抚育择伐对马尾松林主要树种空间分布格局及其关联性的短期影响

探讨不同抚育择伐方式下森林群落物种空间分布格局和关联性,对科学优化森林结构和促进森林稳定发展具有重要意义。以三峡库区马尾松飞播林为研究对象,采用未择伐、伐除优势马尾松、伐除非马尾松、除灌等处理方式建立固定监测样地,利用Ripley′s L函数的空间点格局方法,分析抚育择伐3年后马尾松林的群落组成、空间分布格局、种间关联性的变化特征。结果表明:1)不同抚育择伐措施均在一定程度上改变了物种组成以及部分树种的优势程度,降低了各样地乔木层物种多样性。2)未择伐主要树种空间分布格局以随机分布为主,伐除优势马尾松样地优势树种主要呈现聚集分布,伐除非马尾松改变了香椿和盐肤木等树种的分布格局,呈聚集分布,其他优势树种空间分布格局与对照样地相似;除灌进一步加剧林下更新树种的随机分布。3)未择伐样地主要树种空间关联性表现为正相关或不相关,伐除优势马尾松增加了主要树种间的负相关性,伐除非马尾松和除灌措施则增加了种间的不相关性。短期人为择伐干扰明显改变了林分空间结构和稳定性,择伐对象不同对林分结构产生的影响也不同。单纯调整某个树种或单个层次的结构来开展森林经营,不利于林分空间结构的整体优化,必须要综合考虑择伐强度和择伐对象的选择,将有助于实现森林结构优化和功能提升。

Short-term effects of selective cutting on the spatial distribution and association of dominant tree species in Pinus massoniana stands

Selective cutting is an important method utilized in forest management and tends to change the species composition and structure of forest stands. Examining the impacts of various selective cutting methods on the spatial distribution pattern and associations of dominant tree species in forest community is important to optimize the forest structure and promote forest stability. In the present study, Pinus massoniana air seeded plantation in the Three Gorges Reservoir Area were selected, using non-cutting, P. massoniana-cutting, non P. massoniana-cutting, shrubs-cutting methods, the community composition, spatial distribution pattern and the interspecific association among the dominant tree species were evaluated. Ripley''s L function method of spatial point pattern was used to analyze the variations of the characteristics for over 3 years in different selective cutting plots. The results showed that, all the selective cutting methods altered the species composition, the advantage degree of some of the tree species and reduced the arbor tree species diversity in all the plots. The dominant tree species in the non-cutting plot represented the random distribution, whereras represented an aggregated distribution in P. massoniana-cutting plots. Non P. massoniana-cutting methods made changes of the spatial distribution of Toona sinensis and Betula luminifera and formed aggregated distributions for the two species, while other species had no significant changes of the spatial distribution compared with the control plots. Shrubs-cutting methods strengthened the random distribution of regenerated tree species. Positive and non-interspecific spatial associations of the dominant tree species were found in the controlled cutting plots. P. massoniana-cutting plots increased the negative interspecific associations, while non P. massoniana-cutting and shrubs-cutting methods increased the non-interspecific associations. Short-term selective cutting interferences apparently altered the structure and stability of the forest stands, and which more largely depends on the target cutting species. Adjusting a specific species or the structure of a specific layer is not conducive for optimizing the P. massoniana forest spacial structure during the forest management. Comprehensively consideration of selective cutting intensity and target cutting species would be beneficial for achieving structure optimization and function improvement.