Use of vegetation classification and plant indicators to assess grazing abandonment in Estonian coastal wetlands

Question: What are the effects of grazing abandonment on the vegetation composition of coastal wetlands in northern Europe? Location: Vormsi Island and Silma Nature Reserve in western Estonia, Europe. Methods: Local knowledge and field reconnaisance were used to identify current and historical management levels of wetland sites within the Estonian study area. Nine study sites, with varying management histories, were selcted comprising an area of 287 hectares. A total of 198 vegetation quadrats were taken from 43 distinct vegetation patches in five of the sites. Twinspan analysis was used to identify community type, and a phytosociological key was constructed for character taxa. This vegetation classification was then applied within a GIS based context to classify all the study sites, using a ground survey technique and 1:2000 scale air photos. Results: Eleven different brackish coastal wetland community types were identified. Indicator species were defined with community characteristics for the seven main vegetation types readily recognisable in the field. Of these vegetation types, coastal wet grasslands were most extensive in grazed sites, or sites that had been more intensively grazed, while abandoned sites were largely composed of Phragmites australis stands, tall grassland, and scrub. Site variations based on vegetation composition were significantly correlated with past grazing intensity. Plant community-types showed significant edaphic differences, with particularly low soil moisture and high conducitivity and pH for open pioneer patches compared to other vegetation types. Conclusion: Abandonment of traditionally grazed coastal grasslands threatens their characteristic biodiversity. This study found that grazing abandonment reduced the extent of coastal wetland grasslands of particular conservation value, typified by Agrostis stolonifera, Festuca rubra and Juncus gerardii. Nevertheless, plant species of conservation interest were found across the sequence of community types described. The study shows that grazing is an important factor influencing coastal wetland plant communities but suggests that vegetation distribution is affected by environmental variables, such as topography.