Using Levins' niche breadth,Whittaker's niche similarity and Pianka's niche overlap,13 tree species in Stewartia shensiensis Chang community were surveyed and estimated.The results showed that:the niche breadth of the main dominant populations in Stewartia shensiensis Chang community was large.The niche breadth of Stewartia shensiensis Chang and co-dominant species Carpinus cordata Bl,Acer tegmentosum Maxim and Quercus aliena var.acuteserrata Maxim were 1.730 1,1.760 6,1.780 8 and 1.734 9,respectively.The Stewartia shensiensis Chang had a higher niche similarity with its co-dominant species.There is no significant correlation between niche breadth and niche similarity.The species with broad niche breadth had a larger niche overlap with other species due to its strong resource utilization ability,wide distribution and more competitive.Mmeanwhile,the species with narrow niche breadth could be difficult to coexistence with other populations due to its weak resource utilization ability,narrow distribution and weak competitive.The niche overlap was not necessarily high among populations with large niche breadth.According to niche overlap,the competition between Stewartia shensiensis Chang and understory species was greater than that between co-dominant story species.%利用Levins生态位宽度、Whittaker生态位相似度和Pianka生态位重叠等公式测算了宝天曼陕西紫茎群落13种主要乔木树种的生态位宽度、生态位相似性和生态位重叠.结果表明,陕西紫茎群落中主要优势种群的生态位宽度较大,陕西紫茎与其共优种青楷槭、千金榆、锐齿栎的生态位宽度分别是1.730 1、1.7606、1.780 8、1.734 9,且与共优种的生态位相似性较高,生态位宽度与生态位相似性之间无明显的关联性;生态位宽度较大的物种因其对资源的利用能力较强、分布较广、有较大竞争力而与其他种群间的生态位重叠较大,生态位宽度较小的物种由于对资源的利用能力较弱、分布不够广泛、竞争力弱而有可能导致与其他种群难以共存,具有较大生态位宽度的种群之间的生态位重叠并不一定较高.从陕西紫茎群落生态位重叠值来看,陕西紫茎与林下层种群的竞争要大于其对共优层种群的竞争.
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