Influence of environmental factors on the distribution of tree species in deciduous dipterocarp forest at San Sai Forest Reserve, San Sai District, Chiang Mai Province

Abstract

This research was aimed to study the environmental factors influencing the distribution of tree species in the natural deciduous dipterocarp forest (DDF) in The San Sai Forest Reserve, Chiang Mai Province. 15 survey points were set up systematically 200 m apart. Each survey point contained 3 sampling plots of 30 m x 30 m in size, and each plot was 50 m apart. All tree species with diameter at breast height (DBH) larger than 1 cm were identified and measured in 2020. Species composition was analyzed using stand clustering analysis. One-way ANOVA was used to determine differences in environmental factors among groups, and to elucidate the relationship between these factors and tree species distribution parameters. The results showed that 51 species from 37 genera and 27 families were found. The soil in the area was mainly composed of sand particle (more than 50%). Cluster analysis of tree data based on 60% similarity index revealed five groups of tree stands, which were Dipterocarpus tuberculatus stand, Shorea obtusa stand, Shorea siamensis stand, Dipterocarpus obtusifolius-Shorea siamensis stand and Dipterocarpus obtusifolius-Shorea obtusa stand. The species diversity value was found the highest in Shorea siamensis stand (39 species), which was significantly influenced by the distance from natural water source. However, other factors did not affect stands clustering. Analysis of factors influencing species distribution showed that 12 out of 51 species were found to be associated with 9 environmental factors. Proportion of clay particle in the soil strongly influenced tree distribution. Based on types of responses, trees could be grouped into those that preferred either high or low percentage of clay and those that were not affected by percentage of clay. The relationships between plant distribution and environmental factors are very important for restoration management plans. The selection of suitable species based on their niches is needed to promote successful restoration programs.

Keywords: ecological niche, deciduous forest, tree stand clustering, forest reserved