濒危植物大果木莲种群格局及濒危原因分析

采用径级结构代替年龄结构以及方差均值比率法对木兰科(Magnoliaceae)木莲属(Manglietia Bl.)濒危植物大果木莲(Manglietia grandis Hu et Cheng)种群的年龄结构和种群格局进行了研究,并编制了大果木莲种群的特定时间生命表和存活曲线;结合生殖生物学特征以及遗传多样性研究结果,分析了导致大果木莲濒危的主要原因.根据株高和胸径可分别将大果木莲种群的年龄结构分为5级、高度结构分为6级;在大果木莲的5个年龄结构分级中,成年个体较多,幼年个体较少;其高度结构完整,个体高度主要在20 m以下.种群的方差均值比率为0.838 3,其空间分布格局属于随机分布.根据特定时间生命表可将大果木莲种群的发育分为3个阶段:幼树阶段(年龄级为Ⅱ～Ⅲ级)、成树阶段(年龄级为Ⅲ～Ⅳ级)、老树阶段(年龄级为Ⅳ～Ⅴ级),其中成树阶段个体死亡率最低.大果木莲种群存活曲线接近Deevey Ⅰ型,属于衰退型种群.种群自我更新能力差、种子生产力低下、有性生殖困难、生境片断化导致的基因流受限以及人为干扰是大果木莲濒危的主要原因.针对大果木莲濒危现状和致危原因,提出了相应的保护对策和建议.

Analyses on population pattern and endangered causes of endangered species Manglietia grandis Hu et Cheng

Using the way of diameter structure instead of age structure and variance/mean ratio method,the age structure and population pattern of the endangered species Manglietia grandis Hu et Cheng belonging to Manglietia Bl.in Magnoliaceae were studied,and the time-specific life table and survival curve of the species was created.And combining with research results of propagation and genetic diversity,the main endangered causes were analyzed.According to tree height and diameter of breath height,age structure of M.grandis population is divided into five classes and its height structure into six classes.There are more adults and less young trees in five age classes.The height structure of M.grandis population is complete and tree height is mainly below 20 m.The population pattern is characterized by a random distribution with S2/M=0.838 3.According to the time-specific life table,the development process of M.grandis population can be divided into three stages: sapling stage(Ⅱ-Ⅲ age class),mature tree stage(Ⅲ-Ⅳ age class) and old tree stage(Ⅳ-Ⅴ age class),with the lowest mortality rate in mature tree stage.The survival curve of M.grandis is close to Deevey Ⅰ type,meaning M.grandis population belongs to declined type.It is suggested that lacking regeneration,low seed production capability,sexual reproduction difficulty,limited gene flow caused by habitat fragmentation and intensive human activity are main endangered causes of M.grandis.Aiming to endangered situation and causes of M.grandis,the conservation strategies and proposals are put forward.