抚育间伐对小兴安岭天然次生林中云杉、冷杉的碳密度分配与竞争的影响

间伐改变林分环境，也对林木生长、森林碳储量及林木竞争关系造成一定影响，研究15%、25%、35% 3个间伐强度处理8 a后小兴安岭天然次生林中杉木的径阶分布、碳密度分配特征及竞争指数，对森林经营的指导和森林碳汇发展有重要意义。结果表明，35%抚育间伐强度均使杉木径阶分布频率偏离正态性；间伐改变了林木各器官碳密度的分配，其趋势是随着间伐强度的增大树干碳密度占总量的比例先减小再增加，而树枝生物量分配规律则呈逐渐减小的趋势；25%和35%间伐强度，杉木地上部分的生物量和碳密度均显著大于对照样地，其中25%间伐强度时生物量和碳密度最大，而15%间伐强度的杉木生物量与对照样地无显著差异，而碳密度却小于对照样地；同CK相比，T₁₅样地杉木的Hegyi竞争指数减少了2.05%，而T₂₅、T₃₅分别增加了36.07%和14.66%；冗余分析（RDA）结果表明，Hegyi竞争指数、间伐强度共同解释了碳密度变化的61.3%，且Hegyi竞争指数增长不利于林分碳密度增加，竞争压力通过改变各器官的碳密度来响应。

Effects of Tending Thinning Intensity on the Carbon Density Distribution Characteristics of Natural Forest

The forest management of thinning can change the forest stand environment,it exhibits a certain impact on tree growth,forest carbon storage,and forest competition.In this study,the diameter rank distribution,carbon distribution,and competition index of the fir stands occurring in the natural secondary forests in the Xiaoxing'an Mountains,which were thinned with the densities of 15%(T₁₅),25%(T₂₅),and 35%(T₃₅)were investigated after 8 years of thinning management.The results showed that T₃₅ intensity made the distribution frequency of fir diameter steps deviated from normality;thinning management changed the distribution of the carbon density of the various organs of the tree,and the proportion of the trunk carbon density to the total increased first and then decreased with the increase of thinning intensity,while the proportion of the branch biomass gradually decreased.The biomass and carbon density of the above-ground part with the densities of T₂₅ and T₃₅ were significantly higher than those of the control plot,and T₂₅ was found the highest biomass and carbon density;no significant differences in biomass were observed between T₁₅ and the control,while the carbon density of T₁₅ was less than the control.Compared with the control,the Hegyi competition index of T₁₅ decreased by 2.05%,while those of T₂₅ and T₃₅ increased by 36.07%and 14.66%,respectively.Redundant analysis indicated that the Hegyi competition index and thinning intensity jointly explained 61.3%of the carbon density change,and the increase of the Hegyi competition index was not conducive to the forest carbon density,the competitive pressure responded by changing the carbon density of each organ.