Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
drier sites, but soil strength is limited to the surface of the soil profile where the roots are most
abundant. For this reason, grasses and forbs do not provide as much stability (Figure 5-63).
On potentially unstable sites, grasses should be grown between shrub and tree seedlings to
add soil strength to the surface soil while tree and shrub species become established. On dry
sites, however, grasses must be excluded around seedlings or vegetative cuttings until they
have become established. Because of the steep, shallow nature of many of these sites, planting
seedlings is not always practical or successful. Hydroseeding or hand sowing, covered by a
surface mulch that will protect the surface from erosion for several years while the shrubs
become established, should be considered.
Soil Improvement
Improving soil productivity will increase root densities and enhance slope stability (Hall and
others 1994). Mitigating measures that improve water storage, organic matter, and nutrients
should, with time, increase slope stability. Some practices, such as soil tillage, reduce soil
strength in the short-term. However, once plants have become established more roots occupy
the soil and slope stability is increased. Tillage should be integrated with practices that quickly
reestablish vegetation to ensure that slope stability is not compromised in the short term. On
slopes where root strength is critical for stability in the first year after construction, irrigation
could be considered to quickly establish a dense vegetation cover.
Temporary Soil Stabilitation
It is important to implement erosion control practices that stabilize the surface of steep slopes
while vegetation develops a strong root system and top growth. Where trees are inappropriate
because of clear zones and shrubs inappropriate because of sight lines, erosion control products
work well to stabilize soils while grasses and forbs establish.
5.8 WEEDS
The unwanted vegetation on a project site and surrounding area is referred to, in this document,
as weeds. Roadsides are often major conduits for the transportation of weeds, which can
be problematic not only for roadside ecology but also for the general ecosystem health of
surrounding lands and economic well-being of adjacent farmers, ranchers, gardeners, and
other land managers. A poorly revegetated roadside contributes to the spread of weeds and
detracts from environmental health. However, the implementation of a good revegetation
plan can benefit surrounding environments. The best revegetation plans focus not only on
controlling weeds, but on establishing healthy native plant communities that are resistant to
the invasion of weeds.
The term weeds denotes any species that limits successful revegetation due to increased
competition for site resources (light, nutrients, moisture). The comprehensive species list,
developed during the vegetation assessment (Section 4.6.1, Vegetation Assessment), identified
those species on the federal, state, or local lists of noxious weeds or invasive species. These
species were identified from the PLANTS database (http://plants.usda.gov). A further review
of the comprehensive species list will identify aggressive species that may not be on the
state weed lists but may be important to control. Since these lists are frequently updated, it
is important to check the most current lists.
The potential for weed species to become established after construction is a function of two
factors:
◾◾
Growing environment – Areas within the construction project that are favorable for
weed establishment. These areas are often highly disturbed sites with bare soils.
◾ ◾ Weed sources – There are two general sources of weeds, those existing on the site or
near the site prior to construction and those brought into the project as a result of road
construction. Sources of existing weeds are existing seed banks or plant propagules in
the project or adjacent to the project. Weed sources that are brought into the project
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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