Data from: Long-term nutrient addition and grazing exclusion determine flower abundance, diversity and community composition in high-latitude grasslands

The abundance and composition of flowers within plant communities shape
the resources available to flower-visiting insects. However, it remains
unclear how nutrient enrichment and changes in grazing impact plant
communities and their floral resources, and whether these effects
contribute to ongoing pollinator decline. We investigated how the
abundance, diversity, and species composition of flowers (excluding
graminoids) respond to long-term nutrient additions and grazing exclusion
in two high-latitude grasslands (tundra and montane). We used two
factorial experimental designs: 1) a nutrient experiment with additions of
nitrogen (N), phosphorus (P), and potassium (K with micronutrients, and 2)
a grazing experiment that included combined NPK addition with and without
grazing exclusion. Flower abundance was assessed in 5 × 5 m experimental
plots after 6–10 years of treatments. N and P interactively affected
flower abundance, with N counteracting the positive effects of P. N
reduced flower abundance in the montane grassland, whereas P and K
increased it. Grazing exclusion increased flower abundance, with its
effect amplified under NPK addition, but this joint treatment reduced
flower species richness. Grazing exclusion reduced flower species
diversity, with contrasting site-specific effects depending on NPK. N, P,
and K addition, as well as grazing exclusion and NPK addition, changed the
composition of flower assemblages. At the montane grassland, joint NPK
addition and grazing exclusion led to strong dominance of forbs, such as
Anthriscus sylvestris and Geranium sylvaticum, and grazing exclusion led
to homogenisation of the flower community at the montane grassland. Our
study demonstrates the importance of grazing and nutrients as key
determinants of floral resources, which are vital for flower-visiting
insects. We suggest that quantifying floral resources could contribute to
ecosystem status assessment. Our findings offer insights for managing and
conserving pollinator habitats in the face of environmental change.