Sown and self-seeding species in planted wildflower meadows increase floral abundance and richness in a Scottish semi-natural coastal grassland

Background
Reduction in available floral resources has contributed to global pollinator decline. Suitably managed urban habitats can provide high floral resources, with potential to support pollinator populations. Here we quantify the consequences of planting native wildflower meadows in peri-urban unimproved coastal grassland in Edinburgh, Scotland.

Methods
We compared seasonal patterns in floral abundance, richness, and composition between eight replicate sown native wildflower meadows and eight paired semi-natural grassland plots over three years (2021–2023). We distinguished contributions of planted (sown seed mix) and unplanted (self-seeding, non-seed mix) species in planted meadows.

Results
We surveyed a total of 191,642 floral units of 72 species. Meadow and grassland plots showed significantly different seasonal phenologies and between-year variation in flowering species composition. Many species absent from the sown seed mix (including most surrounding grassland species) also flowered in the meadow plots, contributing to significantly higher overall meadow floral species richness. Floral abundance was significantly higher in planted meadows, and higher in seed mix than non-seed mix species.

Conclusion
Planted native wildflower meadows offered consistent enhancements to floral richness and abundance, through both planted and unplanted species. Contrasting compositions and phenologies of grassland and meadow flower assemblages provide a greater diversity of trophic rewards for pollinators than either would alone.

Key policy highlights

Planting of a wildflower meadow mix at eight coastal sites near Edinburgh increased floral abundance and species richness relative to comparison plots of unmown semi-natural grassland.

As well as meadow seed-mix species, non-seed mix flowering species also contributed to floral abundance and species richness in meadow sites, particularly early in the year.

The combination of planted meadows and unmown semi-natural grassland supported more flowering species through the year than either habitat alone.

Meadow preparation using a sterile bed technique did not eliminate perennial weeds such as creeping thistles and docks. Ongoing weeding is required to prolong attractiveness to human visitors.