竹木混交林改为毛竹纯林经营后的林分生长动态

Growth Dynamics of Pure Phyllostachys pubescens Stands Transformed from Mixed Stands

对分别在1974年和1984年实施清除混交乔、灌木,把原竹木混交林改为毛竹纯林经营的两片毛竹林分内,于1985年各设立固定标准地20块,自1985年至1995年对改造后处于自然肥力条件下的林分不同生长阶段的毛竹纯林的生长指标,进行为期11a的观测,结果表明:在竹木混交林改成毛竹纯林后的较长经营期中,各生长因子的变化过程表现出明显的阶段性,即:新竹个体数量增长和粗度下降期(1～4a),主要特征是林分年新成竹数量迅速增加,4a中平均比改造前混交林内的增加50％,井在第3年时达到96株/600m^2的成竹峰值,且该时期新竹粗度低于混交林时的水平,但新竹产量上升;新竹粗度和产量上升期(5～11a),其间林分新成竹的平均粗度和产量逐年增加,在第11年时新成竹粗度和产量分别比改造前增大10％和52％,此间,年新成竹数基本稳定;新竹粗度和产量下降期(11～21a),这一时期新竹平均粗度和产量呈下降趋势,平均粗度在第21年时比第11年时下降3.9cm,同期内产量下降17％,表明该时期内出现较明显的林分生产力下降现象。

40 fixed experimental plots were set up in two bamboo stands in 1985, in which the two pure Phyllostachys pubescens stands were transformed from mixed stands in 1974 and 1984,and the growth observation of the new culm in the two mixed stands at differ- ent stages had been done from 1985 to 1995 so as to find out their growth dynamic. under natural fertility at different stages after they were transformed. The results were as follows: during the observed 11 years the growth of the stands can be divided into three stages of the yearly new culm and their diameter variation,i. e. ,first stage occurred in the 1st year to 4th year, in which the number of yearly new culm increased about 50% more than that in the mixed stand and reached a peak (96 new culm/(600 m^2. year)) in the 3rd year,and the diam- eter of yearly new culm decreased during the period but the output of new culm increased yearly;the second stage was from the 5th to 11th year in which the mean diameter and output of new culm kept at a stable level,and the mean diameter and output in 11th year was 10% and 52% more than those in the mixed stands, respectively; the third stage was from 12th to 21st year in which both the mean diameter and the number of new Culm declined yearly and resulted in yearly decreased output, and the mean diameter in the 21st year decreased by 3. 9 cm and output decreased by 17% as those in the 11th year,which showed the degradation of stands occurred in the pure bamboo stands during this period.