Threatened herbivorous insects maintained by long term traditional management practices in semi natural grasslands
Biodiversity declines have been driven by land use changes in semi natural grasslands worldwide. This is thought to be because threatened species are unable to compete with generalist species, which are better adapted to the new environments created by modern land use management. Many studies have separately examined biodiversity declines resulting from land abandonment and intensified use, however few have examined their unified effects on biodiversity. In addition, we still do not fully understand the relative importance of decreasing habitat area in comparison to changes in land use practice with regard to biodiversity. To clarify the roles of these interconnected variables, we compared the diversity of threatened and common herbivorous insects and plants among four land use types (traditional, annual burning, annual mowing, and abandoned) during 2012 and 2013. Next, we examined whether a relationship exists between herbivorous insects and environmental variables (species richness of plants, as well as current and historical grassland areas) We showed that land use changes (annual burning, annual mowing and/or land abandonment) diminished the diversity of threatened butterflies, orthopterans, and plants. Herbivorous insects were affected by land use practices rather than grassland area. Our results suggest that to conserve threatened species in semi natural grasslands, we should reintroduce traditional land use practices in areas that currently experience modern practices, such as annual mowing and burning. The reintroduction of traditional management practices would allow for the recovery of plant biodiversity, thereby increasing herbivorous insect diversity.