Fire Rehabilitation Treatments
 Fire rehabilitation treatments are designed to reduce soil erosion and
stabilize highly erodible soils. The proper implementation of these
techniques can greatly reduce erosion during moderate precipitation.
Boulder County Open Space is using a variety of fire rehabilitation
techniques: contour log felling,
contour
straw wattles, seeding, and mulching
to restore the Walker Ranch burned area.
Burned area rehabilitation treatments are usually effective for 10 to
25 year precipitation events. However, even with aggressive burned area
rehabilitation techniques, some surface flow and erosion is likely to
occur.
Fire rehabilitation efforts will focus on the Tom Davis Gulch area, a
watershed that drains into South Boulder Creek. Severely burned areas
cover about 168 acres of the 2,400 acre Tom Davis Gulch watershed, which
is only about 7% of the watershed area. The following techniques are being
used.
When the original ground cover is lost during a fire, the soil is at
risk for erosion. Drainage ways may flood more frequently from increased
runoff on the burned slopes. Contour log felling can reduce erosion
from rainwater that runs down a slope by cutting dead trees so they fall
perpendicular to the main direction of the slope. This technique is used
on burned slopes where about 50% or more of the tree canopy is destroyed.
Sawyers cut trees, dropping the trunks along the contour of the slope
leaving stumps about 12 inches high to brace the tree from sliding
downhill. Tree limbs are removed so that the log lies flat on the ground.
Soil is then packed under the log to slow the flow of water and facilitate
the deposition of sediment on the upslope side of the log.
 Straw
wattles are used on severe to moderately burned slopes with less than 30
percent of the original ground cover remaining. They increase
infiltration, add roughness, reduce erosion, and help retain eroded soil
on slopes. They are also used to supplement erosion control in areas that
do not have enough large trees for contour log felling and in rocky areas
where contour log felling is difficult to implement.
Straw wattles are cylinders of compressed weed-free straw. They are
made of either wheat or rice straw, and are 8 to 12 inches in diameter and
20 to 25 feet long. They are encased in jute, nylon, or other
bio/photo-degradable materials. When installed on the contour of a slope
they form a continuous barrier that intercepts water and sediment running
down the slope. Straw wattles are effective for about 3 years.
 Seeding
is a commonly used burned area emergency rehabilitation treatment.
Short-lived native and non-native species are seeded to provide temporary
soil stabilization on severely burned areas during native species
regeneration. Seeding is also used to stabilize fire lines and compete
against noxious weeds that flourish after fires, particularly diffuse
knapweed.
Minimal seeding will be used since this fire was relatively small and
there are ample native seed sources surrounding the burned areas. Seed
will only be hand broadcast onto areas that are at high risk for severe
erosion or noxious weed invasion. The following seed mix is being used:
-
28% of the mix will be Blue grama (Bouteloua
gracilis), a dominant native grass,
-
25% will be Mountain brome (Bromus marginatus),
a pioneer native grass,
-
32% will be Slender wheatgrass (Elymus
trachycaulus), a short-lived native perennial, and,
-
15% will be "Regreen", a sterile hybrid
of Cereal wheat (Triticum aestivum) and Tall wheatgrass (Elytrigia
elongata), short-lived perennials.
 Mulching
reduces the erosive action of raindrops hitting bare soil and overland
sheet flow. Certified weed-free winter wheat straw is applied at 1 ton
(about 50 bales) per acre. Seeds remaining in the straw will germinate and
provide a temporary ground cover until native plants can reestablish.
Mulching is also used in conjunction with seeding to provide a
protective cover for seeds by reducing soil moisture evaporation.
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