Different environmental conditions in lowlands and uplands highlight challenges for butterfly conservation in Central Europe

Studies from all over the world have recently reported severe declines in insect diversity and abundance. Due to their high sensitivity to environmental changes, butterflies are well-suited indicators for assessing the overall state of the terrestrial insect fauna. Though they rank among the best-studied insect groups, Europe's butterfly populations are still declining in many places, especially in landscapes under intensive land use. In this study, we investigated the response of butterfly assemblages to environmental conditions in 169 plots in the wider countryside of North Rhine-Westphalia (NW Germany, Central Europe). Our study revealed a strong relationship between butterfly species richness and density and the environmental conditions in the study area. Due to the maintenance of low-intensity land use, the uplands were characterised by more favourable conditions for butterflies and consistently had a higher species richness and density of species overall and of threatened species than the intensively used lowlands. In addition to elevation, landscape diversity in particular fostered butterfly diversity. By contrast, butterfly assemblages exhibited a negative response to urban areas and arable land, which were among the most dominant habitat types in the lowlands. Moreover, our study highlighted the importance of nutrient-poor grasslands for butterflies, which is mainly a result of their high habitat quality. According to the findings of our study, it is especially important to promote heterogeneous landscapes with a large extent of semi-natural, nutrient-poor habitats. Therefore, the key issue for butterfly conservation is to change the current farming policies to increase the amount of low-intensity farmland. •Uplands provide better conditions for butterflies than intensively used lowlands.•Strong negative response of butterfly assemblages to urban areas and arable land.•Landscape heterogeneity and nutrient-poor habitats foster butterfly diversity.•Low-intensity land use is of outstanding importance for butterfly conservation.•Conservation actions beyond the management of protected areas are needed.