Date of this Version
Schacht, W. and Wu-Smart, J. (2019). "Establishment of Wildflower Islands to Enhance Roadside Health and Aesthetics". NDOT Research Report SPR-1(17) M058.
Wildflowers are crucial in the ecological function of the low-input roadside plant communities in terms of water andnutrient cycling, nutrient inputs such as nitrogen, total plant canopy cover, stand longevity, and provision of habitat for numerous small animals. Further, wildflowers provide critical foraging and nesting resources for birds, insects, and other wildlife. Unfortunately, habitat loss from agricultural and urban development has led to rapid population declines in wild bees and other pollinators across the US, thereby jeopardizing not only food production but also the sustainability of our natural landscapes (Kearns & Inouye, 1997). One way to mitigate wild bee decline is to establish more habitat corridors on public rights-of-way, such as roadsides. Planting pollinator-friendly native wildflowers on roadsides provides nutrient-rich forage and nesting resources for bees and is aesthetically pleasing. With 97,256 miles of public roadways in Nebraska (~4 million miles of roadways in the United States), roadsides play ever increasing roles in sustaining biodiversity within our state and beyond.
Federal guidelines state that wildflowers are to be used in roadside seeding mixtures, and NDOT includes a diversity of wildflower species in its seeding mixtures. However, these complex seeding mixtures are often expensive because of the diversity of species and high seed price of many of these native species, particularly the wildflowers which compose roughly 10% of the total seeds but represent 30% of the total cost of seed mixtures. Further, wildflowers on roadsides are typically seeded with competitive grasses and are costly to establish and manage long term. This research explored ways to improve wildflower establishment by separating wildflower seeds from the conventional seed mixture with includes both wildflower and grass seeds. Additionally, wildflower plots were seeded at different patch or island sizes to assess cost-effective ways of reducing competition by nonnative weeds and enhancing the longevity of roadside habitat. Optimal patch sizes and treatment groups included 100% wildflower mix seeded to the entire 3 m x 18.3 m plot (treatment 100), only 50% of the plot seeded in one continuous patch (treatment 50) or in two small patches (treatment 25x2) compared to current practices of seeding wildflower-grass mixtures (treatment conventional). Ecological benefits of roadside habitat, wild bee abundance, diversity, and nesting activity was assessed and compared across seeding practices and patch size treatments. Floral diversity and abundance were also analyzed to compare plant-pollinator interactions across treatments.
Conventional roadside seeding methods yielded plots with lower abundance and richness of forbs and bees compared to plots seeded with wildflowers only (treatments 100, 50, 25x2) but only in the first year of establishment. Bee richness was highest in the late season, while forb abundance and richness were highest in the mid-season. No differences were observed across differently sized wildflower-only patches likely because of the recent establishment of plots. In fact, only ~50% of seeded forbs had established and roughly 14 plants out of the 40 species in the seed mixture did not establish in either survey years and may therefore be replaced in future seed mixtures. Our results indicate that wildflower segregation in strips or islands may be a cost-effective method of improving wildflower establishment and persistence in diverse roadside mixtures. As plots mature and become vulnerable to weed encroachment, the effect of patch size may become more distinguished across treatment groups, therefore, further monitoring and research may be necessary to further address issues with low establishment and high competitive pressure from volunteer species. This data contributes to NDOT’s ongoing pursuit to more effectively establish wildflowers on roadsides and to better understand the role floral enhancements have on supporting and sustaining vulnerable wildlife, such as our pollinator communities.