Burned Area Rehabilitation
Necessary to Control Erosion
After a fire, some or all of the ground cover will be burned
away, exposing the soil to the direct impact of rain. Depending
on the severity of the fire, the soil may also become ‘hydrophobic’ and
will repel water, rather than absorbing it. These conditions
can set the stage for flooding and soil erosion when rain
occurs.
Vegetative Recovery Quick Facts
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The
ability of a tree to withstand fire damage is based on
the thickness of the bark, rooting depth, needle length,
bud size, and degree of scorch.
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Conifers are cone-bearing
trees that reestablish only from available seed reserves.
Wind and wildlife aid in seed dispersal
into the burned area.
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Fire often prepares a suitable seedbed
by exposing mineral soil necessary for good germination.
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Aspen is unique among Colorado forest trees in its ability
to sprout new stems after a fire. Many shrubs and
grasses share this ability to resprout from underground
roots
undamaged by fire.
Soil Erosion Control Quick Facts
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The
most immediate consequence of fire is the potential for
soil erosion.
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Intense heat from fire can make the soil repel
water, a condition called hydrophobicity.
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Landowners should
take quick action to minimize erosion once it’s
safe to return to the property:
- fell damaged trees to slow water
runoff after rainfall;
- create check dams in drainages
using straw bales;
- spread straw to protect the soil and
reseeding efforts; and
- use water bars to reduce soil erosion
on roads.
An important first step to control erosion after a wildfire
is reseeding grass in the severely burned areas. Many trees
and plants can recover after fire depending on the severity
of the burn. It is important to leave existing vegetation
if the plants do not threaten personal safety or property
(hazardous trees in danger of falling should be identified
first). Note: it’s a good idea to obtain certified
seed to guarantee: variety, that it was tested under field
conditions, and that it is recommended for the state.
Hydrophobic
Soils
In severe, slow-moving fires, the combustion of vegetative
materials creates a gas that penetrates the soil profile.
As the soil cools, this gas condenses and forms a waxy coating.
This causes the soil to repel water - a phenomena called
hydrophobicity. This hydrophobic condition increases the
rate of water runoff. Percolation of water into the soil
profile is reduced, making it difficult for seeds to germinate
and for the roots of surviving plants to obtain moisture.
Hydrophobic soils do not form in every instance. Factors
contributing to their formation are: a thick layer of litter
before the fire; a severe slow-moving surface and crown fire;
and coarse textured soils such as sand or decomposed granite.
(Finely textured soils such as clay are less prone to hydrophobicity.)
The
hydrophobic layer can vary in thickness. There is a simple
test to determine if this water repellant layer is present:
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Place a drop of water on the exposed soil surface and
wait a few moments. If the water beads up and does
not penetrate the soil than it’s hydrophobic.
-
Repeat this test several
times, but each time remove a one-inch thick layer
of the soil profile. Breaking this water
repellant layeris essential for successful reestablishment
of plants.
In addition, freezing and thawing,
and animal activity will help break up the hydrophobic layer.
| These Quick Facts were produced by R. Moench, Wildfire
Hazard Mitigation Coordinator, in cooperation with the
Colorado State Forest Service. An extensive list of Natural
Resources Online Fact Sheets are available at http://www.ext.colostate.edu/PUBS/NATRES/pubnatr.html. |
The Burn Area Emergency Rehabilitation
(BAER) website can be found at: http://www.fs.fed.us/r2/psicc/hayres/baer/index.htm
Common Burn Area Rehabilitation Terms
Mulching
Mulching is the hand application of weed free straw to
parts of the burned area to replace ground cover that
has been lost.
Log erosion barrier
Log erosion barriers are dead trees cut and placed ‘on
the contour’ of the hill. Purpose is to (1) reduce
velocity of surface runoff and (2) retain soil loss
on the slope. A trench is dug and the log is laid in
it, perpendicular to the slope.
Scarification
Scarification is the plowing or disking of strips along
the contour. The purpose is to break up the hydrophobic
soil by disking the soil in strips along the contour,
about 30’ apart. This provides a ‘drain’ for
water as it moves down the slope. In addition, the
strips were seeded to provide additional stability...which
plant roots assist in.
Wattles
Wattles are a biodegradable plastic mesh filled with
weed free straw. Similar in concept to a log erosion
barrier. Used in places where the existing trees
can’t be cut or they don’t exist, such
as meadows. |
Colorado Fire-Related Websites
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