A preliminary study of changes in forest stratification along environmental gradients in Southeast Asia

Changes in forest stratification along environmental gradients in Southeast Asian forests were studied, by applying Quantification Method I to the records of tree height inventories and environmental conditions in 29 study forest stands. To stratify individual trees into subpopulations in a stand, an empirical and graphical method was used. After stratifying all the component individuals of the stand into subpopulations, the number of subpopulations per stand and mean tree height per subpopulation were calculated and adopted as indices of forest stratification. Of the two indices, the latter index changed linearly with respect to the maximum tree height in the stand. Hence, the number of subpopulations and the maximum tree height as a substitute for mean tree height per subpopulation were biotic dependent variables in the application of Quantification Method I, while abiotic independent variables were the following six categorized environmental factors: the number of wet months with over 100 mm month⁻¹ rainfall in a year, occurrence of fog, mean annual temperature, magnesium accumulation in mineral soil, soil water drainage, and forest fire. It was concluded that these biotic and abiotic variables were the components of multivariate regression models, which successfully explained the development of forest stratification in terms of habitat conditions.