Abstract

In plant ecology, site is a central concept. A site is the place where a plant species or plant community grows, and the site provides the set of conditions in which it lives. Within an initially homogeneous parent material, gravity-driven groundwater flow influences the site conditions through the spatial distribution of nutrients and other relevant chemical agents. Especially upward seepage may produce and maintain site conditions that are essential for various relatively rare plant species and communities. Increased attention to upward seepage among ecologists has resulted in cooperation with hydrologists and the emergence of a discipline of its own - eco-hydrology - on the boundary of two scientific fields, linked by the site concept. In the Netherlands, a simple classification of water types, based on the groundwater's subsurface history, was applied for compiling a nationwide geographical database on ecologically relevant upward seepage. Correspondence analyses of this database with data on plant-species occurrence demonstrate that in poor Pleistocene sandy soils upward seepage explains the occurrence of some species and communities quite well, whereas in fluvial plains and polder areas with richer clay soils the influence of seepage is blurred by the importance of soil characteristics. It is concluded, therefore, that plant species may be used as seepage indicators in rapid assessments and surveys, but that constant awareness of the limitations is required.