The seed banks of English lowland calcareous grasslands along a restoration chronosequence

Abstract

We investigated whether the seed banks of ex-arable lowland calcareous grasslands underwent restoration similar to that of the above-ground restoration, and whether this was influenced by seed-sowing or environmental conditions. We compared 40 sites, where some form of restoration work had been implemented between 2 and 60 years previously, with 40 paired reference sites of good quality calcareous grassland with no history of ploughing or agricultural improvement. We analysed differences between sites and between above- and below-ground vegetation using both a multivariate approach and proportions of selected plant attributes. Seed banks of reference sites were more characteristic of late successional communities, with attributes such as stress tolerance, perenniality and a reliance on fruit as the germinule form more abundant than in restoration sites. In restoration sites, these tended to decrease with restoration site isolation and increase with restoration site age and where soil nutrient conditions were more similar to reference sites (i.e. with relatively low phosphorus and high nitrogen). Seed bank communities of all sites differed considerably from above-ground communities, however, and no overall significant responses to site age, isolation or soil nutrients were detected by multivariate analyses of similarity of species between pairs of sites. Responses to different seeding methods were also barely detectable. While there is some indication from the plant attribute data that the regeneration potential contained in the seed banks of restored sites increasingly resembles that of references sites over time, even seed banks of good quality calcareous grassland are dominated by ruderal species. It is likely, therefore, that permanent seed banks do not facilitate the restoration of ex-arable grasslands.