Soil seed bank of regenerating overgrazed acidic sandy grasslands
Abstract
Spontaneous regeneration of four degraded sandy grassland sites was studied. Our aim was to evaluate spontaneous regeneration capacity of acidic sandy grasslands after overgrazing by domestic geese. Three hypotheses were tested using long-term vegetation records and seed bank data. (i) S short-lived, early successional species comprise the majority of the seed banks and late successional perennials have sparse seed banks. (ii) Composition of seed banks is more similar to pioneer vegetation than to later successional stages. (iii) 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 the percentage cover of vascular species was recorded in five 4 m2 sized permanent plots, three times a year between 1991 and 2002. In the last year of the study (2002) 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. Annuals and short-lived perennial dicots comprised the majority of the seed bank. The dominant perennial graminoids also built up dense seed banks. Seed density varied between 10300 and 40900 seeds/m2. Significantly higher seed densities were found in upper sites than in lower ones. We found a low to medium similarity (Jaccard similarity <0.45) between vegetation and the seed bank; similarity was the highest with the vegetation of the 1994–1998 period, except for the year of the seed bank sampling. The vertical position of sites had a significant effect on the regeneration after overgrazing. The large cover of grasses in lower sites decreased species richness and it also decreased seed densities by preventing seed set of annuals and short-lived perennials. Here, further management practices (e.g. grazing) are needed to increase species richness.
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