Ecological consequences and restoration potential of abandoned wet grasslands

Wet grasslands of nature conservation importance have been maintained for centuries by agricultural management such as grazing and mowing for hay, but are now threatened by abandonment despite recent restoration initiatives. This paper is the first to synthesise published information to elucidate the main patterns, timescales, and consequences of wet grassland abandonment with an international perspective, and to evaluate restoration success. Results showed that abandonment is a particular concern in Europe, especially in central European and Baltic countries, but is also a factor in the deterioration of North American wet grasslands. In Europe, abandonment peaked in the second half of the 20th century, driven by inter-related political and socio-economic changes. Nearly all ecological studies of wet grassland abandonment (94%) focus upon vegetation and they reveal that community changes have been measured within three years, including species elimination as competitors expand and woody plants encroach. However, some wet grasslands show resilience as dominant herbaceous species can persist for up to 50 years, restricting woody invasion. Herbaceous species dominating abandoned grasslands are typically native, tall, productive and competitive grasses or sedges, while small, stress-tolerant, rare species characteristically decrease. Few studies have measured soil properties (11%) or animals (6%) during abandonment, although it seems that invertebrates may increase (for up to 20 years) and then decline in unmanaged wet grasslands. Evidence suggests that wet grasslands that have been abandoned for <40 years can be rehabilitated within 10 years by reinstating vegetation management, but fully successful restoration to a previous condition is elusive. Long-abandoned grasslands may need more interventionist restoration efforts to create regeneration niches and introduce species. Although managers should assess specific site characteristics and potential constraints before restoring abandoned wet grasslands, it is recommended that restoration initiatives should generally prioritise treeless wet grasslands with low soil nutrients that have been abandoned for <20 years.