Summary1 Although habitat loss and fragmentation are assumed to threaten the regional survival of plant species, their effects on regional species dynamics via seed dispersal and colonization have rarely been quantified. 2 We assessed the impact of habitat loss and fragmentation on the connectivity, and hence regional survival, of wind-dispersed plant species of nutrient-poor semi-natural grasslands. We did this using a new approach to relate quantified habitat loss and fragmentation to quantified colonization capacity. 3 We quantified loss and fragmentation during the 20th century of moist, nutrient-poor semi-natural grasslands in study areas in the Netherlands, as well as their current distribution. After testing how well the habitat distribution matches species distributions of two wind-dispersed grassland forbs ( Cirsium dissectum , representative of species with long-distance wind dispersal, and Succisa pratensis , representative of species with shortdistance wind dispersal), we combined the habitat distribution data with simulated seed dispersal kernels in order to quantify the impact on connectivity. 4 Habitat loss and fragmentation has dramatically reduced both the area (by 99.8%) and the connectivity of the grasslands. The remaining grasslands are practically isolated for seeds dispersed by wind, even for species with high wind dispersal ability (for which, interestingly, connectivity by wind dispersal decreased most). Linear landscape elements hardly contribute to connectivity by wind dispersal. Regional survival of the studied species has become completely dependent on the survival of a few large populations in nature reserves. Other remaining populations are decreasing in number and size and have low colonization capacity. 5 Habitat loss and fragmentation have drastically changed the regional species dynamics of wind-dispersed plant species, indicating that it is of utmost importance to preserve remaining populations in nature reserves and that the probability of colonization of new or restored sites is very low, unless the sites are adjacent to occupied sites or dispersal is artificially assisted.

Summary 1.Restoration of formerly species-rich wet heaths and matgrass swards has not always been successful. The constraints on this restoration process are not yet fully understood and need further investigation, particularly the accumulation of ammonium in the soil after sod cutting, i.e. the removal of the vegetation and topsoil layer. This accumulation is known from sod cutting experiments in dry heaths, but had not previously been studied in wet heaths and matgrass ecosystems. 2. In 2000, sods were cut from two degraded Dutch wet heaths. Soil chemistry and germination in the sod-cut plots were measured at irregular intervals between April 2000 and August 2001. To test the influence of ammonium on germination and survival, a glasshouse dose-response experiment was conducted with two endangered wet heath plant species. 3. In both wet heaths, an accumulation of KCl-extractable ammonium up to 600 µ mol kg − 1 dry soil was found in the upper 10 cm of the soil within the first year after sod cutting. These high ammonium concentrations lasted for about 10 months. Germination was very low in the sod-cut plots in 2000 and 2001, and few target species were found, although they were present in the vicinity. 4. The dose-response experiment indicated a significant, negative correlation of both germination and survival with increasing ammonium addition for both plant species. Mean soil ammonium concentrations of the control, 100 and 250 µ  ammonium treatments were significantly lower than those of the 500 and 1000 µ  ammonium treatments (47, 45, 70, 144 and 252 µ mol kg − 1 dry soil, respectively). 5. Maximum concentrations of KCl-extractable ammonium in the field corresponded to water-extractable concentrations that were higher than those found to be limiting germination and growth in the glasshouse experiments. The low germination in the field is likely to have been adversely affected by high concentrations of ammonium as a result of sod cutting. 6. Synthesis and applications . High ammonium concentrations occur in wet heaths following sod cutting. Low rates of germination of restoration target plant species occur under such conditions. To increase the success of wet heath restoration, the accumulation of ammonium after sod cutting should be prevented by additional measures, such as liming. Because sod cutting is also applied as a restoration measure in the restoration of other ecosystems, such as fens, the effects on increased soil ammonium concentrations need further attention.