间伐强度对云南松中龄低产林分结构的调整研究

Effects of different intensity of thinning on the improvement of middle-aged Yunnan pine stand

2008年通过对禄丰村林场徐家山林区具有代表性的25 a生塘播云南松人工用材林进行本底调查,依据云南松的林分密度、林木平均胸径、云南松单株林木平均占据的面积和云南松的枯立木百分比等判断该林分为云南松的劣质低产用材林,确定抚育间伐是该林分改造的主要措施。选择相似立地条件的林地,在同一坡向(SE)分别以1 hm2为间伐单位,设置4个研究区,分别设为3块样地及1块对照样地,以研究区内原有林木株数控制进行间伐,间伐的强度样地分别为40%(样地1)、30%(样地2)、20%(样地3)和0%(对照),每个研究区选择林木生长均匀的900 m2(30 m×30 m)作为长期调查研究的标准样地。间伐结束进行第2次调查,1年后进行第3次调查。结果表明:处理1～3间伐前后林木胸径与对照相比,无论其平均值、最小胸径或林木的胸径集中分布范围的下限,均得到了明显的提高,胸径分布较为均匀。云南松的林分质量也相应的得到了提高,达到了间伐的效果。对照样地仅实施下层灌草清理和对部分天然更新的阔叶树伐除,故其云南松林木株数的胸径仍呈左偏态分布,胸径分布极不均匀,林木胸径的分布仍处于自然松散的状态。云南松间伐后,不但林木的胸径得到了普遍的提高,其平均树高也同样有一定程度的提高;但间伐后云南松林木平均高生长量的提高比例显著小于平均胸径生长量的提高比例。根据株数间伐强度20.5%～31.5%的林分间伐1 a后的各项指标分析,以31.5%的株数进行间伐有利于改善该类劣质低产云南松人工林的生长环境,促进林木生长。

In the survey of a 25 year old Yunnan pine artificial forest in Xujiashan plot in Lufengcun forest farm of Yuliang County was carried out in 2008. The forest was consided as low guality by evaluating its stand density, average DBH of the trees, area covered by single trees and the rate of eracted died trees inside plot, thus tending thinning was adopted as a major compliment of improvement. Four transects（three plots and one control） were set up oriented to southeast with treatments of 4 different intensity of thinning under the original density of the forest. The thinning was taken by a unit of 1 hm2 , and the transects were 30 m × 30 m （900 me ） and trees were approximately identical. The thinning intensities were 40% （plot I ）, 30% （plot II ） and 20 % （plot III ） 0 % （control）, respectively. The second survey was taken after the thinning finished and the third survey was carried out one year later. The results show that compared to ther control, the trees of all treatment the average DBH （diameter at breast）, minimal DBH and the lowest concentrated DBH range bad been improved significantly after the thinning, and the average height of the trees was also heightened. Among 4 intensities of thinning, the better performances were that of thinning intensity of 40% and 31.5%. While when they were 20.5% and 31.5%, the stands had tendency of becoming into mixed forest of needle and broadleaf trees and mainly of Yunnan pine, this might accelerate the succession and while in control plot,only the shnub and grass were cleared in addition with some broad-leaf trees, thus the pine trees presented with a left shewed normal distribution, showing an uneven and natural slack DBH distribution. Through the thinning intensity of 31.5%, the forest reached lowest mortality. It is concluded that the quality of the stand improved greatly by thinning, and specifically the effects were notably in low production forest of Yunnan pine, thinning intensity with 31.5% is recommended.