Disturbance regimes in dry sandy grasslands – past, present and future

Sammanfattning: A number of sandy grassland habitats of interest for biodiversity conservation can be found in Europe. One such habitat is the threatened xeric sand calcareous grassland, which is home to a large number of endangered species. It is characterized by a discontinuous vegetation cover, mainly consisting of stress-tolerant species favoured by nutrient-poor and dry conditions. The xeric sand calcareous grassland habitat has declined during the last century due to intensification of farming, afforestation, abandonment, acidification and nutrient enrichment. Understanding the land use history has proven crucial for the conservation of biodiversity in the agricultural landscape. Land use was traced back to the 18th century, and land use history was compared with the amount of bare sand, lime content and P availability. Previous agricultural activity was found to have created these habitats in flat areas lacking natural disturbance. However, ploughing was probably not the factor retaining CaCO3 in the top soil. Instead, it seems very likely that it was the wind erosion, promoted by cultivation, which counteracted depletion by exposing the CaCO3 rich sand. The largest changes in land use took place more than 100 years ago. Areas that were recently cultivated had the highest levels of extractable P, which may pose a threat to biodiversity. The restoration potential of topsoil removal and soil perturbation in degenerated xeric sand calcareous grassland was investigated. Restoration actions performed in 2006 resulted in increased pH and reduced nitrogen availability. Early colonisation of the key species Koeleria glauca after both deep perturbation and topsoil removal was found. The proportion of target species in 2012 was 20% after topsoil removal, compared to 30% in target vegetation, and less than 1% in controls. Deep perturbation lead to 7% target species, while almost no effects of shallow perturbation could be seen. The increased pH after soil perturbation also resulted in increased species richness of bryophytes. Six red-listed beetle species associated with open, dry grasslands were found after soil perturbation, out of which four were found only in perturbated plots. The availability of propagules is a key factor for the re-establishment of plant species in grasslands after restoration. The seed rain and the seed bank of xeric sand calcareous grassland in southern Sweden were investigated with the aim to assess the potential contribution of soil seed bank and natural seed rain for the re-establishment of threatened plant species after habitat restoration. Most target species had a negligible persistent seed bank. Many target species were well-represented in the within-patch seed rain, but seed dispersal seemed to be very limited beyond the natal population.