Potential for the restoration of lowland and wet grassland upon ex-arable land
Concerns about the impacts of intensive agriculture in the 20th century led to the introduction of policy initiatives intended to halt environmental deterioration and reverse biodiversity losses. In England, agri-environment schemes have enabled deintensification of agricultural land management and active promotion of habitat types of conservation value within the farmed landscape. One such habitat, lowland wet grassland, is represented within several Environmentally Sensitive Areas (ESAs), including the Upper Thames Tributaries (UTI) ESA. Current UK agri-environment schemes provide the policy context for this study. An investigation to determine whether soil seed banks of former, and extant, floodplain grasslands could contribute to the restoration of floristic diversity concluded that propagule availability was likely to be a major constraint on restoration and recreation of wet grassland as seed banks are too depauperate for restoration of all species. At the beginning of the study, there was some doubt as to the efficacy of ESA prescriptions for reversion of arable land to wet grassland, which involved sowing a limited range of grass species only. Site-specific floristic targets for wet grassland recreation at an ex-arable site in the UTT ESA were derived using a reference habitat. Several treatments, based on the re-introduction of species as seed, were formulated to test whether sowing a wider range of species would be more effective in generating the type of species-rich grassland aimed for under the ESA scheme. The effectiveness of the seed treatments, including the ESA scheme's recommendation, at re-establishing species-rich wet grassland on ex-arable land was assessed in a field experiment which tested the site-specific targets developed and evaluation criteria. Results concurred with those of the seed bank investigation: restoration of diversity requires the introduction of increased numbers of species. The evaluation criteria developed enable progress towards the target to be quantified, but emphasise that reference conditions must be chosen with care. Targets developed using a reference habitat were site-specific and unrealistic in the short-term. Objective, catchment-wide targets can be derived from the species distribution dataset for the study area using a number of approaches to enable identification of: (i) extant high quality lowland wet grassland - to be protected and to act as 'sources' of propagules for restoration; (ii) priority sites for restoration ('sink' fields), according to their potential to be restored to the target habitat; (iii) species that are constant in extant wet grasslands and that should form the basis of species-rich seed mixtures; and (iv) habitat-specific 'indicator species' to evaluate restoration success. Re-creation of characteristic lowland wet grassland in the UTT ESA will be possible, although early ESA recommendations for reversion of arable land, based on simple management prescriptions and low intervention, will not achieve even the poorlydefined scheme objectives. The ESA scheme could make an increased contribution to the promotion of biodiversity within the UK by targeting high quality wet grasslands for protection, and sites for restoration based upon the ease with which species-rich grassland could be established. The 'value for money' of the scheme could be increased by careful selection of species for (re-) introduction and by monitoring the success of restoration using habitat measures based on the characteristics of the target habitat to identify why restoration may be failing and where further intervention may be required.
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