After the forest fire: Evergreen needles prevent soil erosion

WASHINGTON - Once a raging forest fire is quelled, the next worry is erosion of the landscape. With vegetation destroyed, rain easily washes away the soil, causing large flows of debris and landslides. Erosion endangers sources of drinking water, streams, and roads.

In an unprecedented study, Chris Pannkuk and Peter Robichaud show that scorched evergreen needles can play a key role in preventing erosion after a forest fire. They found that ponderosa pine needles were effective in reducing erosion caused by water running over the soil, and Douglas fir needles were effective in reducing erosion caused by rain hitting and splashing into soil. Their report will appear in Water Resources Research, published by the American Geophysical Union.

These findings can help post-fire rehabilitation teams decide where to apply treatments to reduce erosion. "If you see brown needles in the trees," Robichaud said, "then let's take advantage of Mother Nature and not add any treatments to that area of the forest."

Wildfires usually burn in mosaics, with patches of low, moderate, and high severity. In areas of low or moderate severity, needles from partially burned conifer trees fall to the ground within a few months after the fire. Robichaud noticed that needle cover seemed to reduce erosion on forest soils after a fire. Since no one had formally studied this effect, he and Pannkuk used an artificial rain laboratory at the U.S. Department of Agriculture's Forestry Science Laboratory in Moscow, Idaho, to see how much burnt needles could reduce erosion.

They filled four-meter by one-meter [13-foot by 3-foot] boxes, set at a 22-degree slope, with soil taken from burnt forests. After covering the soil with various amounts of scorched ponderosa pine and Douglas fir needles, they applied artificial rain for 25 minutes at an intensity that would simulate 34 millimeters [1.3 inches] of rain per hour. During each test, they also introduced a stream of water at the top of the box to simulate overland water flow.

The researchers collected and analyzed run-off soil and water from the boxes. They found that a 50 percent ground cover of Douglas fir needles reduced water flow erosion by 20 percent and rain-induced erosion by 80 percent. A 50 percent ground cover of ponderosa pine needles reduced water flow erosion by 40 percent and rain-induced erosion by 60 percent.

Robichaud, who has been studying and modeling erosion after prescribed and wildfire for 13 years, directs several treatment effectiveness projects in California, Colorado, Idaho, Montana, Nevada, and Washington. Pannkuk, who worked with Robichaud as a post-doctorate on this project, is currently a natural resources consultant.

Erosion Control Becomes New Focus after Wildfires

As the season begins to turn over to winter, the threat of wildfires finally diminishes, and wildfire fighters in most of the United States are released into their off-season activities. However, after a particularly large fire season, the threat of fires are replaced with the next threat in the process: extreme soil erosion.

The Burned Area Emergency Response team, or BAER, now becomes a key player in analyzing soil damage and devising ways to prevent erosion. Teams from all over the nation fly into fire areas in order to estimate rehabilitation costs and begin the process. BAER?EUR??,,????'???s rehabilitation abilities include installing water or erosion-control devices, planting, installing temporary barriers and warning signs, replacing minor safety-related facilities, installing drainage features on roads and trails, and removing safety hazards, according to nctimes.com.

However, BAER?EUR??,,????'???s abilities do not extend to replanting commercial forests or grass for forage, excavating and interpreting cultural sites, replacing pasture fences, interpretive signs, buildings, and corrals, repairing roads damaged by floods after fires, monitoring fire effects, and treating pr-existing noxious weeds.

Among the many areas damaged by fire this year, BAER is facing a challenge in Southern California.

?EUR??,,????'??With the sheer number of acres burned, rehabilitation from these fires will be the first of its kind in many ways,?EUR??,,????'?? said Matt Mathes, acting regional BAER information officer, according to nctimes.com. ?EUR??,,????'??The skill and scale of the effort are unprecedented.?EUR??,,????'??

Teams including hydrologists, soil scientists, engineers, biologists, silviculturalists, archaeologists, and range conservationists, among other professions, are examining satellite photos and analyzing on-site situations to assess the condition of the several hundred thousand acres affected by the recent fires.

The teams are working to protect residents from mud slides and flooding by installing temporary barriers of hay bales, fiber rolls, straw matting, sandbags, gravel bags and seeds, reported nctimes.com. Silt fences and hay bales are the most effective erosion control when placed following the slope of the terrain, experts say. But the rain will erode soils easily, as they are slippery from the effects of fire.

Because BAER teams and local officials are concerned about mudflows affecting the local homes, they will maintain roads, clear drainage channels and culverts, and post warnings for flash floods, said nctimes.com.

BAER teams will make case-to-case recommendations about re-seeding as an erosion-control treatment, as native plant species could actually be hindered in some areas. Teams will also apply straw mulch aerially and by hand to prevent runoff.

BAER teams were also called in to the Cascade Springs landscape in Utah to help rehabilitate the area after a prescribed fire gone wild burned 7800 acres this summer. Three helicopters are dropping up to 110 tons of straw daily, and seeding from a 60,000-pound supply bucket, according to newsnet.byu.edu. A total of 644 acres of land will be mulched and 1347 acres will be seeded by the end of the project.

Initial erosion control applications are like band-aids on damaged areas. Depending on the type of landscape that existed before a fire, areas can take up to hundreds of years to fully grow back. However, concentrated efforts to reduce soil runoff can help protect local homes and help jump-start growth in a damaged area.

Certain seed mixes may be recommended for different areas. Contact the closest BAER location to you for detailed information.

BAER recommend replanting the following in Southern California burn areas.

• For a steep slope where the soil is burned, seed and lightly mulch soil (preferably hydro-mulching).
• For a steep slope where the soil is not burned, lightly mulch (preferably hydro-mulching).
• On a rolling slope or flat area that was shrubland before burning, do nothing
• Rolling slopes or flat areas that were annual grassland or weed patches should be seeded with native seeds

Seed mixes (to be used sparingly)

BELOW 2500 FEET IN ELEVATION

• California Sagebrush
• Flat-topped Buckwheat
• Deerweed
• Dwarf lupine
• California brittlebursh

• Manzanita
• Arroyo lupine
• Toyon
• California Brome
• Wild lilac
• Blue wild rye

• Willow whips
• Mulefat
• Mugwort
• Creeping wild rye
• Trailing Blackbery

Call the Burn Area Emergency Response Team at 858-879-2535 for more information.

Application of straw to prevent erosion control (graphic provided courtesy of Natural Resources Conservation Service.)

Contour Log Terrace. These barriers are an effective, first-year treatment for hydrophobic soils, low ground cover density, and severely burned areas (graphic courtesy of Natural Resources Conservation Service.)

Silt fences are suitable for areas where runoff is in the form of "sheet flow" (graphic courtesy of Natural Resources Conservation Service).

Water bar construction for forest or ranch roads with little or no traffic. Specifications are average and may be adjusted to conditions.

• Bank tie-in point; cut 6 inches to 1 foot into the roadbed.
• Cross drain berm height 1 to 2 feet above the roadbed.
• Drain outlet cut 8 inches to 16 inches into the roadbed.
• Angle drain 30 to 45 degrees downgrade with road centerline.
• Up to 2 feet in height.
• Depth to 18 inches.
• 3 to 4 feet.