[RWG] ARTICLE: Promoting Native Roadside Plant Communities and Ensuring Successful Vegetation Establishment Practices

[Krone, Elizabeth C]

Shawn D. Askew, Ph.D., James M. Goatley, Ph.D., and Clebson Gonçalves, Ph.D.,
Virginia Transportation Research Council, March 2023

Abstract or Summary

The loss of vegetation from roadside activities can lead to erosion and an increased
sediment load in stormwater ponds. Current VDOT procedures regarding approved seed blends
and establishment practices have led to inconsistent vegetation establishment and greatly rely on
introduced species. Growing concerns regarding the threat of introduced, invasive species have
increased the promotion of native plants in landscapes. One example is VDOT’s participation in
the Candidate Conservation Agreement for monarchs fostering a desire to better understand
factors that may improve milkweed abundance. Native seed blends, however, have failed to
produce soil stabilization or long-term establishment in the past, presumably because of
erroneous species selection, seed dormancy, and competitive displacement by weedy vegetation.
Empirical evidence suggests that several native plant species have colonized Virginia roadways,
despite years of seeding introduced species. This study was conducted to (1) identify and
document potential procedural improvements for successful roadside vegetation establishment in
Virginia; (2) propose candidate native plants for VDOT see blend consideration based on a
statewide plant community assessment on Virginia roadsides; and (3) summarize the literature on
availability, cost, and establishment success of candidate native species.

A review of VDOT’s vegetation establishment practices indicates that procedural
inconsistencies related to the development of Roadside Development Sheets and recent
restrictions on fertilizer application may be contributing to vegetation establishment failures. A
statewide plant community assessment evaluated 490 sites and identified 616 unique plant
species among the 67,330 plants surveyed. The Shannon Diversity Index was calculated for
2,450 10-m transects, indicating that plant biodiversity was higher on low-maintenance distal
backslopes compared with high-maintenance road edges, shoulders, and ditches. Plant
biodiversity was also higher on secondary roads than on primary roads. The unique introduced
species encountered were relatively stable across Virginia’s seven ecoregions, but unique native
species were more ecosystem dependent. Unique native species increased from 114 species on
the road edge and shoulder to 281 species on the distal backslope. The likelihood of encountering
a native plant increases from 1 in 4 on the road edge to 1 in 2 on the distal backslope.

Among the native plants that were most frequently encountered, seeds were often
unavailable or price prohibitive. Andropogon virginicus, Tridens flavus, Dichanthelium
clandestinum, Tripsacum dactyloides, and Sorghastrum nutans have desirable attributes as native
roadside grasses and are among the top 20 most commonly encountered native grasses on
Virginia roadsides. The average cost of the seed for these grasses was $59 per pound compared
with $2.40 per pound for tall fescue. Among grasses that are currently not commercially
available, Setaria parviflora, Eragrostis pectinacean, Dichanthelium laxiflorum, and Panicum
anceps are among the top 10 most commonly encountered native grasses and have characteristics
that would be desirable for roadside vegetation. Other species were tabulated in the report based
on frequency of occurrence, topographical transect, and other environmental factors. At least one
milkweed species was observed at 37 out of 490 sites statewide (7.6%). The report recommends
that VDOT explore opportunities to improve understanding of procedural policy and to
implement procedural improvements, including revisions to the roadside development sheet.
Additional opportunities for research include testing native plants for establishment and long
term dominance.

Link to article: https://www.virginiadot.org/vtrc/main/online_reports/pdf/23-r14.pdf


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