SPATIAL RELATIONSHIPS BETWEEN SITE HYDROLOGY AND THE OCCURRENCE OF GRASSLAND OF CONSERVATION IMPORTANCE - A RISK ASSESSMENT WITH GIS

The UK's Environmentally Sensitive Area (ESA) scheme provides financia l incentives for farmers to undertake management which is compatible w ith the conservation of landscapes and wildlife species. Lowland wet g rassland is an important component of a number of these ESAs. Manageme nt prescriptions relate to farming practices like grazing and weed man agement. For lowland wet grasslands, they may also include options to raise wafer levels for the benefit of species, many of which have decl ined following widespread drainage of agricultural land. This paper fo cuses on Southlake Moor in Somerset, south-west England, where raised water-level prescriptions have operated since 1992 and where an increa sed incidence of late spring flooding appears to be threatening import ant areas of nationally scarce Cynosurus cristatus-Caltha palustris gr assland. A methodology is presented which makes use of a GIS to quanti fy the distribution of the nature conservation resource and link this to a hydrological model and a database of plant water-regime requireme nts. The model predicts water-tables on a field-by-field basis for eac h 10 day period throughout the year; allowing flood maps to be constru cted. The database quantifies the water regime requirements for indivi dual species on Southlake Moor: Using individual fields as the unit of study, these two are linked within the GIS to permit the extent of sp ring flooding to be identified and its potential impact assessed in te rms of suitability for key species/communities. The paper describes ho w this approach could be used to determine whether deliberate manageme nt to raise water levels might be placing characteristic and scarce ve getation communities at risk (C) 1998 Academic Press.