Restoration of species-rich limestone grassland communities from overgrown land: the importance of propagule availability

A held experiment was established in the eastern coast of the Baltic Sea to test the relative roles of the availability of propagules and light competition in the restoration dynamics of a former calcareous grassland overgrown by pine (Pinus sylvestlis L.). The treatments were: clear-cutting of trees with additional grazing and transplantation of sods from an open grassland with all possible sources of propagules. Species richness and composition were studied on a small-scale during 7 years in the transplanted patches of 20 x 20 cm and in their surroundings of 50 x 50 cm. In the cut and grazed site the species richness increased. Transplantation of sods from an open species-rich grassland did not result in higher richness even in their closest surroundings. In the forest, transplanted patches lost their high species richness by the second year. In the cut and grazed site, transplanted patches remained species-rich, but after 3 years, control patches reached the same level of species richness. In landscapes where former species-rich limestone grasslands are overgrown, but the local species pool has not yet changed, restoration of semi-natural grassland communities does not require the additional input of diaspores of grassland species. Transplantation of sods is potentially important method of community restoration in case of impoverished local species pools. (C) 1998 Elsevier Science B.V. All rights reserved.