Groundwater can have a profound effect on water availability to vegetation in temperate climate regions. Here we attempt to model groundwater, soil water, and vegetation dynamics in groundwater controlled ecosystems and to assess how these depend on climate and topography. We focus on the possible location of a boundary between two vegetation types on a slope. One vegetation type is adapted to wetter soil moisture conditions, and one is adapted to drier conditions. We hypothesized that the vegetation type boundary along the slope in climax state is located where the slope-average evapotranspiration is highest and/or where vegetation stress is minimal. Vegetation stress is a combination of occurring water stress as defined by Porporato et al. (2001) and a newly defined oxygen stress, which results from anaerobic conditions. To study this system, we built a two-dimensional model of saturated-unsaturated flow along a slope in which the abundance of two vegetation types varied along the slope. The results show that boundary between the vegetation types based on maximum evapotranspiration occurs at approximately the same location as that is predicted based on minimum plant stress. When precipitation increases, the boundary between the two vegetation types moves up slope. Sensitivity of the location of the vegetation boundary to changes in precipitation decreases with increasing slope angle.