Do restored calcareous grasslands on former arable fields resemble ancient targets? The effect of time, methods and environment on outcomes.
A great deal of money is being invested in calcareous grassland restoration on arable land within agri-environment schemes in the European Union. There is, however, little evidence that the target ecosystem can be obtained from the restoration techniques and management practices currently used. We evaluated these techniques using a multi-site approach in order to improve the success of future restoration efforts. We compared 40 restoration sites with 40 paired reference sites and addressed the following specific hypotheses: (i) Are plant communities of restoration sites becoming more like those of mature calcareous grassland? (ii) How long does the restoration process take? (iii) Are there any environmental filters that hinder the process? (iv) Is there a difference in plant attributes between restored and ancient grassland communities, and between restored communities of different ages? We used a multivariate approach to assess the similarity of sites and found that there was little overlap between restored and ancient grassland communities even after 60 years. Successful restoration of calcareous grasslands is achievable but the process is slow. Different plant attributes were present at different frequencies in restored and reference sites, and the frequency of some attributes became more like those of reference sites with increasing age of restored site (e.g. perenniality and ruderality). Seeding restoration sites with a low diversity mix appeared detrimental to restoration. Sites that regenerated naturally moved towards the target over time, although success was limited by proximity to ancient grassland vegetation. High soil phosphorus concentration was detrimental to restoration. Synthesis and applications. We recommend selecting restoration sites with low phosphorous concentrations that adjoin patches of ancient calcareous grassland. Seed mixes should be devised carefully to prevent the assembly of low-value, competitive, stable communities dominated by grasses; natural regeneration may avoid this, but will only be effective close to sources of propagules. Other methods of restoration or habitat management would undoubtedly benefit from similar multi-site evaluation.