Roadside turfgrass seed mixtures: models and figures

Roadsides in urban areas are often seeded with turfgrass mixtures to
provide ground cover and reduce weed abundance. Designing mixtures to
withstand exposure to biotic and abiotic stress is challenging. Research
from managed and natural ecosystems have shown that increasing plant
species richness and diversity can increase groundcover and suppress weed
cover, but it is unclear whether such relationships hold in roadside
environments. Our objective was to determine the effect of seeded
turfgrass species richness on ground cover and weed suppression alongside
roadsides in diverse regions in Minnesota. We tested six turfgrass species
in monocultures, two-way mixtures, some three-way mixtures, and a single
six-way mixture at seven sites seeded in the fall of 2018, and seven sites
seeded in the fall of 2019. Seeded turfgrass, weed, and bare soil coverage
was measured at each site over two growing seasons. There was a positive
relationship between turfgrass species richness and turfgrass cover, and
this interaction effect increased over time. We found that increasing
turfgrass species richness reduced bare soil coverage. Turfgrass cover was
also more consistent across research sites (i.e., greater spatial
stability) with increasing species richness. Our results show that
positive relationships between plant species richness and groundcover hold
in highly disturbed and managed roadside environments. These findings can
improve the design of seed mixtures for roadsides and in other ecological
contexts where vegetative cover is important.