水分是半干旱区生态系统的主要限制因子。榆树疏林草原是我国半干旱区沙地的重要植物群落，是典型的水分限制生态系统。气候和土壤决定了该区域植被格局和动态，同时植被结构和格局又控制着区域土壤水分的时空变化。构建水文过程与植被互馈的生态水文模型，是量化半干旱区植被稳定性生态-水文阈值和预测未来趋势的有效途径。现有研究很少从个体尺度植物动态出发，通过模拟揭示景观尺度植被格局和水文过程的耦合机制。本研究以浑善达克沙地榆树疏林草原为主要研究区域，通过野外观测和数学分析，将个体植物冠层、根系分布与景观尺度植被格局联系，将景观尺度植被格局与土壤水分分布耦合，构建以随机降雨事件驱动的植被格局和水文过程耦合的生态水文模型。基于生态最优性原理，应用模型确定榆树疏林植被水分利用的适宜生态阈值，为区域植被恢复提供植被格局的最优配置。该研究将为榆树疏林草原天然生态系统的可持续维持和退化生态系统的恢复重建提供科学依据。

Water is the main limited factor in semiarid ecosystem. Elm (Ulmus Pumila) open woodland, which is the typical water-limited ecosystem, is the important vegetation community in sandy land located in semiarid area of China. A particular challenge is the fact that the spatial pattern of vegetation is both a cause and effect of variation in water availability in semiarid ecosystems. Clarification of the coupled ecohydrological mechanisms that determine the spatial pattern and structural characteristics of vegetation in water-limited landscapes remains a vexing problem in both hydrological and vegetation sciences. Regrettably, the coupling of individual pattern to landscape-scale distribution of soil water balance into theories regarding the dynamics of semiarid ecosystems is not as well developed. Here we develop a methodology to derive the landscape-scale distribution of water balance and soil moisture in a patchy vegetation mosaic based on the statistics of an underlying Poisson distribution of individual tree canopies and their accompanying root systems. Our model is applied to Ulmus Pumila open woodland located in Hunshandake sandy land in Northeast China. Furthermore, the ecological threshold value range of soil water availability for Ulmus Pumila openland woodland will be derived from the model according to the principles of ecological optimization that simultaneously maximizes plant water uptake while minimizing plant water stress. The research will be beneficial to maintain sustainably the natural ecosystem of Ulmus Pumila open woodland and restore from the degraded ecosystem.