The occurence of rare and vulnerable habitats is most often linked to specific environmental conditions. Both the dereviation of nature-oriented norms as well as the management and develop- ment of nature areas require target and threshold values for crucial environmental factors at the stand level. This project aims at developing such target and threshold values for species- rich grassland and wetland ecosystems. More specifically, its objectives are (1) to deduce an appriopriate set of process parameters concerning the redox conditions, acid/base status, and nutrient availability in the rhizosphere; and (2) to assess to what extent target and threshold values for this parameters can be derived for a wide range of vulnerable habitats.