浑善达克沙地榆树疏林中木本植物空间格局及种内和种间关系分析

Analysis on spatial pattern and intraspecific and interspecific relationships of woody plants in Ulmus pumila-dominated savanna in Otindag Sandy Land

采用相邻网格法对浑善达克沙地榆树(Ulmus pumila Linn.)疏林中的木本植物进行调查;在此基础上,采用点格局分析和成对关联函数g(r)研究不同尺度上单一种类的空间格局以及种类间的空间关联性,并采用完全空间随机零模型和异质性泊松过程零模型对空间格局和空间关联性进行检验。结果表明:该榆树疏林中主要乔木种类为榆树,主要灌木种类为耧斗菜叶绣线菊(Spiraea aquilegifolia Pall.)和小叶锦鸡儿(Caragana microphylla Lam.);其中,成年榆树(DBH≥20cm)和榆树幼苗(无胸径)的数量均较多,但榆树幼树(DBH<5cm)的数量严重不足,甚至缺失,因而,该榆树种群为衰退型种群。点格局分析及零模型检验结果表明:不同龄级榆树以及主要灌木种类在小尺度上呈现显著的聚集分布特征,但聚集尺度存在差异,其中主要灌木种类的聚集尺度更大;且随着空间尺度的增加,聚集程度逐渐下降并表现出随机分布的趋势。不同龄级榆树以及主要灌木种类间的相互作用关系也具有较强的尺度依赖性,不同龄级榆树在小尺度上呈现显著的正向作用关系;榆树分别与耧斗菜叶绣线菊和小叶锦鸡儿在所有尺度(0~50m)上总体呈现相互独立的作用关系,榆树与耧斗菜叶绣线菊和小叶锦鸡儿各自占据不同的空间位置,未产生直接的种间竞争。综合分析结果表明:在浑善达克沙地榆树疏林中,木本植物的空间分布特征明显受生境异质性的影响,未来如果气候干旱加重,榆树的数量可能持续减少,而小叶锦鸡儿等灌木种类的数量则可能持续增加,以榆树为主导的疏林草地类型可能将逐步退化为以灌丛为主导的疏林草地类型。

Woody plants in Ulmus pumila-dominated savanna in Otindag Sandy Land were surveyed by using adjacent grid method;on this basis,spatial pattern of single species and spatial association among species at different scales were researched by using point pattern analysis and paired correlation function g(r),and spatial pattern and spatial association were tested by using complete spatial randomness and heterogeneous poisson process null models.The results show that U.pumila is the main arbor species,and Spiraea aquilegifolia Pall.and Caragana microphylla Lam.are the main shrub species in the U.pumila-dominated savanna;in which,numbers of adult tree(DBH≥20 cm)and seedling(without DBH)of U.pumila are relatively large,but number of sapling(DBH<5 cm)of U.pumila is seriously insufficient,even missing,thus,U.pumila population is a declining one.The results of point pattern analysis and null model test show that U.pumila at different age classes and main shrub species exhibit significant aggregation distribution characteristics at small scale,but there are differences in aggregation scales,in which,the aggregation scale of main shrub species is larger;and with the increase of spatial scale,the aggregation degree gradually decreases and shows the trend of random distribution.The relationships among U.pumila at different age classes and main shrub species also have strong scale dependence,U.pumila at different age classes show a significant positive relationship at small scale;the relationships of U.pumila with S.aquilegifolia and C.microphylla are generally independent at all scales(0-50 m),respectively.U.pumila occupies different spatial positions with S.aquilegifolia and C.microphylla,respectively,and do not produce direct interspecific competition.The comprehensive analysis result shows that in U.pumila-dominated savanna in Otindag Sandy Land,the spatial distribution characteristics of woody plants are obviously affected by habitat heterogeneity,in the future,if the climate drought aggravates,the number of U.pumila may continue to decrease,while the number of shrub species such as C.microphylla,etc.may continue to increase,U.pumila-dominated savanna type may gradually degenerate into shrub-dominated savanna type.