林农复合系统中林分直径分布动态研究

<正>通过对“林—农”复合经营系统中落羽杉密度试验林连续8年的定期测定,结果表明:林分平均单株胸径增长速率随密度增加和时间的推移,密度效应作用强度越来越大;单位面积林木总断面积值随密度的增大而增加,断面积密度R值随时间的推移也相应增大。描述直径分布动态规律的偏度指标K值,在林分未进入郁闭前,多数在零值附近摆动,较多地出现负偏。用正态分布模型更适于未进入郁闭阶段的落羽杉林分直径分布的数值拟合。

IAMETER DISTRIBUTION DYNAMICS OF STANDS IN AGROFORESTRY SYSTEM

The study has been conducted for eight years in the density test stands of baldcypress (Taxodium distichum Rich) which were established for agrofore-stry research. Measurements have been made at regular time every year. The result indicates that the denser the stand is, the stronger the average growth rate of diameter is influenced with the stand aging. when the stands ranging from 825 to 3330 trees per hectare are 8 years old, the diameter growth declines with the stand densifing. The stand of 3330 trees per ha has a keen competition. The basal area of stands per unit increases with densifing. The basal area density rises also with stand aging. The basal area density and basal area of the stand of 3330 trees per ha have nearly reached the up-limit. The majority in the skewness values of diameter distribution fluctuate around zero negatively, or positively, and more are negative. This paper presents three models of We-ibull, (3 and normal distribution for characterizing diameter distribution dynamics. The normal distribution provides best fit in unclosed stands.