Session

Semi-natural grasslands are crucial for the diversity of flowering plants and insect pollinators, which is facing a dramatic decline globally. The diverse range of floral traits in semi-natural grasslands typically supports various pollinator species through niche partitioning, enhancing pollination services across agricultural landscapes. However, this support is threatened by shifts in farming intensity.

We aim to link grazing regimes to the floral traits in a semi-natural grassland habitat of conservation concern in the European Union. We sampled plant species composition in 116 plots of 16m2 within extensive farms and ungrazed areas across a wide latitudinal and altitudinal range encompassing Italy and Switzerland. We measured seven flower traits relevant to plant-insect interactions and calculated functional diversity (FD) and community-weighted mean (CWM) for each trait. We compared grazed and ungrazed flowering communities using non-parametric tests; and in grazed areas we fitted piecewise structural equation models to investigate the direct and indirect, i.e., through species diversity, effects of grazing regimes on FD and CWM.

FD did not differ between grazed and ungrazed grasslands. However, grazing favoured species with big, short and pink flowers with high UV-reflectance and long flowering duration.

Within grazed areas, moderate grazing intensity increased FD of morphological, phenological traits and floral reflectance by enhancing taxonomic species diversity. Sheep grazing favoured FD of flower morphological traits. In moderately grazed grasslands, bilateral and non-yellow flowers were more abundant.

Based on our results, grazed grasslands may sustain insect pollinators, especially in seasons other than spring and summer. Promoting moderate grazing and favouring sheep over cattle may support the diversity of pollinator species either directly or indirectly through the enhancement of species diversity.