Open Access

Michaela Kruse, Karin Stein-Bachinger, Frank Gottwald, Elisabeth Schmidt, Thilo Heinken

• The intensification of agricultural practices has led to a severe decrease in grassland biodiversity. Although there is strong evidence that organic farming can reduce the negative impacts of land use, knowledge regarding the most beneficial management system for species richness on organic grasslands is still scarce. This study examines differences in the biodiversity of plants and butterflies on rotationally and continuously grazed pastures as well as on meadows cut twice per year on two large organic suckler cow farms in NE Germany. Vegetation and flower abundance, as factors likely to influence butterfly abundance and diversity, were compared and used to explain the differences. The data attained by vegetation assessments and monthly transect inspections from May to August were analyzed using descriptive statistics and nonparametric methods. The abiotic site conditions of the studied plots had more influence on plant species numbers than the management method. Dry and nutrient-poor areas (mainly poor types of Cynosurion) and undrained wet fens (Calthion) were important for phytodiversity, measured by the absolute number of species, indicator species for ecologically valuable grasslands and the Shannon Index. Meadows tended to have more indicator species than pastures, where small-scale special sites such as wet depressions were crucial for plant diversity. Butterfly diversity was very low, and 90% of the recorded butterflies were individuals of the generalist species Pieris napi. Butterfly abundance depended mainly on occurrence of specific habitat types and specific larval host plants. Supply of flowers was crucial only in certain time periods. Differences in butterfly abundance between the management systems could be explained by the site conditions of the studied grasslands. We conclude that meadows are more favorable to support ecologically valuable plant species; however, their extension is contradictory to the organic farming method of suckler cows maintained outside of stables. Rotationally grazed pastures could be a compromise that would enhance the temporal heterogeneity of flower abundance and vegetation structure. The plant diversity on pastures should be improved by less intensive grazing on special sites and plant species enrichment by means of hay transfer. For enhancing butterfly diversity we suggest to reduce land use intensity especially on poor soils. Considering the economic perspective of the farms, small parts of the agricultural area could be sufficient if connectivity to other suitable habitats is assured. Flower abundance and diversity of larval host plants could be promoted by high diversity of farming practices as well as pre-serving small uncut strips of meadows.
• In den letzten Jahrzehnten wurde in den Agrarlandschaften der Industrieländer ein erheblicher Rückgang der Artenvielfalt beobachtet (TSCHARNTKE et al. 2005). Grünland ist davon besonders stark betroffen. Obwohl der ökologische Landbau aufgrund des Verzichts auf Pestizide und mineralischen Stickstoffdünger sowie einer insgesamt weniger intensiven Bewirtschaftung bereits zu einer Verbesserung der Situation beiträgt (TUCK et al. 2014), kann durch zusätzliche Maßnahmen eine weitere Förderung der Biodiversität erreicht werden. Um zu untersuchen, welche Grünlandbewirtschaftungsform dafür empfehlenswert ist, wurden in dieser Studie Standweiden, Umtriebsweiden und Mähwiesen auf großen, ökologisch bewirtschafteten Mutterkuhbetrieben in Mecklenburg-Vorpommern hinsichtlich ihrer botanischen Artenzusammensetzung, der Tagfalterdiversität und -abundanzen, des Blütenangebotes und der Vegetationsstruktur untersucht. Die Ergebnisse fließen in ein Pilotprojekt zur Entwicklung eines Naturschutzstandards für ökologisch bewirtschaftete Betriebe ein (STEIN-BACHINGER et al. 2014, GOTTWALD et al. 2015). Dieser Standard stellt eine zusätzliche Qualifikation für besondere Leistungen zur Förderung der Biodiversität dar und wird auch für Vermarktungszwecke genutzt (GOTTWALD & STEIN-BACHINGER 2015).