Roadside Revegetation

IMPLEMENTATION GUIDES
system delivers seeds can be adjusted and must be calibrated prior to mulching to obtain the
desired seed density (see Section 10.3.1, Seeding, for seed calibration methods). Recalibration
should be done when seed rates or mulching rates have been changed.
Fertilizers – It is difficult to evenly apply fertilizers through a mulch blower system. Outside of
mixing fertilizers in the mulch prior to placing it into the mulch bins, fertilizing must be done in a
separate operation, either before or after mulching. Applying fertilizer through a hydroseeding
system after seedling establishment is one strategy for increasing available nutrients on the
site. As discussed in Section 10.1.1, Fertilizers, the delayed timing of fertilization reduces the
risk of nutrient leaching and increases the probability that nutrients will be available at the
levels needed for established plants.
Erosion Mats
Erosion mats are manufactured blankets or mats designed to increase surface stability and
control erosion. They are available in strips or rolls with a minimum thickness of 0.25 inch.
Erosion control revegetative mats or rolled erosion controlled products are applied directly
to the soil surface for control of sheet erosion and to aid the establishment of vegetation. Turf
reinforcement mats are materials that are filled with soil when installed to increase surface
soil strength (Kemp 2006).
There are a multitude of products on the market, with a range in design and costs. Determining
which products will serve your project needs at the right price can be challenging. Several
state departments of transportation periodically evaluate and compare the shear stress, soil
erosion protection, longevity, and other characteristics for these products (Caltrans 2003; Kemp
2006) and these documents are usually available on the internet. Since the installed costs of
erosion mats can be very expensive, it is important that the job is done right. Taking the time
to select the appropriate erosion mats, native species mix, and seed placement techniques is
essential for assuring that revegetation is successful. Small field trials using different species
and erosion mats can help in these decisions (Figure 10-21).
The same characteristics that create an optimum environment for seed germination in other
mulches are also important to consider when selecting erosion mats. Typically, those materials
that protect the seeds from drying out but allow light and space for germinating seeds to grow
into seedlings will perform best for vegetation establishment. The thicker erosion mats with
the most loft should have better conditions for seedling establishment than thinner materials.
The drawbacks to erosion mats are generally not in the product itself, but in how it gets applied
to the site. Poorly applied erosion mats can result in sheet and rill erosion under the fabric.
A B C D
Figure 10-21 | Field trials of species and materials
Small field trials can help select the most appropriate
species and materials for a project. The trial shown in this
picture compared straw mat (A and B) with a polywoven
mat (C and D). It also compared the growth of blue wild rye
(Elymus glaucus) and California fescue (Festuca californica)
(A and C). The first year results indicated that there was
much better establishment of grasses on the polywoven
erosion mat than the straw mat, yet no difference in species
growth. Maintaining the trial for two years showed that
California fescue outperformed blue wild rye. These results
led to using California fescue and polywoven erosion mat
for the project described in Inset 10 3.
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
246