Investigating the value of citizen-led gardens on road verges for insect biodiversity in the City of Merri-bek, Australia

Quantifying the benefits of urban greenspaces for conservation is a key goal of urban ecologists, as cities continue to expand and threaten biodiversity globally. Road verges represent a substantial portion of urban greenspace that contains simplified vegetation and considerable opportunity for habitat additions. This study focussed on an inner area of Melbourne, Australia, where citizen-led gardens on verges are common, as residents take advantage of the space and opportunity offered by roadsides in their neighbourhood. Although council guidelines for planting in these spaces recommend native vegetation, many residents have opted for a variety of exotic species, resulting in a diversity of verge gardens throughout the municipality. This study assessed the effectiveness of these citizen-led gardens as habitat for native insects. We identified 7 verge gardens and 7 control sites, where we measured site features (floral cover, floral richness, species richness) and the abundance and species richness of three insect groups (bees, beetles, and butterflies). Insect abundance and species richness were higher at garden sites than control sites and positively associated with the species richness of vegetation. These relationships indicate that citizen-led gardens on road verges with a variety of plant species and aesthetics can contribute to local pollinator biodiversity. Further, our results can inform council guidelines on designing verge gardens to benefit native-insect biodiversity. • Road verges are abundant in cities and make up a large area of underutilised space. • Some citizens take advantage of local road verges and plant gardens. • Pollinator diversity on these gardens is higher than on standard (lawn) road verges. • Floral abundance and diversity drive native bee biodiversity on road verges. • Strategic planning of road verge habitat could promote urban insect conservation.