Ralating Environmental Factors to Growth of Some Australian Tree Species at Different Sites in Thailand

Abstract

Height (Ht), diameter at breast height (DBH) and basal area (BA) growth of Eucalyptus camaldulensis, Acacia mangium and Acacia auriculiformis at three years of age were measured as well as climatic and soil conditions at over 180 plots at seven trial sites in Thailand. The results for Ht, DBH and BA showed highly significant differences among sites, but there were no significant differences among seedlots for all species. E. camaldulensis and A. auriculiformis showed generally high overall growth. E. camaldulensis grew particularly well at Si Sa Ket, whilst Sai Thong was the best site for A. auriculiformis. A. mangium grew poorly at all sites. Analysis of variance (ANOVA) was carried out for each year of planting with the growth of E. camaldulensis showing significant differences between years. Trees planted in 1987 grew more slowly than those planted in 1986 at both Sakaerat and Chanthaburi. Tree growth measurements were related to environmental factors using stepwise linear regression. The results of the statistical analyses showed that much of the variation in growth data could be explained by regression models including soil and climatic factors. The combined influence of all environmental factors in the models were shown by r² values. E. camaldulensis relationships produced high r² values of 0.70 or greater and similar r² values were obtained for most soil depths. A. mangium data produced highly variable r² values ranging between 0.26 and 0.85. A. auriculiformis data produced generally high r² values with values ranging between 0.65 and 0.91, with especially good relationships for Ht and DBH.