BEHAVIOR OF WETLAND PLANT-SPECIES ALONG A MOISTURE GRADIENT IN 2 GEOGRAPHICALLY DISTANT AREAS

The occurrence of a species along an environmental gradient can be con sidered as the product of its physiological requirements and competiti ve interactions with other species. One may, therefore, expect that th is realized habitat differs between areas when a species has to co-exi st with different species. To test this hypothesis, we compared the re sponses of wetland plants to hydrological conditions in two European l owland river valleys: the Drentse A valley (The Netherlands) and the P eene valley (eastern Germany). We used mean water level and wafer leve l amplitude as hydrological parameters to analyse differentiation in r ealized habitats within species. Most species occurred in slightly wet ter conditions, with higher fluctuations in the German site but with n arrower tolerances for these parameters. We suggest that this may resu lt from a higher competition intensity for light, possibly caused by a larger local species pool and/or presence of more dominant species wi th a high competitive ability. The consequences for practical applicat ions-such as parameter estimation fbr predictive models-are discussed.