间伐对桉树生长及大径材培育的影响

Effects of Thinning on Growth of Eucalyptus for Large-diameter Wood Cultivation

通过对四川乐山7年生桉树人工林不同间伐强度及间伐木保留方式进行研究,分析间伐对桉树单株、林分生长及径阶分布的影响,为四川桉树大径材培养提供依据。结果表明:间伐能显著促进桉树单株的生长,且随时间的推移促进作用更为显著,间伐后3.5年,胸径、树高、单株材积生长量均随保留密度的增大而减小,均以200株·hm^(-2)的低密度单株生长最好,分别比对照高83.76%、33.41%和85.49%。间伐对林分生长量有显著的削弱作用,不同强度间伐的蓄积生长量随保留密度的增大而增大,但均显著低于对照。间伐对枝下高影响不显著,仅在间伐后3.5年对冠幅有显著的促进作用。600株·hm^(-2)均匀保留处理的单株、林分生长量及大径材所占比例均不同程度高于隔行砍行、宽行窄株的保留方式。不同强度间伐大径材所占比例与保留密度成反比。综合分析,以600株·hm^(-2)均匀保留的处理蓄积生长量显著高于低密度林分,单株生长显著高于对照,大径材所占比例大于50%,为四川7年生桉树间伐较好的保留密度。

To investigate the potential for cultivation of large-diameter Eucalyptus in Sichuan,tree volume,stand growth and diameter distributions were examined following different thinning intensities and thinning retention methods in a 7-year-old Eucalyptus plantation in Leshan,Sichuan.The results showed that thinning could significantly promote the growth of Eucalyptus,and the effect was more significant with the passage of time.At 3.5 years after thinning,DBH,tree height and volume growth per tree decreased with increasing retention density.Retention of 200 plants·hm^(-2)provided the best individual tree volume growth,with DBH,tree height and individual tree volume growth of 83.76%,33.41%and 85.49%higher than the control,respectively.However,thinning had a significant weakening effect on stand growth,with volume growth following thinning increasing as retention density increased,but all thinning treatments were significantly lower than the control for volume growth.Thinning had no significant effect on the height to the green crown,but it significantly promoted crown width at 3.5 years after thinning.The growth of individual trees,stand volume and the proportion of large-diameter trees in the uniform retention treatment of 600 plants·hm^(-2) were all higher than that obtained with wide rows and narrow inter-tree spacing in alternate rows.The proportion of large diameter trees thinned at different thinning intensities was found to be inversely proportional to the retention density.Comprehensive analysis showed that the volume growth with 600 plants·hm^(-2) being retained after a uniform thinning treatment was significantly higher than that of lower density forests,and that the growth of individual trees was significantly higher than that of the control while the proportion of large-diameter trees was more than 50%.Thus,thinning 7-year-old trees to retain 600 plants·hm^(-2) proved to be the optimal reserved density for thinning Eucalyptus in Sichuan.