珍稀濒危植物长蕊木兰种群的年龄结构与空间分布

Age structure and spatial distribution of the rare and endangered plant Alcimandra cathcartii

珍稀濒危植物长蕊木兰为国家Ⅰ级保护植物。然而,由于受研究尺度和分析方法的限制,对其种群生态特征等方面仍不清楚。以云南高黎贡山原生的中山湿性常绿阔叶林4 hm2样地调查数据为基础,应用Ripley的L函数分析了长蕊木兰种群的年龄结构与空间分布格局。研究发现:(1)长蕊木兰种群的年龄结构为反"J"型,属稳定型种群。(2)长蕊木兰种群个体的空间分布格局与空间尺度关系密切,空间尺度小于75 m时为聚集分布,大于75 m时为随机分布。生境异质性在长蕊木兰种群空间分布格局的形成中可能发挥了重要的作用。(3)不同发育阶段个体的空间分布格局存在明显的差异,中树和小树阶段的分布格局在中、小尺度上呈聚集分布,在较大尺度上呈随机分布;大树阶段在整个空间尺度上均呈现随机分布。(4)长蕊木兰不同发育阶段的空间关联性主要表现为中、小尺度上的负相关,在较大尺度上则趋向于无关联。

Understanding the population′s change patterns in time and space of endangered species is essential for decision-making to conservation of the rare and endangered species.However,most populations of these species are small,and it is difficult to use traditional quadrat sampling techniques for demographic analysis.Alcimandra cathcartii,a rare and endangered plant,is one of the first-class nationally protected species in China,but little is known about the population ecology of this species because of the limitations of research scale and analytic methods.The objective of this present study is to examine： 1） the age structure of A.cathcartii population;2） spatial distribution pattern and its change with spatial scale;and 3） the spatial distribution pattern and spatial relationship at different spatial scales and growth stages.The Ripley′s L-function was used to analyze the spatial pattern and spatial association of different development stages,based on the investigation data from 4-hm2 plot in a primary middle-mountain moist evergreen broad-leaved forest in Gaoligong Mountain,Yunnan.The 4-hm2 plot was divided into 100 quadrats,and all stems of A.cathcartii with diameter at breast height（DBH） ≥1 cm were measured,tagged,and mapped.All individuals of this species were divided into three growth stages according to its DBH sizes： small trees,1 cm≤DBH〈7.5 cm;medium trees,7.5 cm≤DBH〈22.5 cm;and large trees,DBH≥22.5 cm.The results showed that the number of small individuals of A.cathcartii was the highest in three growth stages.The age structure of the species was inverted ＂J＂ shape curve,and the population is currently in rising stage and is stable.The distribution pattern of this population is closely related to the spatial scale,with an aggregation distribution in less than 75 m and a random distribution in ≥75 m spatial scale.The habitat heterogeneity may play an important role in the formation of the spatial distribution of the population.There were obvious differences in spatial distribution patterns among different growth stages of the population.The smaller individuals showed aggregation distribution at smaller spatial scale,while larger trees were random distribution type at all spatial scales（0—100m）.The spatial relationships among different development stages are negative correlation at smaller scale,while it tends to be no association at larger scale.This indicates that there may be different mechanism on the formation of distributions at different spatial scales and growth stages.Based on the analysis,it was suggested that the age structure and spatial distribution pattern of A.cathcartii population were determined by the combined impact of the species bioecological properties,intra-and inter-specific interactions,and environmental factors.The results of this study implicates that it is important for conservation of small populations of A.cathcartii to strengthen protection of the forest ecosystem and habitats with these rare and endangered species.