Roadside Revegetation

IMPLEMENTATION GUIDES
adjacent to roads. The upper portions of steep, extensive slopes are typically not reachable
by straw blowers.
When straw is used as a seed mulch, it is important that the application rates are not so deep
that a physical barrier is formed. A minimum depth that has been shown to control evaporation
is one inch (Slick and Curtis 1985). Applying too much straw will restrict sunlight and growing
space for establishing seedlings. A rule of thumb is that some surface soil (15 percent to 20
percent) should be visible through the straw after application (Kay 1972, 1983; Jackson and
others 1988). This equates to 1.5 to 2 tons per acre, depending on the type of straw and its
moisture content.
Straw is susceptible to movement with moderate to high winds. Tackifiers are often applied
over the straw to keep it in place (Kay 1978). Products such as guar and plantago are used with
low quantities of hydromulch to bind straw together (Manufacturers have stated application
rates for this purpose). Straw can also be crimped, rolled, or punched into the soil. These
measures will stabilize the straw by burying portions of the stems into the soil and can increase
erosion protection because of the more intimate contact of straw with the soil surface. The
potential for compaction is increased with these treatments and the tradeoffs of offsetting
surface stability with long-term soil productivity should be weighed.
Wood Strands and Wood Wool
Wood strands and wood wool are commercially available wood products used for mulch. Wood
strands are long, thin pieces of wood produced from wood waste veneer whereas, wood wool,
known as excelsior, is produced from aspen wood. These products are developed as an effective
erosion control alternative to straw and hay (Foltz and Dooley 2003). The advantages of wood
strands over straw are that it is free of seeds, has a longer life, and is more resistant to wind.
Wood strands, like straw, form a stable cover with high porosity or loft, characteristics which
are important for controlling soil moisture and temperature around the germinating seeds.
The large spaces or pores created by the wood strands allow space, light, and protection for
young emerging seedlings (Figure 10-13). Unlike straw, these materials keep their structure
or porosity over time, and do not compress with snow or lose fiber strength through decomposition.
While the performance of this new product as a seed cover has not been tested, it
has all the characteristics of being an excellent seed cover. The application rates for wood
strands are likely to follow the guides for straw – at least 15 percent to 20 percent of the soil
surface should be visible. This is likely to be greater than the recommended rates for erosion
control. Installing small test plots of varying thicknesses of mulch would be a good means
to determine the appropriate thickness for optimum seed germination. Wood strands are
delivered in different size bales and applied by hand or through straw blowing equipment
(Figure 10-23). As with straw, this product is limited by the accessibility of the site by hay
transportation and blowing equipment.
Litter and Duff
Litter is the layer of fresh and partially decomposed needles and leaves that cover the surface
of most forest and shrub plant community soils. Duff is the dark, decomposed layer directly
below the litter layer (leaves and needles are not identifiable in the duff layer) that is high in
nutrients and humus. In addition to providing soil protection and nutrients, litter and duff can
also contain dormant, yet viable, seeds from species that make up the forest or shrub plant
communities. When litter and duff are collected, they should be matched to the appropriate
revegetation site. For example, litter and duff collected from cool, moist sites should not be
applied on hot, dry sites.
The depth that litter and duff accumulates will vary by species composition, age, and productivity
of the plant community. Dense stands of ponderosa pine can produce thick layers of litter.
More open forest stands on dry, less productive sites will have thinner layers of duff and litter
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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