典型草原退化群落不同恢复演替阶段羊草种群空间格局的比较

CHANGES IN THE POPULATION SPATIAL DISTRIBUTION PATTERN OF LEYMUS CHINENSIS IN DEGRADED STEPPE COMMUNITY DURING RESTORATIVE SUCCESSION IN INNER MONGOLIA,CHINA

羊草(Leymus chinensis)为典型草原群落的主要建群种之一,在群落中扮演着重要角色。应用摄影定位法测定处于不同恢复演替阶段的羊草种群空间格局,通过点格局、种群空斑、种群领地及种群领地密度等方法分析发现,羊草种群在恢复演替过程中经历了种群增长和种群衰退的过程。在此过程中,羊草种群数量出现最高点,此点之前,种群拓殖大于自疏,种群整体增长;此点之后,种间竞争及种内竞争致使种群衰退,而种间竞争占主导地位,种内竞争相对较弱。羊草种群的增衰导致种群空斑发生变化,从而引起种群格局类型发生相应的变化,表现为在恢复21a的群落中,羊草种群在10m×10m的取样范围内表现出两种格局分布类型:在0～4.85m之间呈现聚集分布,当尺度大于4.85m时,则表现为随机分布;在恢复8a的群落中,羊草种群在10m×10m的取样范围内出现3种格局分布类型:在0～3.01m之间呈聚集分布,在3.01～3.37m之间为随机分布,当尺度大于3.37m时则表现为均匀分布;在严重退化群落中,羊草种群在整个10m×10m测定尺度上呈现聚集分布。由此可见,羊草种群格局在恢复演替过程中是变化的,这种变化主要由群落剩余资源驱动下的种群拓殖及种内种间竞争所致。

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 pattern of L. chinensis in a degraded community of steppe during restorative succession. Methods We studied three fenced plots of degraded steppe in the Xilin Gole League, Inner Mongolia, China, which had been monitored by the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. We applied a new method of photography to measure the population pattern of L. chinensis, analyzing the point pattern, the area of ＂hole＂, population territory area and territory density in different restorative succession stages. Important findings During the process of restorative succession, the L. chinensis population increased, decreased and became stable. The population originally increased because colonization exceeded self-thinning. The decrease resulted primarily from interspecific competition and secondarily from intraspecific competition. The change of the hole was the result of the increase and decrease of L. chinensis, which led to the change of the pattern type. The distribution of Leymus chinensis was clumped at 0-4.85 m and random at 4.85-10 m in the sample plot fenced-off since 1983. It was clumped at 0-3.01 m, random at 3.01-3.37 m and regular at 3.37-10 m in the sample plot fenced-off since 1996. But it was clumped at 0-10 m in the seriously degraded community.