中文摘要：

采用样方法对陕西周至老县城自然保护区森林植物群落进行调查，运用生态位宽度（B）、生态位重叠值（L）及生态位相似比例（c）指标对主要乔木种群的生态位特征进行测定与分析，探讨植物种群在群落中的地位和作用以及彼此间的竞争关系。结果表明：（1）经调查老县城自然保护区共记录到植物物种243种，隶属于64科159属；分为3个植被型、9个群系。（2）主要乔木种群中，华山松和锐齿槲栎的生态位宽度较大，其Bi、Ba值分别为0．654、0．699和0．534、0．460；短柄袍栎和兴山榆的生态位宽度较小，其Bi、Bn值分别为0．064、0．023和0．049、0．016。（3）自桦和太白杨、糙皮桦和山杨种对的生态位重叠值和生态位相似性比例均较大，其Lji Lji分别为0．108、0．114和0．089、0．128，C。分别为0．939和0．744。优势种间的生态位重叠值和生态位相似比例总体较小，表明在现阶段群落演替中，植物对环境资源的竞争不激烈，物种空间异质性低。

英文摘要：

A field plot sampling method was employed to investigate communities of natural forests in Zhouzhi Laoxiancheng Natural Reserve of Shaanxi. Parameters of niche breadth （B）, niche similarity （L） and niche overlap （C） were calculated to analyze community characteristics. The results showed that： （1） 243 species were recorded and they belong to 159 genera and 64 families. The plots were classified into 3 vegetation types and 9 formations. （2）Niche breadths of Pinus armandii and Quercus aliena var. acutiser- rata were larger than other species in main tree populations,with Levins （Bi） and Hurlbert＇s （Be） values being 0. 654 and 0. 699,and 0. 534 and 0. 460 respectively; Smaller niche breadths were found in Quercus serrata var. brevipetiolata and Ulrnus bergmanniana species, with Bi and Ba values being 0. 064 and 0. 023, and 0. 049 and 0. 016 respectively. （3）The species pairs which have higher niche similarity and niche over- lap were Betula platyphylla and Populus purdomii, Populus davidiana and Betula utilis, with L0 and Lji values being 0. 108 and 0. ll4,and 0. 089 and 0. 128,Cii values being 0. 939 and 0. 744,respectively. The lower niche similarity and niche overlap among dominant species means less fierce interspecies competition and low spatial heterogeneity at current stage in the community succession.