Pollinators such as rusty-patched bumble bees and monarch butterflies, critical to our eco-system, are at risk due to the loss of native habitat. A University of Minnesota research team, with support of MnDOT and the Local Road Research Board, studied whether restored roadsides could provide safe habitats for declining pollinator populations.
The researchers began by determining where pollinator-friendly habitats should be prioritized, what plant communities are created by current revegetation practices, and how pollinators use them.
They evaluated a pollinator-friendly mapping tool, which was positively associated with bumblebees, that could be refined to target specific species. This could help prioritize the stretches of road that would be cost effective to be enhanced, since native plant seed mixes can be more expensive than non-native plantings.
They also sought to understand how well native and non-native seed mixes establish in the compacted and chemically unique soils of roadsides. They revisited roadside sites that had been seeded with native versus non-native seed mixes to collect data on plant and pollinator communities 2-20 years after planting.
Seeding with native plants works – these sites had a significantly higher number of native flowering plants than sites seeded with non-natives. The team found that pollinator abundance in roadsides was related primarily to flowering plant abundance, regardless of whether plants were native. Still, the diversity of pollinator communities was positively related to the diversity of the flowering plant community.
However, the effect of seeding is short lived. The plant community is similar between native and non-native sites a few years after seeding, as seeded plants dwindle, and invasive plants become more common. This finding presents an opportunity to experiment with maintenance practices to see if long-term outcomes can be improved at sites seeded with native plants.
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