天目山常绿落叶阔叶林群落垂直结构与群落整体物种多样性的关系

Abstract

以浙江省天目山1 hm²常绿落叶阔叶混交林样地调查数据为基础，运用K-means聚类方法将DBH≥1 cm的个体根据树高划分为不同林层，研究比较了各个林层的物种多样性特点；利用通径分析方法和决策系数定量计算各个林层物种多样性对群落整体物种多样性的直接作用和间接作用，天目山常绿落叶阔叶林垂直结构对群落物种多样性构成的影响。结果表明：（1）天目山常绿落叶阔叶林群落层次结构丰富，树高由1.4-36.5 m依次可分为灌木层、亚冠层、林冠下层、林冠中层和林冠上层。（2）天目山常绿落叶阔叶林群落从灌木层依次往向上，物种丰富度、多度、特有种数量、Shannon-Weiner指数和Simpson指数均呈下降趋势。（3）灌木层对群落物种多样性的贡献最大且远高于其他四个林层，其中灌木层对群落整体物种多样性Shannon-Wiener指数、Pielou指数以及Simpson指数的决策系数分别为0.850、0.651、0.755。（4）林冠下层、林冠中层和林冠上层密度的大小对灌木层的物种数目有明显的影响，林冠层密度越大，灌木层群落的物种数目越少，复杂程度越低；偶见种和稀有种对群落物种多样性的维持具有特殊作用。综上，研究认为森林群落的垂直结构在维持森林群落整体物种多样性中具有关键作用，而灌木层在群落整体物种多样性构成中具有决定作用，森林群落中稀有种、偶见种多少在群落物种多样性构成中具有特殊作用。;Based on the survey data of 1 hm² deciduous and evergreen broadleaved forest plot in Tianmu Mountain of Zhejiang Province, we assessed species biodiversity by K-means clustering method, the individuals with diameter at breast height(DBH) ≥ 1 cm was divided into different forest layers according to tree height, and the features of species diversity in each layer were computed, compared, and contrasted. In addition, the direct and indirect biodiversity impacts also evaluated by using path analysis, namely, the quantity of decision coefficients. The objective of the study was to reveal the influence of vertical structure on community species diversity in an evergreen deciduous broad-leaved forest community. The results demonstrated that:(1) the forest community had multiple-layered vertical structure, which could be divided into five layers:shrub layer (1.4-4.2 m), sub-canopy layer (4.3-7.6 m), lower canopy layer (7.7-13.4 m), middle canopy layer (13.5-21.5 m), and upper canopy layer (21.6-36.5 m). (2)The species richness,abundance,the number of endemic species, Shannon-Weiner index and Simpson index of the community appeared a downward trend from bottom to top layers. (3)Shrub layer was the largest contributors to the community overall species diversity index and was much higher than the other four forest layers. And the decision coefficient of shrub layer towards overall species diversity of community that Shannon-Wiener index, Pielou index and Simpson index was 0.850, 0.651, and 0.775, respectively. (4) The density of lower canopy, middle canopy, upper canopy had a negative impact on the species number of the shrub layer. The larger density of the forest canopy was, the less the number of species would become in the shrub community as well as the complexity. In addition, the occasional and rare species in the shrub layer also played a key role in maintaining the species diversity of the shrub layer. In conclusion, the vertical structure of the community was critical in maintaining the overall species diversity of the given forest community. The shrub layer played a decisive role in the composition of overall species diversity, besides the number of occasional and rare species also played a key role on the composition, thus, species diversity of the community.