择伐对吉林蛟河阔叶红松林群落结构及动态的影响

科学的森林经营能够优化林分结构,是调控森林生产力和生物多样性的有效手段。择伐作为森林经营的重要方式之一,其对森林结构以及群落动态的影响一直未有定论,因此迫切需要利用更加全面的数据对择伐及伐后林分特征的变化进行长期监测。根据森林大样地建立规范,2010年在吉林蛟河建立了42hm~2阔叶红松林动态监测样地,2011年冬季截取部分面积进行择伐经营,以经营样地为研究对象,运用数值变量描述采伐活动并分析择伐前后群落结构的变化;同时结合2015年的二次调查数据,以立地条件基本一致的对照样地为参照,比较林分水平和物种水平上死亡率、更新率的差异,并利用线性混合效应模型探究择伐活动对个体径向生长的影响。研究结果显示:经营样地的择伐强度为5.4%,受采伐干扰影响较大的物种主要包括色木槭、白牛槭、裂叶榆、胡桃楸、千金榆、水曲柳以及紫椴,采伐主要集中于林冠层树种,亚林层和灌木层个体很少涉及。择伐前后物种组成、径级结构等并未发生明显改变。5年间,经营样地和对照样地的林分密度都降低,对比对照样地,经营样地的死亡率较低,但其更新状况并未优于对照样地。从胸高断面积来看,经营样地整体的年平均生长量高于对照样地,表明择伐导致的稀疏对个体生长和存活起到了一定的促进作用。将采伐强度纳入线性混合效应模型中分析发现,胸径始终是影响个体生长的最重要因素,其次是树木个体之间的非对称竞争;采伐所涉及到的7个主要树种的年平均生长量均高于对照样地,但仅有紫椴的径向生长表现出对采伐干扰的显著响应。综合来看,低强度择伐对群落结构和动态的影响较小,不同物种的径向生长对择伐的响应存在一定差异。

Effects of selective harvest on community structure and dynamics in a mixed broadleaved Korean pine forest in Jiaohe, Jilin Province

Forest management can be used to optimize stand structure, and it is an effective measure to regulate forest productivity and species diversity. The influence of selective harvest, which is an important method of forest management influencing the structure and dynamics of forest stands, does, however, not achieve consistent results. Accordingly, there is an urgent need to use more comprehensive data to study selective harvest and the change in forest stands after harvest. Following the protocols of the Center for Tropical Forest Science forest dynamic plot, we constructed a 42 hm² plot in a mixed broadleaved Korean pine forest, located in Jiaohe, Jilin Province. We selected 19 ha of the plot to manage in the winter of 2011. The study was based on the managed plot, describing the harvest events using simple numeric variables and analyzing the change in the forest structure before and after the harvest event. At the same time, using the data of the second inventory of the plot after 5 years, we compared the mortality and recruitment between the managed plot and the control plot, which had the same habitat conditions at the stand and species levels. A linear mixed-effects model was employed to explore the effects of harvest on the growth of individuals. The results showed that the harvest intensity of the managed plot was 5.4%, as computed by the basal area. The species most influenced by the harvest included Acer mono, Ulmus laciniata, Juglans mandshurica, Carpinus cordata, Fraxinus mandshurica, and Tilia amurensis. Canopy tree species were harvested almost exclusively, whereas only a very few shrubs and sub-canopy trees were harvested. The harvest events did not noticeably change the species composition and diameter at breast height (DBH) distribution. During the 5 years, the stand density was lower than that of 2010 in both plots. The mortality of the managed plot was lower, whereas the recruitment status was not better, than those of the control plot. The basal area increment per year of the managed plot was larger than that of the control plot, indicating that the thinning resulting from harvesting promoted the growth of trees. We entered the predictors representing harvest intensity into the model and found that the DBH was the most significant variable for the growth analysis, followed by the asymmetric competition factor. The predictor representing harvest showed a significant effect only for the growth model of T. amurensis. In general, low harvest intensity had little effect on the structure and dynamics of the community, whereas the radial growth of different species showed various responses to selective harvest.