Spatial relationships between site hydrology and the occurrence of grassland of conservation importance: a risk assessment with GIS

The UKʹs Environmentally Sensitive Area (ESA) scheme provides financial incentives for farmers to undertake management which is compatible with the conservation of landscapes and wildlife species. Lowland wet grassland is an important component of a number of these ESAs. Management prescriptions relate to farming practices like grazing and weed management. For lowland wet grasslands, they may also include options to raise water levels for the benefit of species, many of which have declined following widespread drainage of agricultural land. This paper focuses on Southlake Moor in Somerset, south-west England, where raised water-level prescriptions have operated since 1992 and where an increased incidence of late spring flooding appears to be threatening important areas of nationally scarceCynosurus cristatus–Caltha palustrisgrassland. A methodology is presented which makes use of a GIS to quantify the distribution of the nature conservation resource and link this to a hydrological model and a database of plant water-regime requirements. The model predicts water-tables on a field-by-field basis for each 10 day period throughout the year, allowing flood maps to be constructed. The database quantifies the water regime requirements for individual species on Southlake Moor. Using individual fields as the unit of study, these two are linked within the GIS to permit the extent of spring flooding to be identified and its potential impact assessed in terms of suitability for key species/communities. The paper describes how this approach could be used to determine whether deliberate management to raise water levels might be placing characteristic and scarce vegetation communities at risk.1998 Academic Press