Plant diversity differs between young and old mesic meadows in a central European low mountain region

Effects of habitat age on species diversity are an important issue in plant conservation. However, effects of habitat age on mesic meadows are poorly investigated. Here we compare plant species richness between old mesic meadows (>150 years) and young mesic meadows (40-60 years) in a low mountain region (Thuringian Forest, Germany). Species richness and species traits were determined in 20 old and 20 young mountain meadows (alliances Polygono-Trisetion, Violion caninae) which were defined using historical maps and compared using species indicator analysis and ANOVA. Additionally we quantified changes in the extent of the area of young and old meadows using a Geographical Information System. Species richness of vascular plants on 20m² plots was significantly higher in old than in young meadows, while evenness did not differ between young and old meadows. Endangered plant species were restricted to old meadows, which also contained a higher proportion of habitat specialists. The terminal velocity index of seeds was lower and seed weight was higher in old meadows, indicating a lower importance of wind dispersal in old meadows. This was also indicated by a higher proportion of species with seeds adapted to wind dispersal in young meadows. In old meadows there was a higher proportion of species with seeds adapted to ant dispersal and a lower proportion of species with seeds adapted to animal dispersal. In a representative sub-area of the study region, the total area of meadows has increased by 88% during the 20th century due to transformation of arable fields into meadows, while the area of old meadows declined by 36% during the same time due to abandonment and afforestation. We conclude that the age of the habitat is highly important in order to maintain plant diversity of mesic meadows. Therefore, higher priority should be given to old meadows.