西鄂尔多斯半日花(Helianthemum soongoricum)种群结构和点格局分析

半日花(Helianthemum soongoricum)是古地中海区系的残遗种,是国家二级珍稀保护植物,种群数量和规模已非常有限。为了揭示半日花种群的结构和发展的空间规律,运用大小结构分析法将半日花种群分为3个龄级(Ⅰ级,d≤3cm;Ⅱ级,3cmd≤9cm;Ⅲ级,d9cm,d为植株体积(高度×冠幅)的立方根),并采用空间点格局分析中的O-ring统计方法研究了分布于西鄂尔多斯砾石质和石质生境的半日花种群的结构和不同发育阶段个体的空间格局及空间关联性。结果表明:(1)半日花个体主要集中在龄级Ⅱ,龄级Ⅰ和龄级Ⅲ的个体都较少,种群的更新受到限制;(2)半日花种群的空间分布格局与不同龄级间的空间关联性受生境条件的影响较大,并且对空间尺度表现出很强的依赖性。砾石质生境中的半日花种群及其各龄级在小尺度范围内呈聚集分布,随着尺度增大逐渐趋向于均匀分布,不同龄级间主要表现为(或接近于)负关联;石质生境中半日花种群及其各龄级在中小尺度呈聚集分布,随着尺度增加表现为随机分布,龄级Ⅲ与Ⅱ和龄级Ⅱ与Ⅰ之间的空间正关联或不关联关系更明显。这种差别与两种生境下的环境条件和群落结构有关;(3)半日花幼龄个体(龄级Ⅰ)在一定程度上受到了来自成年个体(龄级Ⅱ与Ⅲ)的竞争压力。研究结果对半日花的保护与利用具有一定的参考价值。

Population Structure and Spatial Point Pattern of Helianthemum soongoricum in West Ordos,Inner Mongolia,China

Helianthemum soongoricum is a tertiary relic plant and now is listed as secondary rare and endangered plant of China with limited population size. To explore the population structure and spatial distribution pattern, size classes statistics and the pair correlation function, O-ring statistic of the point pattern analysis, was used to analyze the population structure, spatial pattern and spatial associations of individuals in different development stages of H. soongoricum living in two habitats respectively. The results showed that, (1) Majority of H. soongoricum individuals were in age class Ⅱ(3 cm9 cm) were less, so the regeneration of H. soongoricum population was limited. (2) The spatial pattern and spatial associations between different age class individuals of H. soongoricum population were affected by habitat environment and depended on spatial scale strongly. In gravel habitat, H. soongoricum population and the individuals in each age class were clumped at small scales, and then tended to be uniform distribution with the increase of spatial scale. The spatial associations between different age class individuals were found to be or close to negative association. In stony habitat, H. soongoricum population and the individuals in each age class showed aggregated distribution at small and middle scales, and random distribution at larger scale. There were positive association between age class Ⅲ and Ⅱ, and no significant association between age class Ⅱ and Ⅰ. These differences between two habitats were resulted from their environmental conditions and plant community structures. (3) The young H. soongoricum individuals suffered competition pressure form the adult individuals to some extent. Our results have certain reference value for the protection and use of H. soongoricum.