Consequences of succession on extensively grazed grasslands for Central European butterfly communities : rethinking conservation practices

Because of changes in land use, the quantity of extensively grazed or mown calcareous grasslands and their successional stages have drastically declined over the last few decades in Central Europe. Old fallow land has decreased most. It is often afforested or reconverted into extensively cultivated grassland because extensive cultivation is believed to be favorable for diversity and rare species conservation. The relative importance of fallow calcareous grasslands, however, has not been investigated fully and might be much underestimated. To evaluate the relative importance of extensively grazed pastures, early and old fallow land, and young forest, we examined populations of diurnal butterflies from 14 sites in the Swiss Jura Mountains. We used univariate, multivariate, and qualitative methods to compare the successional stages. The first 2-3 years of succession had little influence on the butterfly fauna. Therefore, pastures and early fallow land were treated as a single "early stage." Old fallow land had significantly higher species richness (+32%) and heterogeneity (+65%) and hosted more Red List species (+48%) than the early stage. Young forest was depauperate in butterfly species. Further, cluster analysis and correspondence analysis showed a close resemblance of the sites of the early stage to each other and a clear difference from the sites of old fallow land. All differences were best explained by the successional age of the sites. Both early stage and old fallow land showed a high proportion (<25%) of stage-specific species, but more threatened species were specific to old fallow land. We conclude that up to now the importance of old fallow land has been underestimated in conservation efforts in Central Europe. Contrary to the prevailing opinion, it is at least as important for butterflies as extensively cultivated grassland. Further conversion into forest, a common habitat in the region, should be prevented. Because old fallow land has becomeexceedingly rare, its inclusion in management plans is urgently needed. Otherwise, we may soon lose a valuable but often overlooked part of our biodiversity. Betr. Schmetterlinge im Nordwestschweizer Jura