毛乌素沙地油蒿种群点格局分析

 油蒿(Artemisia ordosica)是我国北方农牧交错带的重要固沙植物，研究其种群格局对理解种群生态过程和改善流沙治理技术具有重要意义。点格局分析法是20世纪末发展起来的多尺度空间格局分析方法。通过研究油蒿种群的点格局，发现油蒿种群的空间分布格局和空间关联性同空间尺度、植株形体大小以及生境3种因素有密切联系。在较小的空间尺度上，油蒿种群倾向于非随机分布(集群分布比均匀分布常见)，个体间有较强的空间关联(正关联比负关联常见)；当空间尺度大于临界值后，油蒿种群倾向于服从随机分布，同时种群的空间关联性减弱。幼小油蒿植株具有明显的集群分布趋势，高大植株则表现出聚集强度的降低趋势；形体大小的差异越大，植株间的正关联关系越弱，或者负关联关系越强。与固定沙地相比，半固定沙地油蒿种群的集群分布现象更加明显，同时种群的空间正关联关系更强。研究结果表明，当通过移栽油蒿成体治理流动沙地时，应尽量将其栽种成集群分布而非均匀分布的形式，以提高植株成活率。

POINT PATTERN ANALYSIS OF ARTEMISIA ORDOSICA POPULATION IN THE MU US SANDY LAND

Background and Aims Artemisia ordosica is an important sand fixation plant in north China, whereas few studies were conducted on its population patterns. Population patterns of this species are therefore studied, and the aims are mainly: 1) how spatial scales are related to population patterns, 2) whether plant sizes effect population patterns, and 3) what roles environments play in the process of pattern formation? Methods Two plots in the size of 50 m×50 m were established in the Mu Us sandy land, and all the A. ordosica plants were recorded and mapped. After that, the data were analyzed with the method of point pattern analysis. Key results On the scales less than certain critical points, the population is usually characterized by non_random distribution (being clumped or regular), and their spatial association is considerably strong, but may be positive or negative. By contrast, if the scales enlarge beyond these points, the plants will disperse randomly, and their spatial association will loosen greatly. Small individuals are more likely to follow clumped distribution than those big ones. The spatial association between plants will turn from positive to negative if their size differences are enlarged increasingly. Unlike the A. ordosica plants growing in fixed sandy land, those plants in semi_fixed sandy land are easier to follow clumped distribution and associate with each other positively.  Conclusions Population patterns and spatial association of A. ordosicadepend on spatial scales, individual sizes and environments, and so do their intra_specific relationships. IfA. ordosica plants are transplanted into shifting sandy land for sand control and vegetation restoration, they ought to be arranged in the form of clumped distribution rather than regular distribution.