Seed Bank and Vegetation Development of Sandy Grasslands After Goose Breeding

Abstract

Four hypotheses were tested using long-term observations of vegetation development (12 years) and present-day seed bank data in a sandy grassland area overgrazed by domestic geese: i) Gap regeneration is crucial in maintaining species richness; thus, closed vegetation of the lower sites prevents continuous establishment of short-lived species. ii) Short-lived, early successional species comprise most of the seed banks and late successional perennials have at most sparse seed banks. iii) Composition of seed banks is more similar to pioneer vegetation than to later successional stages. iv) The similarity is higher between vegetation and seed banks in the upper-positioned plots than in the closed, lower-positioned ones. Two sites, located in the upper part of dune slopes, and another two, positioned on the lower part, were studied. In each site five 2?×?2 m permanent plots were surveyed between 1991 and 2002. Percentage cover was estimated three times a year. In the last study year, soil seed banks were sampled. Two vertical segments (0�5, 5�10 cm) were separately analyzed. The seedling emergence method was applied on concentrated samples. We found that the vegetation developed from open, annual dominated weedy assemblages to grasslands dominated by perennial graminoids. In the lower-positioned sites perennial clonal grasses (Cynodon dactylon, Poa angustifolia and P. pratensis) formed more closed vegetation, which was accompanied by lower species richness compared to the upper-positioned sites. Seed density varied between 10,300 and 40,900 seeds/m2. Significantly higher seed densities were found in upper sites than in the lower ones. Annuals and short-lived perennial dicots comprised most of the seed bank. The dominant perennial graminoids also built up dense seed banks. We found a low to medium similarity between vegetation and the seed bank; similarity was the highest with the vegetation of the 1994�1998 period. In the upper sites the similarity between seed bank and the vegetation of the last studied years was also high. The vertical position had a significant effect on regeneration after overgrazing. The large cover of grasses in lower sites decreased species richness and it also decreased the seed density preventing the seed bank formation of annuals and short-lived perennials. Here, further management practices are needed to increase the species richness.