Influencing Factors Of Diameter At Breast Height Growth Of Pinus Sylvestris Var. Mongolica On Sandy Land

In this study,the artificial sand-fixing forest of Pinus sylvestris var.mongolica in the Zhanggutai area was used as the research object,the tree height and DBH data of the Pinus sylvestris var.mongolica plantation in the 35-standard land of the 10-60-year period in Zhanggutai area and the DBH of 14 analytical trees were used,the data,as well as the collected climatic factor data from 1973 to 2016,established 19 basic tree height-diameter growth models and 8 forest age-diameter growth models.After screening and testing,the tree height-diameter growth model and the forest age-diameter growth model with the best fitting effect were selected.The main climatic factors affecting the growth of Pinus sylvestris var.mongolica forest were screened,and the main climatic factors were analyzed by regression analysis to establish a regression equation between climatic factors and DBH growth.The conclusions are as follows:?1?The distribution of the diameter of the thoracic diameter is normally distributed.As the age of the forest increases,the distribution curve of the diameter of the thoracic diameter of each forest age shifts.The distribution trend of the diameter of the Pinus sylvestris var.mongolica plantations in different ages was consistent with the growth status.The larger the span of the diameter step,the more complete the differentiation of the breast diameter.Under the condition of 95%confidence interval,the calculated Richards equation for the growth process of Pinus sylvestris var.mongolica is y=0.302(1-e^-0.062t)^6.326,and the fitted parameters are consistent with the growth law of Pinus sylvestris var.mongolica.The annual growth reached the maximum,the number of mature age was 48 a,and the initial and ending ages of the fast-growing period were15.4 a and 44.1 a,respectively.?2?The Richards model is the optimal model for height-diameter growth of the basic tree.The function expression is:H=1.3+a?1-exp?-bD??^c,and its parameter estimation result is:a=11.593,b=0.146,c=3.151,which can well describe the relationship between the height-diameter of Pinus sylvestris var.mongolica.?3?For the forest age-diameter diameter growth model,the Gompertz model is optimally fitted.The growth function expression is:D=aexp?-bexp?-cA??,and the parameter estimation result is:a=24.043,b=1.990,c=0.046,R²=0.942,the fitting accuracy is high,which can well describe the growth process of Pinus sylvestris var.mongolica.?4?Introduce climate impact factors?temperature,precipitation?into different parameters of the optimal DBH model for environmental interpretation.In addition to the annual average temperature introduced to the three parameter combination position model fitting is optimal,the remaining factors are introduced to the two parameter combination position to best fit the DBH growth model.The order of influence of each factor on the DBH growth model is:average temperature in the growing season>dryness>annual precipitation>5-9 month dryness>warm index>the coldest month average temperature>the average annual temperature>the average precipitation in the growing season the amount.