在实地踏查的基础上，对宁夏六盘山20个毛榛（Corylus mandshurica Maxim.）群落乔木层、灌木层和草本层的物种组成进行了调查，在此基础上，对灌木层优势种（重要值在1.5%以上）的重要值、生态位宽度（Levins指数和Shannon-Wiener指数）和Pianka生态位重叠指数进行了分析，并采用方差比率、χ²检验、Pearson相关系数、Spearman秩相关系数和联结系数分析灌木层优势种的种间联结性。结果表明：该群落乔木层、灌木层和草本层植物分别有15科29属46种、26科42属80种和36科57属70种；灌木层中20种植物的重要值在1.5%以上，且这些种类的重要值和2个生态位宽度指数的排序结果基本一致，其中，毛榛的重要值（7.21%）、Levins指数（0.71）和Shannon-Wiener指数（4.10）均明显大于其他优势种。在灌木层优势种组成的190个种对中，多数种对的Pianka生态位重叠指数小于0.5；毛榛与甘肃山楂（Crataegus kansuensis Wils.）、紫丁香（Syringa oblata Lindl.）和鞘柄菝葜（Smilax stans Maxim.）等8个优势种的Pianka生态位重叠指数在0.5以上。总体联结性分析结果（方差比率为1.16，统计量为92.95）表明：该毛榛群落灌木层优势种的总体联结性为不显著正联结。χ²检验结果显示：正联结种对有110个，负联结种对有80个，其中，联结性达到极显著和显著水平的种对分别有6和11个，二者占比不足10%。Pearson相关系数、Spearman秩相关系数和联结系数的结果与χ²检验结果相同，均以不显著联结的种对为主，毛榛与多数优势种的联结性不显著，仅与个别优势种（如鞘柄菝葜）的联结性显著。综合分析认为，宁夏六盘山毛榛群落灌木层物种较为丰富，灌木层优势种的种间联结性较弱，各种类间相对较为独立。

Species composition of arbor layer, shrub layer, and herb layer of 20 Corylus mandshurica Maxim. communities in Liupan Mountain of Ningxia were investigated based on field investigation. On the basis, the importance value, niche breadth (Levins index and Shannon-Wiener index), and Pianka niche overlap index of dominant species (importance value greater than 1.5%) in shrub layer were analyzed, and the interspecific associations among dominant species in shrub layer were analyzed by using variance ratio, χ² test, Pearson correlation coefficient, Spearman rank correlation coefficient, and association coefficient. The results show that there are 46 species in 29 genera of 15 families, 80 species in 42 genera of 26 families, and 70 species in 57 genera of 36 families in arbor layer, shrub layer, and herb layer of the community, respectively; there are 20 species with the importance values greater than 1.5% in shrub layer, and the ranking results of importance values of these species are basically consistent with those of two niche breadth indexes, in which, the importance value (7.21%), Levins index (0.71), and Shannon-Wiener index (4.10) of C. mandshurica are all evidently greater than the other dominant species. Among 190 species pairs composed of dominant species in shrub layer, the Pianka niche overlap indexes of most species pairs are smaller than 0.5; the Pianka niche overlap indexes of C. mandshurica with eight dominant species such as Crataegus kansuensis Wils., Syringa oblata Lindl., Smilax stans Maxim. and so on are greater than 0.5. The overall association analysis result (the variance ratio is 1.16 and the statistics is 92.95) shows that the overall association of dominant species in shrub layer of the C. mandshurica community is nonsignificant positive association. The χ² test result shows that there are 110 positively associated species pairs and 80 negatively associated species pairs, in which, the associations of 6 and 11 species pairs reach extremely significant and significant levels, respectively, and their percentage is lower than 10%. The results of Pearson correlation coefficient, Spearman rank correlation coefficient, and association coefficient are the same as the result of χ² test, which are dominated by species pairs with no significant association. The associations of C. mandshurica with most dominant species are not significant, and C. mandshurica only has significant associations with a few dominant species (such as S. stans). It is suggested that the species in shrub layer of C. mandshurica community in Liupan Mountain of Ningxia are relatively abundant, the interspecific associations among dominant species in shrub layer are relatively weak, and each species is relatively independent.