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Contour Log Felling

What is Contour Log Felling?

Contour log felling is a way to reduce the amount of water that runs down a slope by cutting trees so that they fall perpendicular to the main direction of the slope (to lie along the contour).

When is Contour Log Felling Used?

Contour log felling is used on burned slopes where there are a number of dead trees that have little alternative value. When the original ground cover is lost after a wildfire, the soil is at risk for erosion. Additionally, drainageways may flood more frequently due to increased runoff from the burned slopes. Contour log felling is a way to use the dead timber for some beneficial purpose. Consider leaving some dead trees for wildlife habitat.

Also, note that contour log felling in burned areas is dangerous due to a significant risk that trees may fall down or drop branches on workers with little or no warning. If you do not have the equipment or skills to do this work, you can hire experienced contractors.

Logs or slash from the felling should not be placed in drainageways or swales. When unanchored, the logs or debris may be washed downstream, causing damage to drainage improvements or blocking natural channels, resulting in increased erosion.

How is Contour Log Felling Accomplished?

Trees are cut so that the trunks drop across the slope perpendicular to the flow of water. Stumps should be left about 12 inches high to be used along with stakes or stable, standing trees at each end of the log to brace it 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 debris moving down the slope. A trench eight to 12 inches deep should be dug on the uphill side of each log to catch debris. This soil should be tamped into gaps between the log and the ground to prevent water from eroding under the log.

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.

How Effective is Contour Log Felling?

When there are 400 to 600 feet of logs available per acre (about 30 logs 20 feet long and 10 inches in diameter), contour log felling may significantly increase infiltration, add surface roughness, and replace some lost cover, thus reducing erosion potential. At best, contour log felling provides short-term protection on slopes that require reestablishment of permanent vegetation for long-term erosion control.

Contour 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 percent, and where the density of logs is less than 400 feet per acre.

Recommended Horizontal Spacing
Slope Gradient (percent) Low Fire Intensity Medium Fire Intensity High Fire Intensity
<5% 250 feet 160 feet 130 feet
5-10% 200 feet 120 feet 90 feet
10-20% 120 feet 60 feet 40 feet
20-50% 60 feet 30 feet 20 feet
>50% 40 feet 20 feet 20 feet

Burned log felled across a slope with seeded slender wheatgrass.

 

 

 

 

 

 

With contour log felling, trees are placed directly on the ground and staked in or wedged behind stumps.

Contour Log Felling Illustrations

Illustration showing the spacing of logs across and down a slope.

Illustration showing the placement of a log on a slope.