沙埋对西鄂尔多斯高原灌木群落格局的影响

Impact of sand burial on spatial patterns of shrub communities on the western Ordos Plateau,northwestern China

西鄂尔多斯高原集中分布了很多珍稀濒危灌木物种,近年来遭遇了不同程度的沙埋,为了揭示沙埋对该区灌木群落的影响,采用2006年西鄂尔多斯高原干旱荒漠灌木群落的空间点格局调查数据,运用基于最近邻体距离的空间格局指数F函数、G函数和J函数,研究了不同沙埋程度干扰下灌木群落的结构和空间格局。结果表明:沙埋是该区不耐沙灌木消亡的重要影响因素,随地表覆沙厚度的增加,群落内不耐沙灌木的数量逐渐减少;对于耐沙灌木,浅层的覆沙有利于其更新生长,而当覆沙厚度超过一定值时,这种正向作用转为负向作用,导致耐沙灌木由数量上的增加转为减少;不耐沙灌木和耐沙灌木在不同沙埋强度的影响下,在小尺度上都表现为显著的随机分布,而二者之间在浅层的沙埋干扰下,在小尺度上有较显著的负相关关系,当覆沙厚度达12cm时,群落内灌木分布极稀疏,也没有显著的相关关系。沙埋导致群落内物种单一且有老龄化现象,更新困难,是群落退化的重要驱动力。

The western Ordos Plateau is a distribution center of many endangered shrub species,which have suffered sand burial to various degrees during the last few years.According to the survey data of spatial point pattern of shrub communities in the arid desert of western Ordos Plateau in 2006,we investigated the structure and spatial pattern of shrub communities under different levels of sand burial to reveal its effects on shrub communities in this area.Three indices of spatial pattern based on the nearest neighbor distance,i.e.the F（t）,G（t） and J（t） functions,were selected.The results indicate that sand burial is an important factor causing the extinction of sand intolerant shrubs.The number of sand intolerant shrubs gradually reduced with an increase in the depth of sand burial.For sand tolerant shrubs,shallow sand burial promoted their germination and growth,but this positive role changed to a negative effect when the depth of sand burial exceeded a specific value,showing at first an increase in the number of sand tolerant shrubs and then a decrease.Both sand tolerant and intolerant shrubs showed a random distribution pattern on a small scale under various levels of sand burial,with a significantly negative correlation under shallow sand burial.When the depth of sand burial exceeded 12 cm,the shrubs appeared to be sparsely distributed and without any significant correlation.Sand burial is an important driving force in community degradation,which tends to cause the singleness and aging of shrub species in the community and difficulty to regenerate.