Abstract: Based on the 2006 investigation data in lower reaches of Heihe River, and by using logarithmic normal distribution model, the models about the vegetation cover of Populus euphratica and Tamarix ramossima and the groundwater level in study area were built, and the potential plant of the study area was simulated. The results showed that in the lower reaches of Heihe River, the optimal groundwater level and mean groundwater level for P. euphratica were 2.6 m and 3.6 m, and those for T. ramossima were 2.0 m and 3.0 m, respectively. The high cover P. euphratica distribution area was mainly concentrated in the near-banks of Donghe River and Xihe River, while higher cover T. ramossima was distributed in most parts of the study area. From the aspect of current groundwater level, T. ramossima should be the adaptive species in the study area. The similarities between the potential and actual spatial distribution of P. euphratica and T. ramossima were 43.4% and 55.6%, respectively, and the main reason for the lower similarity was that there existed a gypsum salt pan in soil, which blocked the vertical movement of soil water.

Key words: field scale, soil water content, spatial variability, sampling spacing