Environmental Factors Related to the Site Index of Siamese Rosewood Plantations in Thailand
Taengmoo Phunchaisri, Chongrak Wachrinrat, Ponthep Meunpong, and Suwan Tangmitcharoen
Environment plays an important role in the growth of a tree. In this study, we focused on searching for appropriate soil properties and climatic factors related to the site index equation and growth rate of Siamese rosewood (Dalbergia cochinchinensis Pierre ) in plantation around Thailand, using a stepwise multiple regression analysis. The results indicated that four types of soil textures exist which are sandy loam, loamy sand, sandy clay loam, and sand. However, the dominant soil textures were sandy loam and loamy sand. The site index was found to be correlated with the pH of both the topsoil and subsoil, at depths of 0-10 and 10-30 cm, while the mean temperature was the only climatic factor found to be correlated with the site index. The soil factor related to the absolute growth rate (AGR) was pH at both the topsoil and subsoil depths. However, the AGR at subsoil was also related to sodium while the relative growth rate (RGR) was not related to any soil variable at the topsoil level but related with porosity at the subsoil level. The temperature, humidity, and the number of rainy days were found to be related to AGR while only the temperature was related to RGR. A combination of soil and climatic factors was found to be related to pH, temperature and humidity with AGR of topsoil and subsoil. AGR at topsoil level was related to exchangeable potassium while only the temperature was related to RGR at both the soil depths.