|
|
| |
| |
Post-Fire Rehabilitation and
Restoration
Why is Rehabilitation
a Concern? . Hillslope Stabilization
Treatments
Soil and Sediment Traps .
Channel Treatments . Tilling
/ Scarification
Post-Fire Rehabilitation and Restoration
Publication
|
Why is Rehabilitation a Concern?
The post-fire condition of a burned landscape
directly relates to the type and condition of
the forest and the severity of the burn. Fire
ecologists use the term burn severity
to refer to the effects of fire on soil conditions
and hydrologic function. In general, the denser
the pre-fire vegetation and the longer the fire
burns on a particular site, the more severe the
effects on soil and its ability to absorb and
process water.
High severity wildfires remove virtually
all forest vegetation – from trees,
shrubs and grasses down to discarded needles,
decomposed roots and other elements of ground
cover or duff that protect forest
soils. A severe wildfire may also cause
certain types of soil to become hydrophobic
by forming a waxy, water-repellent layer
that keeps water from penetrating the soil
and dramatically amplifies the rate of runoff.
Felling
of hazard trees is one of several emergency
rehabilitation practices intended to protect
public safety. |
 |
 |
The loss of critical surface
vegetation leaves forested slopes extremely
vulnerable to large-scale soil erosion and
flooding during subsequent storm events.
These risks, in turn, threaten the health,
safety and integrity of communities and
natural resources downstream. The likelihood
that such a post-fire event will occur in
Colorado is increased by the prevalence
of highly-erodible soils in several parts
of the state and weather patterns that frequently
bring heavy rains on the heels of fire season.
The impacts of high
severity fire on a Missionary Ridge hillside. |
In the aftermath of the 2002 fire
season, the Colorado Department of Health estimated
that 26 municipal water storage facilities were
shut down due to fire and post-fire impacts.
Below are some common emergency
rehabilitation practices.
Top
|
Hillslope Stabilization Treatments
Hillslope treatments are designed to stop or
slow post-fire flooding and sediment movement.
The objective in using these treatments is to
quickly establish ground cover that protects soil
from raindrop splash, binds soil particles, increases
infi ltration and slows surface runoff.
Seeding: The most common
treatment involves aerial seeding of annual
grasses. This activity has shown limited effectiveness,
but remains the only method available to treat
large areas in a short period of time and at
a reasonably low cost per acre. Hand seeding
is often used for smaller, more sensitive areas.
In both cases, care must be taken to reduce
the risk of introducing noxious weeds.
| Mulching: Mulching has
proven the most effective at providing immediate
ground cover to sensitive areas but is also
relatively expensive and difficult to install.
Rehabilitation crews following the 2002
fires often applied a mixture of water,
wood fiber mulch, seed and sometimes fertilizer
known as hydromulch. This
treatment provides protective benefits during
the first year even if seeds are not able
to germinate. |
Aerial release
of straw mulch and seed. |
Top
|
Soil and Sediment Traps
Soil and sediment traps are designed to trap
and hold soil on the slope and more broadly disperse
overland water and sediment flows.
Contour Log Felling:
Rehabilitation workers often use burned
logs onsite to create a mechanical barrier
to water flow that also traps sediment
and promotes infiltration. Dead trees
are felled, limbed, cut to manageable
size and placed on a contour perpendicular
to the direction of the slope. Long tubes
of plastic netting filled with straw,
known as straw wattles,
are often used in the same way as logs
because they are easier and less hazardous
to place. Use of weed-free straw is critical
to avoid introducing noxious weeds |
Erosion barrier
created from a burned log.
|
 |
Silt Fences: In areas
where large-scale surface runoff with
significant sedimentation is expected,
fences hung with specially designed fabric
can be erected. Proper installation of
silt fences is critical to preventing
blowouts.
Silt fence on
Hayman Fire site. |
Top
|
Channel Treatments
Channel treatments are used to modify sediment
and water movement in stream channels, preventing
flooding and debris torrents that threaten downstream
communities and resources. These treatments often
serve to slow water flow, allowing sediment to
settle out, and then release sediments gradually
through decay.
Check Dams: Dams made of rocks,
logs, straw bales or straw wattles are placed
in small drainages to collect sediments and
slow the velocity of water traveling down slope.
Straw bales are the cheapest and easiest options,
but can be short-lived.
|
Straw bale check
dams near Cheesman Reservoir.
|
A rehabilitation
worker puts straw bales in place to slow
post-fire erosion. |
Top
|
Tilling / Scarification
In areas where burn severity has created water
repellent or hydrophobic soils, rehabilitation
often includes breaking up the hardened soil layer
to increase infiltration and improve conditions
for reseeding. This scarification can be done
by hand on steep slopes using hand-rakes known
as McLeods or it can be conducted mechanically
using all-terrain or other vehicles to drag a
harrow across the ground.
Top
|
Post-Fire Rehabilitation and Restoration Publications
The information found on this page was excerpted
from pages 8-15 in the 2003
Report on the Health of Colorado's Forests
(1.65 MB PDF). Please refer
to this report for more information on post-fire
rehabilitation and restoration.
Fact Sheets
Note: You will need Acrobat
5.0, or higher, to open these PDF files.
|
|
|
|
|
|
|
|
