桂西南杉木林分生长对间伐的动态响应

Growth response of a Cunninghamia lanceolata plantation to thinning in southwestern Guangxi,China

以广西凭祥14年生杉木Cunninghamia lanceolata人工林(保存密度为1 219株·hm-2)为对象,设置69%(处理Ⅰ),60%(处理Ⅱ),51%(处理Ⅲ),40%(处理Ⅳ)4个间伐强度处理和不间伐对照,定期观测间伐后9 a内胸径、树高、枝下高和冠幅等林分生长指标,并计算单株材积和林分蓄积,从而揭示林分生长对间伐的动态响应,筛选适宜的间伐强度,为杉木人工林近自然化改造提供技术支撑。结果表明:间伐强度显著影响杉木林分胸径、枝下高、单株材积和蓄积生长(P<0.05),对树高和冠幅的影响不显著(P>0.05);胸径和单株材积以处理Ⅲ为最高,枝下高和蓄积则以对照为最高。胸径、冠幅和枝下高年均增量在间伐后第1~3年最大,处理间的差异随着时间的推移逐渐缩小。树高、单株材积和林分蓄积年均增量高峰则出现在间伐后第3~5年。根据上述试验结果,为了快速培育杉木大径材,建议在杉木近自然化改造中选择间伐强度约50%(处理Ⅲ)为宜。

To reveal the dynamic response of stand growth to thinning treatments and to select suitable thinning intensities in Cunninghamia lanceolata（Chinese fir） plantations,a thinning trial was conducted in a 14-yearold plantation of C.lanceolata at Pingxiang City,Guangxi.Stand density was about 1 219 trees·hm^（-2）,and the experiment was arranged in a randomized complete block design with five treatments：four thinning treatments of 69%（Ⅰ）,60%（Ⅱ）,51%（Ⅲ）,and 40%（Ⅳ） and a control without thinning and four replicates for each treatment.Diameter at breast height（DBH）,tree height,crown base height（CBH）,crown width（CW）,individual tree volume（ITV）,and stand volume（SV） were determined with a circle samping plot of 400 m^2 for each replicateperiodically in 9 years after thinning.Results from one-way analysis of variance and Duncan＇s multiple range tests showed that thinning intensity significantly increased DBH and ITV,decreased CBH and SV（P0.05）.The highest DBH and ITV were observed in Treatment Ⅲ;whereas,the highest CBH and SV were in the control.The mean annual increments for DBH,CW,and CBH were highest 1 to 3 years after thinning with differences between treatments gradually declining as forest age increased;however,peaks for tree height,ITV,and SV growth occurred 3 to 5 years after thinning.Based on the above findings,a thinning intensity of about 50%（Treatment Ⅲ） should be applied for close-to-natural forest management so as to producelarge-sized timber of C.lanceolata more rapidly.