GROUNDWATER LEVEL, MOISTURE SUPPLY, AND VEGETATION IN THE NETHERLANDS

The goal of this study was to establish quantitative relationships amo ng vegetation, soil, and ground water that can be used in ecological m odeling and engineering. To investigate these relationships, we used d ata from nature conservation areas in the Netherlands where phreatic g round-water levels had been measured in piezometers for at least five years. The species composition and soil composition of sites near thes e piezometers were described in detail. The data were used to investig ate the relationship between the occurrence of hydrophytes and xerophy tes versus average ground-water levels and moisture supply. We found t hat the distinction between sites dominated by hydrophytes and sites d ominated by mesophytes coincides with a mean spring ground-water level of 20-30 cm below surface. Dry sites, dominated by xerophytes, can be defined as sites where under grassland cover moisture deficits will b e more than 10 mm in an average year.