择伐对天然云冷杉林林分生长和结构的影响

摘要

Twenty plots in natural spruce-fir forests, after initial selective cutting with different intensity (control,20％ , 30％ , 40％ ) , were set to study effects of the different cuttings on stand growth and structure in a few year when the second cutting was conducted, and changes of stand growth and structure in different recovery periods with 2 -4 more cuttings after the initial cutting were analyzed in this paper. Results showed that the annual growth rates of stand DBH and volume after the initial selective cutting were higher than that of un-cutting control stands. After the initial cutting they gradually increased, and then the rates began to decline in 4 -6 years, until to the next cutting. The annual growth rate of stand volume in the plots with the initial cutting of 20 ％ was not significantly different from the plots with cutting intensities of 30 ％ and 40 ％ in 6 years, but the annual growth rate of DBH in plots with the cutting intensity of 40 ％ increased significantly. The annual growth rates of stand DBH and volume in plots with the cutting intensity above 30 ％ were relative high with maximum value of 2.6 ％ and 8.7 ％ respectively. The annual growth rates of stand DBH and volume were higher in plots carried out with 2 - 4 reasonable cuttings than that of plots with only one cutting or no cutting,and the annual growth rates of stand DBH and volume in 2009 reached to a maximum value of 3.6 ％ and 5. 5 ％ respectively. The stand diameter class distribution in all the plots with the initial cutting changed from inverse J-shaped to asymmetric single or multi peak curve over the time. With reasonable cutting cycles ( in about 8 years) and intensity ( about 20 ％ ), stands after 2 -4 cuttings could keep a better diameter class structure. By fitted to a negative exponential model, the values of parameter K and a for all plots mainly presented a reduction trend over the time after selective cutting.%以20块经过抚育的天然云冷杉林样地为研究对象,分析第2次择伐前不同初始择伐强度(对照、20%、30%和40%)对林分生长和结构的影响,以及初始择伐后不同恢复时间(期间进行2～4次择伐)林分生长和结构的变化.结果表明:初始择伐后的样地林分平均胸径和蓄积的年生长率相对高于对照样地,采伐后开始增加,4～6年后减小直至下次采伐;初始择伐后6年20%强度的林分蓄积年生长率与30%和40%差异不大,但40%强度择伐后的林分平均胸径年生长率显著增加;30%强度以上择伐后的林分生长相对较快,胸径和蓄积年生长率最高分别达2.6%和8.7%;经过合理的2～4次择伐的林分平均胸径和蓄积的年生长率相对高于仅1次择伐和未择伐的林分,2009年最大值分别为3.6%和5.5%;随着初始择伐后时间的增加,各样地林分径级分布由初始的反"J"型向不对称的单峰或多峰山状曲线变化;但经2～4次择伐的样地,只要控制合理的采伐周期(6年左右)和强度(20%左右),就能保持较好的径级结构;通过负指数分布拟合发现,各样地的κ值和α值随着伐后时间延长基本呈减小趋势.