摘要
【目的】混交林择伐技术对实现林分可持续经营至关重要。本文对择伐后的落叶松云冷杉林林分直径结构和生长动态变化进行研究,为科学进行择伐活动和合理调整林木径级株数结构提供参考。【方法】以落叶松云冷杉近天然混交林为研究对象,设置对照样地(0%)和轻度(20%)、中度(30%)、强度(40%)择伐样地各4块,利用伐后5~11年的观测结果,比较分析了不同强度择伐对落叶松云冷杉混交林林分结构及生长的影响。【结果】研究发现中度、强度择伐后落叶松云冷杉混交林断面积和蓄积生长率明显增大,表明择伐为林分中保留木创造养分空间,加速了林分胸径和蓄积的生长进程。伐后5~11年,对照样地和中度择伐样地Weibull分布曲线呈右偏,样地内中小径材居多,且中度择伐样地径级分布宽广;轻度择伐和强度择伐样地呈左偏分布,林分内中大径材较多。对照样地Weibull分布的c值变化不大,择伐样地c值随时间增加而增大,说明择伐去除劣势木,增加林分空间,林分结构得到优化。一定强度的择伐还能降低林分中林木的枯损率,而高强度择伐会增加林木风倒的风险。【结论】从可持续经营角度看,可根据不同经营目的选择适当的择伐策略。中度择伐后落叶松云冷杉林的林木生长速率明显增大,林分中林木径级较完整,林分结构稳定,林木枯损率减少,有利于林分生长的可持续发展。
[Objective] Thinning program is crucial to the management of mixed forests. The diameter structure and growth changes of larch-spruce-fir stand after selective thinning were studied in order to help creating better thinning programs and improve stand quality. [Method] Larch-spruce-fir mixed forests including 12 selective thinning plots with different thinning intensities(light,20%; medium,30%;heavy,40%) and 4 control(0%) plots were established. The effects of selective thinning and dynamic changes on diameter structure stand growth were analyzed based on stand inventory of the 5-11 th yearafter thinning. [Result] We found that medium thinning and heavy thinning had significantly increased the growth of basal area and stand volume,which conformed thinning program leading to faster stand growth because more space and nutrient were provided for standing trees after thinning. The diameter distribution(Weibull distribution) curves of control stand and medium thinning stand were right-skewed,which demonstrated small and medium trees dominated in these stands. While the diameter distribution curves of light thinning and heavy thinning stand were left-skewed which showed a higher number of bigger trees. The parameter c of Weibull function remained the same in unthinned stand,while it increased with time in thinned stands. This indicated thinning treatment optimized stand structure by removing inferior trees and increasing stand space. Simultaneously,thinning treatments could decrease tree mortality,however,heavy thinning increased the risks of wind throw. [Conclusion] Different selective thinning schemes can be applied to the forest according to the management goal. For sustainable management,medium thinning faster the stand growth,which also resulted in a stable diameter structure with higher DBH range and less tree mortality,hence medium thinning may promote sustainable forest development.
引文
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