Structure and spatial distribution patterns of Populus euphratica populations from different habitats in the Dunhuang Oasis

In order to investigate the age structure and spatial distribution patterns of Populus euphratica populations in different habitats, five plots, totally 6.25 hm2, were established in the Dunhuang Oasis, western China. Seven aggregation indices were measured using a contiguous quadrat method and tally inventory. The results indicated that the study area was short of saplings, and juveniles were scarce, resulting in an inverse pyramidal age structure of P. euphratica populations and showing a trend of declining populations. The P. euphratica stands were aged, sparse and dwarfish. The age structure of P. euphratica populations varied remarkably among different habitats, among which, that of HK population was the most incomplete with the rapidest declining succession. In general, the spatial distribution of P. euphratica populations conformed to a clumped distribution pattern except for the DMMT population. The age structure and the spatial distribution pattern of P. euphratica populations were closely related to biological and ecological characteristics of the species and the heterogeneous environmental factors such as landform, water resources, climate and soil.