriea and (b) lower montane forest group dominated by Schima wallichii, Castanopsis /erox, Castanopsis tribuloides, and Helicia nilagirica. And, (3) montane forest (1,400-2,500 m asl), in the uppermost zone composed of 2 forest groups of both montane forest dominated by (a) Mastixia euonymoides, Castanopsis calathi/ormis, and Drypetes indica and (b) Neolitsea pallens, Actinodaphne henryi, and Rapanea yunnanensis. Tree density and basal area increases with rising altitude. Diversity of trees sharply increases from the lowland zone to an altitude of 1,800 m asl and gradually decreases at an altitude above 1,800 m asl shown by low species richness indices at high altitudes. In contrast, evenness indices were not greatly different along the altitudinal gradient.