羊草＋大针茅草原退化群落优势种群空间点格局分析

Point pattern analysis of dominant populations in a degraded community in Leymus chinensis + Stipa grandis steppe in Inner Mongolia, China

草原退化的特征主要表现为群落生产力的大幅下降和植物个体的小型化,同时,退化的草原生态系统与一定强度的放牧压力保持平衡而相对稳定。该文应用摄影定位法测定了羊草+大针茅草原退化群落中4个优势种群羊草(Leymus chinen-sis)、米氏冰草(Agropyron michnoi)、大针茅(Stipa grandis)、糙隐子草(Cleistogenes squarrosa)的空间格局。点格局分析结果表明:在空间分布格局上,4个优势种群均偏离完全随机模型和泊松聚块模型,而符合嵌套双聚块模型,也就是说,其空间格局表现为聚集分布,且在大聚块中分布着较高密度的小聚块。严重退化的草原群落中优势种群的嵌套双聚块空间分布格局当属一种集体行为,是种群适应过度放牧压力的一种表现形式,为过度放牧导致的退化草原群落的主要特征之一。这种生态学现象同植物个体小型化一样,是种群易化(正相互作用)的结果。在过度放牧的胁迫下,种群通过改变个体性状及个体在空间的分布状况实现自我帮助,以抵御外界的放牧压力达到自我保护,从而维持退化草原生态系统与放牧压力间的相对平衡。

Aims Steppe dominated by Stipa grandis and Leymus chinensis is the zonal vegetation in the temperate steppe region of China and eastern Eurasia.It has been heavily disturbed by overgrazing in China.Our objective was to investigate the spatial patterns of dominant populations in a degraded community of steppe.Methods We used photography orientation to measure the patterns of dominant populations in a degraded community of typical steppe.We used complete spatial randomness,Poisson cluster process and double-cluster process to analyze the patterns of dominant populations based on point pattern.Important findings The patterns of dominant populations of L.chinensis,Agropyron michnoi,S.grandis and Cleistogenes squarrosa fit the nested double-cluster process at all scales in the community block of 5 m × 5 m.This ecological phenomenon may be induced by facilitation.