Soil Seed Bank after Eighteen Years of Succession from Grassland to Forest

Abstract

I studied the vegetation and seed bank in an 18-yr-old, replicated experiment with grazed and ungrazed plots in a semi-natural, perennial grassland in southern Sweden. In the ungrazed plots, a tall (16-20 m) and dense tree layer had developed. There were fewer plant species growing in ungrazed plots than in grazed plots, but the difference was not significant. However, the number of species per square metre was significantly lower in ungrazed plots. Hence, on a smaller scale, the ground vegetation had become less diverse, but on a larger scale few species had been lost. In the seed bank, a few species lost from the vegetation were still present as seeds in the soil, but in most cases species lost were not recorded in the seed bank. Seeds of species that had colonized plots over the 18 yr were evenly distributed in the soil between the upper (0-4 cm) and lower (4-8 cm) sampling depths. Most of the seeds of species that had disappeared from plots were deep in the soil. Hypotheses about changes in the seed bank during secondary succession, predicting decrease in species richness and seed density, were not confirmed