林分因子对张北杨树人工林林下草本层物种多样性的影响

The influence of stand factors on species diversity of herb layer in Zhangbei poplar plantations

研究人工林林分因子对林下草本层物种多样性的影响,对于人工林的抚育及合理经营有着重要意义。本研究调查了张北杨树人工林的林分死亡率、平均树高、平均枝下高、平均胸径、平均冠幅及林分密度等6个林分因子及林下草本层的群落特征,并计算出物种多样性指数,探究张北杨树人工林林分结构和林下物种多样性随林分因子的变化特征。结果表明:研究区林下草本层共发现维管植物44种,隶属于17科38属,其中以菊科(Compositae)、豆科(Leguminosae)、禾本科(Gramineae)植物最多;林下草本层物种水分生态类型主要以旱生类植物为主,合计25种,占总种数的56.82%,植物生活型谱中以地面芽植物为主,共27种,占总种数61.36%;物种丰富度指数、Shannon指数和Pielou均匀度指数在各样地内存在显著差异,且物种丰富度指数变异系数最大,Simpson指数在各样地之间不存在显著差异,变异系数最小;各样地之间的林分因子均存在显著差异,其中林分死亡率的变异程度最高,平均胸径的变异程度最低;影响林下草本层物种丰富度指数的主要林分因子有林分死亡率、平均枝下高、平均胸径和林分密度,影响Shannon指数的主要林分因子有林分死亡率、平均树高、平均胸径和林分密度,各林分因子对Simpson指数和Pielou均匀度指数的影响均无显著差异。适当调控林分密度,保持树种针阔混交,将有利于张北杨树人工林林下草本物种多样性的维持。

Understanding the influence of stand factors on species diversity of herb layer in forest plantations is of great significance for forest tending and rational management. In this study,we investigated six stand factors（ i.e.,stand death rate,average tree height,average branch height,average diameter at breast height,average crown width,and stand density） and community characteristics of herb layer in Zhangbei poplar plantations. The species diversity indices of herb layer were calculated to analyze the changes in stand structure and species diversity of herb layer with changes of stand factors. The results showed that 44 species of vascular plants in herb layer were found,belonging to 38 genera of 17 families. The top three families with the most species were Compositae,Leguminosae and Gramineae. Xerophytes were the dominant ecological water type of plants,with a total of 25 species accounting for 56.82% of all species. Hemicryptophyte,a total of 27 species,was the dominant life form in herb layer,which accounted for 61.36% of the total species. The species richness index,Shannon index and Pielou index varied among different plots,with species richness index having the largest coefficient of variation（ CV）. Simpson index did not vary among different plots,with a minimal CV. There were significant differences in the stand factors among various plots,among which the degree of variation of stand death rate was the highest,and the variation degree of average diameter at breast height was the lowest. The main stand factors affecting species richness index of herb layer were stand death rate,average branch height,average diameter at breast height and stand density. The main stand factors affecting the Shannon index were stand death rate,average tree height,average diameter at breast height and stand density. Stand factors had no effects on Simpson index and Pielou index. Appropriate regulation of stand density and mixture of poplar with conifer species would be beneficial to the maintenance of species diversity of herb layer in Zhangbei poplar plantations.