Roadsides as pollinator habitat: The promises and perils of roadside restorations

Pollinators are declining, and habitat loss is a major contributor. Restoring roadsides, with over 10 million acres in the USA, into pollinator habitat is one solution. To do so, we must understand how to restore roadsides into productive habitat and understand the risks associated with attracting pollinators to roads. Although we know that diverse, floral-rich native plant communities are important for pollinators, establishing these communities in roadsides is challenging. We found that the diversity and abundance of butterflies and bumblebees was the same in roadsides seeded with diverse, native seed mixes and species-poor, non-native seed mixes. This finding is likely due to unseeded colonizers invading both types of plantings and a lack of continued management. Roadsides also present unique challenges compared to other restoration sites. Pollinators are exposed to pollutants, including heavy metal emissions from cars and road salts. Heavy metals are toxic to pollinators. However, certain traits may predict pollinators’ tolerance to heavy metals in roadsides. We found that range size and, to a lesser extent, host plant mutagenicity predicted butterflies’ tolerance to heavy metal exposure. Road salts, on the other hand, often contain the essential micronutrient sodium and may attract pollinators. Previous work showed pollinators’ preference for artificial salty nectar. However, we

found that pollinator preference for naturally produced salty nectar varied by group and plant species. While more research is needed to fully understand roadsides as pollinator habitat, in many roadsides benefits likely outweigh the costs. As pollinators continue to decline, roadside restoration cannot be delayed.