FIRE EFFECTS GUIDE - National Wildfire Coordinating Group

. Adjacent, unburned "control" sites should be used for comparison with burned
sites whenever possible to evaluate the effects of fire on soils or water. A
biometrist or statistician should be consulted for appropriate sampling and
comparison methods. 3. Limited Ability to Extrapolate to Other Sites. Much of
the fire literature describes the effects on soils and hydrology of intense wildfires.
Such information should be extrapolated to different regions, soils, environmental
conditions, types of fire behavior and characteristics, and to prescribed fires with
caution.
4. Variability of Effects. Because fire effects on soils and water are highly
variable, consideration should be given to locally documenting effects and relating
the effects to fireline intensity, burn severity, fuel, duff, and soil moisture content at
the time of the fire, and other appropriate factors.
5. Factors Related to Postfire Erosion. Potential for wind, water, or gravity
(especially dry ravel) erosion should be given strong consideration in the timing
(i.e., fall vs. spring) of prescribed fires, and in the methods, timing, and species
proposed for emergency fire rehabilitation.
a. Delayed recovery of vegetation and slope steepness appear to be important
factors in accelerated erosion.
b. The presence of large woody debris and duff after a fire helps to protect the soil
from erosion.
6. Management of Soil Heating. The amount of soil heating caused by prescribed
fires in forest or woodland areas can be managed.
a. The distribution of soil heating is affected by the choice to broadcast burn, pile
burn, or burn windrows. Also, the piling method may be important because
machine piles tend to be "dirtier," and hold heat longer, than hand piles.
b. Small diameter, unmerchantable trees (whips) can be slashed just before fire,
when they are still green and will not burn well, and thus can contribute little to soil
heating.
c. Higher levels of utilization or yarding some unmerchantable material in areas
with heavy dead and down fuel loads can decrease the amount of potential soil
heating.
d. Burning an area while moisture content of large diameter fuels, lower duff, and
soil is high will limit the duration of the fire and the amount of heat penetration into
lower soil layers.
e. Rapid ignition techniques (e.g., aerial drip torch) can sometimes be used to
shorten the duration of the burn, and thus the amount of soil heating.