Effects of a dense moss layer on germination and establishment of vascular plants in newly created calcareous grasslands

From 2003 to 2005, a sowing experiment was carried out over 26 months in newly created xerophytic grassland on calcareous gravel in order to show the effects of moss layer removal on vascular plant germination and establishment. Hand-collected seeds of Biscutella laevigata, Bromus erectus, Carex humilis and Linum perenne were sown on experimental plots with intact and removed moss layer. Germination percentages under controlled conditions in a germination chamber were about 80% for all species except for C. humilis (14%). No germination of C. humilis was detected throughout the field experiment. The moss layer significantly reduced germination and seedling survival of Biscutella, Bromus and Linum. On all plots, seed germination was highest in October 2003 and continued in spring and summer 2004 to a lesser extent. Seedling mortality was highest during dry periods in summer 2004 and 2005. In winter 2004/2005, mortality showed a peak on plots with removed moss layer, but not on plots with intact moss layer. This indicates a protective role of the moss layer against heavy frosts.The barrier function and shading caused by mosses were probably the most important factors with negative effect on germination and establishment of the studied vascular plants. Water deficiency and high temperatures seemed to be the main hazards for survival of young plants as the moss layer offered no protection against these factors.