抚育间伐对杉木人工林生长及出材量的影响

间伐对人工林生长及木材质量具有重要影响。在浙江开化开展了间伐强度（强度、中度和对照）和间伐方式（间伐1次，间伐2次）对杉木人工林生长及出材量等的影响研究，第1试验区大径材培育林分在第7年和第14年进行了2次间伐，第2试验区中径材培育林分仅在第12年时进行1次间伐。结果表明：22年生大径材培育林分和19年生中径材培育林分不同间伐处理之间树高、总断面积的差异均不显著。间伐显著增加了林木胸径的生长，大径材培育林分强度和中度间伐处理的平均胸径分别比对照增加13.78%和9.69%，中径材培育林分强度和中度间伐处理的平均胸径分别比对照增加12.28%和7.02%。间伐显著促进了林木单株材积的增加，2组试验林分活立木材积随着间伐强度的增加而降低，第1试验区22年生林分不同间伐强度之间活立木材积的差异不显著（P>0.05），第2试验区强度间伐活立木材积显著低于对照（P<0.05），中度间伐林分活立木材积与对照和强度间伐之间的差异不显著（P>0.05）。2组试验林分总蓄积和出材量也随着间伐强度的增加而降低，二者在3种间伐处理之间均没有显著差异（P>0.05）。间伐强度不能有效增加林分活立木材积和林分出材量，间伐次数对林分出材量及出材规格有重要影响。试验区杉木大径材培育以2次间伐，总间伐强度50%左右较为适宜，而中径材培育则以1次中度间伐（约25%）为宜。

Effect of Thinning on Growth and Timber Outturn in Cunninghamia lanceolata Plantation

Effect of thinning intensity (heavy thinning, moderate thinning and unthinning) and times of thinning (thinning once or twice a rotation) on stand growth and timber outturn of Chinese fir (Cunninghamia lanceolata) were studied in Kaihua, Zhejiang Province. The first experiment was to cultivate big-diameter timber stand and thinned in the seventh year and fourteenth year, respectively, while the second experiment was to cultivate middle-diameter timber stand and thinned in the twelfth year. The results showed that there were no significant difference in tree height and total basal area among three thinning treatments in 22-year-old big-diameter timber stand and 19-year-old middle-diameter timber stand. The diameter at breast height (DBH) increased with the increase of thinning intensity. The average DBH value of big-diameter timber stand with heavy thinning and moderate thinning treatments increased by 13.78% and 9.69%, respectively, compared with the unthinned stand, while the DBH of middle-diameter timber stand with heavy thinning and moderate thinning treatments increased by 12.28 % and 7.02%. Thinning significantly increased the stem volume per tree, the living tree volume (LTV) of stand decreased with the increasing thinning intensity in the two experiments. In the first experiment, there was no significant differences in the LTV of 22-year-old stand among three thinning treatments (P>0.05). In the second experiment, the LTV of 19-year-old stand in the heavy thinning treatment was significantly lower than that in unthinned stand, there was no significant difference in LTV between the moderate thinning treatment and heavy thinning or unthinned treatments (P>0.05). The total stand volume (TSV) and total wood outturn (TWO) reduced with the increasing thinning intensity in the two experiments, there were no significant differences in TSV and TWO among the three thinning treatments (P>0.05). It is concluded that thinning intensity can not effectively increase the live tree volume and timber outturn, and the times of thinning has an important effect on timber outturn and timber size. For big-diameter timber cultivation of Chinese fir, twice thinning with 50% thinning intensity is appropriate in a rotation. It is suitable for middle-diameter timber cultivation with once moderate thinning (approximate 25%).