Abstract
Plant diversity of the Dutch landscape is most I y restricted to semi-natural and natural ecosystems in nature reserves. Many endangered plant species, have, however, been declined in the last decades, because of environmental stresses, such as air pollution, eutrophication or lowering of the water table. Several semi-natural ecosystems of high nature conservation importance on the sandy Pleistocene areas have been especially affected. Ecological restoration has to play a vital role in reducing these negative effects and to reinstate the damaged plant communities. Species-rich wet heaths and NARDO-GALION SAXATlLIS grasslands were once wide spread and locations of 'hot spots' of diversity in these relatively species-poor surroundings. Is was shown that these species-rich ecosystems on sandy soils were restricted to oligotrophic, but weakly buffered wet soil conditions, mostly originating from seepage with buffered (local) groundwater. Acidification, caused by atmospheric deposition and lowering of the water table, is thus a serious threat for the maintenance of these species-rich situations, together with the enhanced N accumulation. It has been found that suitable hydrological measures, in combination with sod cutting, can rehabilitate acidified and eutrophied wet soils by allowing seepage of buffered groundwater. This relative quick response is related with the presence of some endangered plant species in the soil seed bank and seed sources in nearby sites (<500 m). Serious constraints for the restoration of many of these communities are when the seepage water is acidified and an ammonium pulse occurred after restoration. The research aims of this project are (1) to elucidate the significance of high ammonium concentrations after sod cutting and its importance for the establishment of characteristic species; (2) to quantify the effectiveness of the reloading of the depleted cation exchange complex with different quality and quantities of seepage water; together with its fine tuning for the growth requirements of characteristic endangered species; and (3) to determine the actual seed bank of endangered species in these degraded situations. The final objective of this project is to develop a robust restoration approach for former hot spots of diversity in acidified wet heaths and matgrass swards and to deliver a set of abiotic and biotic factors needed for a successful field implementation.
Netherlands