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Directional Log Felling Fact Sheet
What is Directional Log Felling?
Directional Log Felling is a way to reduce the erosive impact of raindrops and
the amount of rain water that runs down a slope by cutting trees such that they
fall perpendicular to the main direction of the slope.
When is Directional Log Felling Used?
Directional Log Felling is used on burned slopes where there are
a number of dead trees that have little or no alternative value. When the
original ground cover is lost after a fire the soil is at risk for erosion.
Additionally drainage ways may flood more frequently due to increased runoff
from the burned slopes. Directional Log Felling is a way utilize the dead timber
for some beneficial purpose. However consideration for the wildlife habitat
value of the dead trees should be given prior to clear cutting, even in areas
where all trees have been killed by the fire. Also note that Directional Log
Felling in a burned area is dangerous due to a significant risk that trees may
drop branches on workers or fall over completely with little or no warning. Logs
or slash from the felling should not be placed in drainage ways or swales. When
unanchored the logs or debris may be washed downstream causing damage to
drainage improvements or blockage of natural channels resulting in increased
erosion.
How is Directional Log Felling Accomplished?
Sawyers cut the trees, dropping the trunks across the slope (perpendicular to
the direction water runs) as much as possible. Stumps are left about 12"
high to brace the tree from sliding downhill. Tree limbs are removed to the
extent necessary for the log to lie flat on the ground, encouraging the
collection of water and trapping the debris moving down slope. For this practice
to be most effective, enough trees must be felled to create a barrier that
interrupts the movement of water down the slope, as shown in the theoretical
pattern depicted by Figure 1. In reality the theoretical pattern is only a
guide, as it is rarely achievable in a natural setting.
How Effective is Directional Log Felling?
When there are 400 to 600 feet of logs available per acre, especially in the 6
inch to 12 inch size range, Directional Log Felling may significantly increase
infiltration, add surface roughness, and replace some lost cover, thus reducing
a slope’s erosion potential. At best Directional Log Felling provides short
term protection on slopes that require re-establishment of permanent vegetation
for long term erosion control. Directional Log Felling has little effect when
logs are oriented up and down the slope instead of across it, when felled logs
are not in contact with the soil, where the slope is steeper than 50%, and where
the density of logs is less than 300 feet per acre.
FIGURE 1 - Theoretical Pattern for Directional Log Felling
NOTE: After a fire many trees are weakened from burning around the base
of the trunk. The trees can fall over or blow down without warning.
Shallow rooted trees can also fall. Therefore be extremely alert when
around burned trees.
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