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

ZENG Ji;LEI Yuancai;CAI Daoxiong;TANG Jixin;MING Angang;Experimental Centre of Tropical Forestry,Chinese Academy of Forestry;Research Institute of Forest Resources Information Techniques,Chinese Academy of Forestry;  
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.
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