Abstract: [Objective]The objectives were by investigating Halostachys caspica populations with three underwater depths:shallow (<2.5 m), middle (2.5-4.5 m) and deep (>4.5 m) in the sample plots, alluvial fan of south Junggar basin to study spatial pattern and spatial association of the populations among three underwater depths and at development stages, and to explore the impacts of underground water depth on the formation of spatial patterns and mechanism of maintaining H. caspica populations. [Method]Three 1 hm² permanent sample plots were established and grid method was used to investigate population distribution in south Junggar basin. Ripley's K function was employed to study spatial pattern, intraspecific association and their relationships with underground water depth.[Result]The number of regenerated young seedlings decreased severely with the increase of underground water depth. The population structure changed obviously due to increased dead standing trees. At different developmental stages, all H. caspica populations displayed aggregated distributions at small scales in all the three habitats. With the increase of scales, aggregation intensity weakened at different developmental stages. It was found that aggregated distribution was at 50 m scale in areas with shallow and middle underground water depth, while the population spatial pattern tended to be random distribution in areas with deep underground water. The population aggregation intensity increased with underground water depth, and young seedlings of H. caspica appeared to have obvious aggregation distribution and maximum aggregation intensity. The aggregation intensity and the scale of H. caspica population decreased from seedlings to adult trees. At small scales, intense positive association occurred in areas with shallow and middle underground water depth, while negative association was found among different population developmental stages in areas with shallow underwater depth. No association or weak negative association at big scales in areas with middle underground water depth. The populations all tended to have no association among different developmental stages in areas with deep underground water depth.[Conclusion]Underground water depth has important effect on spatial pattern and intraspecific association of H. caspica population in south Junggar basin. Especially, the deep underground water depth severely restricted the spatial pattern of the populations. In areas with middle underground water depth, the populations may be recovered by artificial measures to maintain the stable spatial pattern.

Key words: spatial pattern, spatial association, g(r) function, Halostachys caspica, Junggar basin