Local management at low- to moderate-intensity benefits wild bees in European calcareous grasslands while landscape conservation effects vary
Abstract
Calcareous grasslands are important habitats for many pollinators including wild bees but have declined dramatically in habitat quantity and quality due to land use changes at local and landscape scale. Such developments might be mitigated by local management, such as low-intensity land use and landscape measures, including the conservation of calcareous grasslands and the establishment of biodiversity-friendly farming practices like agri-environment schemes (AES). Yet, the effectiveness of these measures for conserving pollinator communities is still poorly explored and might depend, for example on the landscape context or the AES type (productive vs. non-productive). Using transect walks, we investigated how local and landscape-scale management affects bee communities in 96 calcareous grasslands in three European countries (Estonia, Germany, Spain), covering three biogeographic regions (boreal, continental, Mediterranean). Over a period of 2 years, we recorded 6716 individuals from 235 species across our study regions, underpinning the importance of calcareous grasslands for wild bee conservation. According to a local land use intensity index, we found that both long-term abandonment and intensive management reduced wild bee species richness and abundance, either directly or indirectly through effects on floral resource availability. At the landscape scale, cover of calcareous grassland and AES in the surroundings benefited wild bee communities, though the effectiveness of AES often depended on the AES type and the landscape cover of calcareous grasslands. In Germany, for example productive AES increased wild bee abundance and richness only in landscapes with higher calcareous grassland cover, while non-productive AES were most effective if landscape calcareous grassland cover was lower. However, landscape effects varied across study regions. Synthesis and applications. Conserving wild bee diversity in these grasslands requires avoiding long-term abandonment and intensive management, while promoting local management at low to moderate intensity. Moreover, it is essential to conserve and restore calcareous grasslands in the surroundings. This may be complemented by implementing AES in the landscape, depending on the AES type, landscape and regional context. Our findings stress that future restoration and conservation planning should combine local and landscape management measures to successfully conserve wild bees in European calcareous grasslands.
What the paper shows and why it matters (AI-generated)
Neither leaving calcareous grasslands alone nor farming them hard is good for wild bees: across 96 sites in Estonia, Germany and Spain, both long-term abandonment and intensive management cut species richness and abundance, largely by thinning out the flowers bees depend on. Landscape measures proved less predictable. Whether an agri-environment scheme helped hinged on its type and on how much calcareous grassland remained nearby, and the pattern shifted between regions — a caution against transferring a single conservation prescription across Europe.