Naturally recruited herbaceous vegetation in abandoned Belgian limestone quarries: towards habitats of conservation interest analogues?

We examined if naturally recruited herbaceous vegetation in abandoned Belgian limestone quarries tend towards plant communities analogous to semi-natural habitats of conservation interest. We studied taxon-based assemblages (using two-dimensional non-metric multidimensional scaling ordination) and functional patterns (relative to Grime’s competitor, stress tolerator and ruderal plant strategies (CSR) classification) of plant communities (n = 360 plots) among three different time periods after quarry abandonment (< 3 y, 3–20 y, > 20 y). We compared those successional assemblages with those of habitat of conservation interest plant communities (n = 53 plots): lowland hay meadows and rupicolous, xerophilous and mesophilous calcareous grasslands. Our results indicate that naturally recruited herbaceous vegetation compositionally resembled mesophilous grassland, even though initial substrate conditions were more similar to rupicolous or xerophilous grasslands. The specific successional pathway we found in CSR state-space differs from Grime's predictions because there was a functional shift in plant assemblages from dominance by ruderals to dominance by stress-tolerant species. The differences in successional trajectories we found on different types of rock substrate suggest that conservation management should adopt a site-specific approach, recognizing that the highest probabilities of success on hard limestone will be restoration to calcareous grassland analogues.