Dominant diameter growth model and Site Index Curves for certified Acacia forests in Thua Thien Hue province, Vi-etnam

Site quality evaluation is considered an important aspect of forest management, whereby forest managers can assess potential forest stand timber production for a particular species or forest type. The dominant diameter growth models and site index curves were developed to assess the site quality of certified Acacia forests in Thua Thien Hue province, Vietnam. In this study, the correlation between dominant diameter (Dgo) and diameter at breast height (DBH) was selected from four common correlation function forms: linear, power, exponential, and parabolic function. In addition, Schumacher and Korf growth functions were used to select and develop the most suitable site index curves. to evaluate the developed models, the coefficient of determination (R^2) and root mean square error (RMSE) were used as statistical criteria. The study investigated 50 sample plots of certified acacia forests from age 2 to age 10 in Thua Thien Hue to develop the models and other 20 sample plots were used to evaluate the developed models. The results showed that the dominant diameter had the best correlation with diameter at breast height in the form of a logarithmic function(Dgo = 8.8446*ln(DBH) – 7.0985). Meanwhile, the Schumacher function with equation Dgo = 24.366. e^(-4.193/A^1.2) is best describes the relationship between dominant diameter and forest age. Certified Acacia plantations in Thua Thien Hue province can be divided into three soil classes based on the diameter of dominant trees at age 5. The site index (according to dominant diameter) for good soil class (I), average soil class (II), and poor soil class (III) at age 5 are 14 cm, 12 cm, and 10 cm, respectively.