VEGETATION CHANGE ON THE OUSE WASHES WETLAND, ENGLAND, 1972-88 AND EFFECTS ON THEIR CONSERVATION IMPORTANCE

A re-survey of wetland vegetation on the Ouse Washes in 1988 shows that it has changed dramatically in 16 years. Glyceria maxima swamp (National Vegetation Classification S5) and Agrostis stolonifera-Alopecurus geniculatus inundation grassland (NVC S13) have more than doubled their area, whereas Phalaris arundinacea swamp (NVC S28), Holcus lanatus-Deschampsia cespitosa coarse grassland (NVC MG9) and Carex riparia swamp (NVC S6) have declined by at least three-quarters of their previous area. Increased flooding, especially in the late spring and early summer, and reduced levels of grazing and hay-making are believed to have caused these changes, with increased flooding probably the single most important factor. The vegetation changes have resulted in a reduction of plant species diversity in grazed, hayed and unmanaged Washes, but especially in the unmanaged Washes. They may have also affected ornithological use of the site but this requires fuller investigation. © 1990.