思茅松天然林林分直径结构动态变化

基于云南思茅松连续5期森林资源清查数据,采用偏度、峰度、直径变动系数、径阶株数分布及直径累积分布等指标对其天然林林分直径结构动态变化规律及其密度效应进行探讨。结果表明:在10～70 a内,偏度先为正值,后由正值逐渐趋向于负值,直径分布曲线表现为先左偏后右偏,偏度绝对值先变小后变大,密度高的林分其偏度值大;峰度随林分年龄的增长呈下降趋势,随着林分密度的增大,林分直径分布曲线峰度值依次增大,且不论林分密度高低,峰度值都趋向于0;直径变动系数随林分年龄的增长总体呈下降趋势,受密度影响不明显;对于任一相同的株数累积分布,密度越高的林分所对应的直径区域中值越小;林分径阶株数分布直观地说明了上述结论。

Studies on Dynamics of Diameter Structure of Pinus kesiya var. langbianensis Natural Stands

The dynamics of the diameter structure of Pinus kesiya var.langbianensis natural stands and the density effect of the stands were studied with the criteria including skewness,kurtosis,diameter variance coefficient,cumulative diameter distribution curves and frequency distribution based on the data from five periodical forest resource survey on P.kesiya var.langbianensis in Yunnan Province.The results showed that in the 10-70 a age classes,the skew value of the stands changed gradually from positive to negative,the absolute value of the skew index changed from small to bigger,and the stands with high density had bigger skew value.The value of kurtosis showed the downtrend with the increase of stand age.The kurtosis value of the stand diameter distribution increased as the stand density increased.No matter how the stand density changed,the value of kurtosis all tended to 0 at last.The study showed that the diameter variance coefficient generally decreased along with the increment of stand age,and it was not obviously influenced by stand density.At any range of cumulative frequency distribution,the smaller the density was,the bigger the middle value of diameter class was.The size-class distribution directly testified these conclusions.