Grassland intensification strongly reduces butterfly diversity in the Westerwald mountain range, Germany

Abstract

The dramatic loss of biodiversity in agricultural landscapes poses a substantial challenge to conservation. Losses are mainly caused by an all-pervasive intensification of agricultural management over recent decades, negatively affecting a wealth of taxa including insects. Against this background, we here set out to quantify the effects of grassland management on butterflies, comprising an important indicator and pollinator group. We recorded butterflies along 47 transects in the Westerwald mountain range, western Germany, spanning an intensification gradient ranging from grassland fallows via traditionally and intensively managed hay meadows through to silage grasslands. The numbers of species, individuals, threatened species, individuals of threatened species, and additionally α-diversity and conservation value were highest on traditionally managed grasslands followed by fallows, intensively managed grasslands, and finally silage grasslands. Comparing traditionally managed with silage grasslands, losses amounted on average to 44% of species, 58% of individuals, 75% of threatened species, and 90% of individuals of threatened species. Overall, the conservation value as an integral indicator decreased by 86%. Our study indicates a near linear decrease in biodiversity with increasing management intensity (mowing frequency, fertilization), while fallows also comprised valuable butterfly habitat. This study exemplifies the dramatic loss of insects in agricultural landscapes through intensification, and highlights the value of traditionally managed grasslands but also fallows.