Diameter and Height Distributions of Natural Even-Aged Pine Forests (Pinus sylvestris) in Western Khentey, Mongolia
The purpose of this study was to find a suitable probability density function (PDF) to model the diameter at breast height (dbh) and height distributions of even-aged pine (Pinus sylvestris L.) forests. For the study, three different age-classes (AGs) of pine forests were used. Burr, Dagum, and Johnson SB distributions were applied due to their flexible properties. Result showed that dbh distributions of the 10~15- (AG1) and 40~45-yr (AG2) stands were left-tailed, while the 60~65- yr (AG3) stand was normally skewed. Height distributions of the AG1 and AG3 stands were left-tailed, while that of the AG2 stand showed no obvious distribution shape, due to its discrete height distribution. A distribution study revealed that in left-tailed forests, dbh and height distribution shapes were best approximated by the Dagum distribution. In the case of the normal distribution shape, the Johnson SB was better than the Burr and Dagum ones. Based on these results, we concluded that dbh distributions of even-aged AG1 and AG2 forests were heavily left-tailed, and the forest structure tended to normal for the AG3 forest. The height distribution is left tailed (AG1 and AG3) if a forest's height growth is not constrained by space, while it will become discrete in a high-density stand (AG2).