Selecting target species to evaluate the success of wet grassland restoration

Abstract The evaluation of restoration success needs the definition of goals and the set up of evaluation criteria. This will be done for wet grassland restoration on fen soils in NW Germany. These ecosystems lost their habitat function for co-adapted plant species due to melioration and intensive farming since the 1950s. The recovery of this function is a major concept deduced from environmental policies. In order to evaluate the success of restoration measures in wet grassland restoration target plant species are identified. Doing this, sets of required abiotic conditions are deduced and translated into calibrated mean indicator values for plant communities [Scripta Geobot. 18 (1992) 248]. These are arranged in a successional series which is expected to occur on fens when restoration measures are realised. Thresholds of mean indicator values are used in order to select “target systems”. Four hundred and seventy three plant species that occur in the successional fen series are reduced to 136 target species using different selection criteria. For the evaluation of restoration success it is necessary to establish assemblages of target species with different indication power, invasion probability and frequency. As an indicator integrating these demands, the potential of species to occur during different temporal stages (within successional lines) on fen soils and different habitats is classified. A further ranking of these target species therefore is based on their different niche breadths and temporal persistence during secondary succession. Six vulnerability classes are established which represent species groups with gradually changing vulnerability for intensification or abandonment, respectively. Species with a narrow niche and short persistence during succession are strongly endangered by supposed changes in land management. It is clear from restoration experiments in NW Germany and The Netherlands however that these species are hardly capable of re-establishing during restoration. Higher frequencies in intensive grasslands enhance the re-invasion into recovered grassland swards. Considering this low re-colonisation rate it has to be a priority concept to protect those relic habitats still existing, especially remnants of small sedge-, wet grassland- and stream valley communities.