Roadside Revegetation

IMPLEMENTATION GUIDES
from clearing and grubbing that can be chipped or mulched on site to produce various types
of wood mulch (Figure 10-19). In the past, this material has been burned or hauled to waste
areas for disposal. With greater burning restrictions and higher hauling costs, chipping these
materials and returning them to disturbed sites as mulch are practices that are becoming
more common.
Wood Fiber Mulch Production – Creating mulch from right-of-way clearing woody material
requires planning and coordination. First the road contractor piles the woody right-of-way
clearing debris into “slash piles.” These piles include tree boles, bark, branches, and stumps,
but must not contain large rocks or other inert materials that can cause wear or damage
to the equipment. When clearing and piling is completed, a company that specializes in
processing wood waste is contracted (typically by the road contractor). In this operation,
equipment is brought to each slash pile and materials in these piles are processed into mulch.
The resulting wood mulch is either placed in piles adjacent to the slash piles or transported
to designated storage sites. The timing of these operations should consider the possibility of
limited equipment use due to fire restrictions, which typically occurs in the western United
States from mid summer through early fall.
If undesirable plant species are included in the slash piles, spread of these species is likely to
occur when they are processed and applied as a mulch. This can be prevented by identifying
these plant populations on site during the weed assessment (see Section 5.8.1.1, Weed Sources
– How to Assess) and avoiding placing them into slash piles.
It is important to define the desired mulch characteristics prior to processing the piles. For
example, the size and shape of the wood particles will determine their stability and propensity
to move off the slopes, causing clean-up issues. Long strains of wood particles tend to be more
stable than short strains because they knit togher. Obtaining the proper size and dimension
can be difficult since there is a variety of wood waste reduction equipment, producing different
dimensions and fibrosity (the degree that wood fibers are separated). Specifying the particle size
and shape by stating a screen size the material must pass does not always produce the desired
material. Screens only sort for two dimensions, and not for length or fibrousness. Identifying
the type of waste reduction equipment can narrow the type of mulch produced (Table 10-5).
For example, mulch produced by shredders is long and fibrous (Figure 10-18A and B), whereas
mulch produced from chippers has close to equal length sides, with fibers still intact (Figure
10-18C). Visiting with mulch company representatives and viewing the type of products they
produce is a good way to determine the types of products you can expect to receive. If this is
not possible, have them send you samples of different mulch products. Typically, the coarser
the size of the mulch, the cheaper will be production costs since more mulch of coarser size
can be produced in a given time frame than smaller textured mulch. Other factors, such as tree
species, moisture content, and portion of tree processed, will affect the characteristics of the
Table 10.5 | General types of wood waste reduction equipment
General Equipment Types Examples Feedstock Particle Geometry
Chippers Disc Chippers, Drum Chippers whole logs, clean residuals clean edge, two-sided
Hogs
Swing Hammer, Fixed Hammer,
Punch & Die, Mass Rotor
wood waste, stumps, land clearing
debris
coarse, multi-surfaced, fibrous
Shredders
Low Speed-High Torque, High
Speed
wood waste, stumps, land clearing
debris
coarse, multi-surfaced, fibrous
Hybrids Knife Hogs, Pan & Disc wood waste, stumps, land clearing
debris
semi-coarse
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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