Growth model of DBH and tree height for individual tree of natural secondary Phoebe bournei forest based on dummy variable

ObjectiveThe growth regularity and growth model of Phoebe bournei natural secondary forest were studied, which will provide the reference basis for its growth prediction and quality improvement management measures.

MothodTaking natural secondary Phoebe bournei forest in Anfu County of Jiangxi Province, eastern China as research object, the basic data were obtained by means of typical sample investigation and stem analysis. According to the level of competitive pressure, the analysic woods were divided into tree types. From low to high, they were type 1, type 2 and type 3, respectively. Growth regulation of Phoebe bournei was studied in this paper. Five kinds of theoretical growth equations with biological significance were selected, and the optimal basic model was selected according to the model goodness of fit and evaluation indexes. On the basis of the optimal model, the growth model of dummy variables with competition types was constructed.

Result(1) The stem analysis data showed that 30th−50th year was the main fast growing period of DBH, the maximum current annual growth was 0.57 cm. while that 35th−45th year was the fast growing period of tree height, the maximum current annual growth was 0.37 m. (2) The optimal basic model of DBH was Gompertz equation, the value of R² was 0.756 and the forecasting accuracy was 94.28%, and the value of R² and the forecasting accuracy of the optimal dummy variable model were 0.873, 95.71%, respectively. The optimal basic model of tree height was the modified Weibull equation, the value of R² was 0.856 and the forecasting accuracy was 96.54%, and the value of R² and the forecasting accuracy of the optimal dummy variable model was 0.882, 96.96%, respectively. (3) According to the growth curves of DBH and tree height under different competition types fitted by the constructed dummy variable growth model, the total increment of DBH and tree height showed that type 1 > type 2 > type 3, and the maximum DBH increment of type 1 was 1.6 times of type 3.

ConclusionThe competitive pressure has an effect on the growth of DBH and tree height of Phoebe bournei. The goodness of fit and estimation accuracy of dummy variable model with competition type were better than the basic model, which is beneficial to improve the accuracy and applicability of the model.