Constraints in the restoration of ecological diversity in grassland and heathland communities.

Species-rich grassland and heathland communities still occur in low-intensity farming systems in many European countries. Gradually, such systems have either been abandoned or more intensively exploited, with a subsequent decrease in species numbers. Until recently, it was thought that restoration of these communities would be straightforward. However, abiotic constraints (with respect to eutrophication and acidification) have hampered restoration more than previously thought. Moreover, very recent research has revealed that biotic constraints can also be important: many plant species are not present in the soil seed bank and their dispersal is limited in the present fragmented landscape.