不同生境条件下四合木(Tetraena mongolica Maxim.)种群结构特征

Population structure characteristics of Tetraena mongolica in different habitats

对天然分布区及不同生境内四合木种群的径级结构、年龄结构、冠幅结构、高度结构及空间结构特征进行了比较分析,运用静态生命表描述了四合木种群年龄结构动态变化规律,应用Clark-Evans的R值法计算出四合木个体空间分布格局指标。结果表明:四合木种群径级、龄级与高度级结构均基本呈正态分布,冠幅级结构呈现出近乎指数型的衰减趋势;但不同生境的四合木种群因所处微环境各异,在径级、龄级、高度级、冠幅级结构上表现出一定差异。四合木种群的存活率随龄级的增大而降低,死亡率和消失率随龄级的增大而升高,其存活曲线接近于DeeveyⅠ型,表明该种群为下降种群。不同生境的四合木种群个体分布均不均匀,其空间分布为随机型。

Tetraena mongolica is an endemic and endangered species, and is one of the Chinese national second protective wild plants being listed in the Red Data book. T. mongolica is distributed mainly in Western Ordos Plateau of Inner Mongolia. But for some reasons, the range of the population has been declining. This research was carried out in the natural distribution region and the different habitats of T. mongolica population in order to describe the structure and distribution pattern of the population. 7 plots were established and the field data were collected. Through drawing the charts of diameter-class,age-class, width-class, height-class in different habitats, the comparative analyzing was carried out. The dynamic of age structure of T. mongolica population was concluded according to the static life table, and the population distribution pattern indexes were calculated by using the method of Clark-Evans. The results showed ： （ 1 ） The structures of diameter-class, age-class and height-class of T. mongolica population were in normal-distribution type. The structure of width-class showed approximate exponential decay. The population structure difference among the different habitats Ⅰ was definitely due to the different micro environments. （ 2 ） With the increase of population age-class, the survival rate was decreasing, and the mortality and vanish rate were increasing. The survival curve fitted the Deevey Ⅰ which indicated the population was the descending-type. （3）The individual distribution of T. mongolica populations in different habitats were not even, and the spatial distribution pattern showed in random.