不同营林措施对马尾松林物种组成及空间结构的短期影响

为揭示常规营林措施对人工马尾松林分物种组成和空间结构的影响，以三峡库区马尾松飞播林为研究对象，按照未采伐、除灌、伐除非马尾松、伐除优势马尾松4种营林措施建立固定监测样地，分析了马尾松林群落的物种组成和数量特征，并运用角尺度、大小比数、混交度3个林分结构参数，研究不同营林措施处理对马尾松林分空间结构的影响。结果表明：不同营林措施对马尾松林物种组成和优势程度存在明显影响，乔木层生物多样性降低，林下灌草层多样性明显提升。除灌对林木空间分布格局未造成显著改变，伐除非马尾松和伐除优势马尾松均提高了林分空间结构的聚集程度，且林木平均聚集程度随着采伐强度增加而增加。不同营林措施对林分整体大小分化程度影响不大，但采伐明显改善了林分的混交程度。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，应根据各树种生物学特性以及功能地位来综合确定采伐木和保留木，并采用中度择伐强度更有利于林分结构调整。

Short-term Effects of Different Forest Management Practices and Spatial Structure of Pinus massoniana Stand

In order to understand the influence of conventional forest management practices on species composition and stand spatial structure of Pinus massoniana forest, P. massoniana plantation with 4 forest management practices in the Three Gorges Reservoir area were taken as the subject (i.e., no cutting; shrubs cutting; non- P. massoniana cutting and dominant P. massoniana cutting) , we analyzed community composition and quantitative features and spatial structure in 3 years post-treatment of each managements type by using 3 structure parameters, which are uniform angle index, neighborhood comparison and mingling intensity. The results show that different forest management practices significantly affect the species composition and degree of advantage species, the biodiversity of arbor layer decreased and that of shrub layer and herb layer increas obviously. Shrubs-cutting measure causes no obvious change on spatial distribution pattern. However, both non- P. massoniana cutting and dominant P. massoniana cutting practices improve the aggregation degree of stand spatial structure, and the average concentration increased as selective cutting intensity improve. Though different practices show no significant effects on neighborhood comparison of P. massoniana, selective cutting obviously improved mingling intensity. Hence, simple regulation on the structure of a species or a single tree level is not conducive to optimize P. massoniana forest stand structure. According to biological characteristics and functional status of tree species, selective cutting tree and maintained tree need to comprehensive determine, and moderate selective cutting intensity is more conducive to forest structural adjustment.