The persistence of calcareous grassland species in the soil seed bank under developing and established scrub

The relationships between the composition of the soil seed bank, the field layer vegetation, and the scrub canopy were investigated along a 69 m transect, grading from incipient woodland, through scrub, into intensively rabbit-grazed calcareous grassland. The results are used to assess the persistence of species associated with open calcareous grassland in the seed bank under developing scrub. Scrub age, composition and density, changed along the transect from the woodland to open grassland. A total of 35 forb and grass species were found in the field layer. The pattern evident in the scrub layer was also reflected in the herbaceous vegetation. The field layer in the most closed portion of the transect, where the scrub was oldest, was dominated by shade-tolerant species normally associated with woodland habitats. The abundance of these species decreased along the transect as the scrub age declined, and the field layer became increasingly dominated by species typical of open grassland. A total of 47 species germinated from the seed bank. Few species were recorded in the seed bank along the entire length of the transect. Overall, the seed bank was dominated by Hypericum perforatum and Centaurium erythraea, which accounted for 38.2% and 28.6% of emerging seedlings respectively. As with a number of similar studies, the composition of the seed bank had a low correspondence with the composition of the field layer vegetation. The results also emphasise that the composition of the seed bank can be viewed as an ‘ecological palimpsest’, with germinable seed of species from each stage of the old-field succession occurring in the soil. The seed bank is an important component in the re-vegetation of an area after disturbance such as scrub removal. This study supports the findings of previous research in showing that relatively few characteristic calcareous grassland species form persistent seed banks. The soil seed bank would therefore appear to be of limited value in the restoration of such grassland following scrub removal.