In revegetation, everything begins with the soil—usually poor soil.
Soils may become degraded during the construction of buildings, roadside projects, or mining or landfill operations, or because of overgrazing or deforestation. They lose their topsoil, usually the top 2- to 8-inch layer of the soil, where the most important nutrients lie. In addition to sand, stone, and clay, topsoil contains decayed plant and animal matter, bacteria, fungi, algae, insects, earthworms, and nematodes.
This is where plants generally concentrate their roots, which reach out and stabilize the soil. When the plants and their roots are removed, especially on slopes, the topsoil is the first thing to erode.
The subsoils are inferior. Sandy soils contain so much air between the particles that any microbes in the soil consume organic matter very quickly. Without organic matter, soil particles don’t stick together and form crumb structures, and water drains into the subsoil too quickly.
Compacted and clay soils contain so little air that they are generally low in both organic matter and microbes. Plant roots become stunted because it is too hard for them to push their way through the soil. Because water drains through them slowly, it can completely fill the pore spaces, waterlogging the soil.
Acidic and alkaline soils prevent nutrients such as nitrogen, phosphorus, potassium, iron, zinc, copper, and manganese from dissolving in water. As a result, nutrients can’t be readily absorbed by plants’ roots.
Soils may be contaminated by chemicals, stripped of nutrients by overtillage and inadequate soil management, or salinated by irrigation water. Degraded land often absorbs less water, which can cause or worsen flooding.
All soil problems can be improved by various methods to varying degrees.
Incorporating compost—the partially decomposed remains of soil organisms and plant life—helps replace the topsoil. Compost buffers the soil, which neutralizes both acid and alkaline soils. It improves soil structure by binding clusters of soil particles, called aggregates, and making the soil less likely to erode. These aggregates have both large and small pore spaces, which moderate the flows of air and water and slow down the consumption of the organic matter by the organisms in the soil.
Compost contains macro- and micronutrients that feed the organisms in the soil, such as bacteria, fungi, nematodes, insects, and earthworms, which keep the soil well-aerated. The excretions from these organisms convert organic matter and soil minerals into vitamins, hormones, and nutrients that plants need to grow. The excretions improve the soil structure as well.
Mulch is a layer of a material on top of the soil. It can be organic, such as wood chips, straw, and even compost, or inorganic, such as stones, brick chips, and plastic. It may include soil amendments and/or seed. It can be applied manually, by blower truck, and by hydroseeding equipment. Mulch protects the soil from erosion, reduces compaction from heavy rains, conserves moisture, moderates the soil temperature, and prevents weed growth. As organic mulches decompose, they provide organic matter to the soil, which improves root growth, increases water infiltration, and improves the water-holding capacity of the soil.
When soils are unhealthy, not simply poor, soil amendments provide additional help. Some soil amendments are simple. They include sphagnum peat moss, lime, sulfur, gypsum, and builder’s sand.
The slope before the 2014 revegetation
On the other hand, some soil amendments are ingenious and hi-tech. For example, BioSol, from Rocky Mountain Bio Products in Denver, CO, is a byproduct of the manufacture of penicillin. When raw materials such as soybean meal, cottonseed meal, sucrose, lactose, trace elements, and vitamins are fermented under constant sterile conditions, they produce a fungal mass, or mycelium. The penicillin is extracted and the remaining mycelium is dried and granulated, and sold as BioSol.
The high organic content in BioSol stimulates root development and microorganisms, such as bacteria, which provide quality micro- and macronutrients for plants. In addition, because some of the bacteria fix, or convert, nitrogen into compounds that are available to plants, the risk of nitrate leaching is very low.
The Parker slope after project completion
Mycorrhizae, which Rocky Mountain supplies as well, improve plants’ ability to absorb water and nutrients from the soil, enhance their health and vigor, and increase their resistance to stress and diseases. They also improve the phytoremediation of sites contaminated by petroleum and heavy metal, according to Texas A&M University.
PermaMatrix, from Sunmark Environmental and Sunmark Seeds in Portland, OR, contains biochar, organics, micro-organisms, beneficial fungi, water-holding materials, and many other soil-like components.
Biochar is a charcoal used as a soil amendment. It’s a product of pyrolysis, which occurs when biomass such as crop residues, nut shells, fruit pits, animal manures, and yard, food, and forestry wastes, decompose at the temperature of 550°C in the absence of oxygen. Because there’s no oxygen, the biomass doesn’t combust. Instead, the chemical compounds that make it up thermally decompose into combustible gases and charcoal, according to the USDA Agricultural Research Service.
Biochar does not decompose with time. It provides nutrients, increases water absorption, and minimizes the leaching of nutrients into the groundwater. It improves the physical and chemical properties of the soil and provides bioremediation by absorbing contaminants, including inorganic and organic pollutants, which improves water quality. It also helps with carbon sequestration, or long-term storage, in the soil.
Once the soil has been amended, it’s ready for planting. The seed is crucial to the success of any revegetation project.
For hundreds of years, immigrants, beginning with the first settlers in the United States, brought seeds with them from their homelands. They planted them as they moved westward across the country, for food crops, livestock forage, windbreaks, landscaping, and medicine.
They also used the seeds to control erosion. Many of the introduced seeds were readily available, inexpensive, fast growing, and aggressive—exactly what was needed for quick and effective revegetation. These introduced species spread virtually uncontrolled and have been causing major environmental problems across the country. They outcompete native species for water, light, and soil nutrients, which degrades the habitat, causing the loss of biodiversity and native ecosystems. On farmland, they can injure or kill livestock. They also increase the risk of wildfires.
Ironically, they can also result in erosion, which causes the loss of topsoil and the land under it, especially on slopes. The sediment, which may contain pollutants, clogs rivers and streams, and causes a decline in fish and other populations.
Using native plants and trees, which occur naturally in a given habitat, to revegetate an area is ultimately more effective and efficient than using non-natives because nature is doing the long-term work. Native plant and tree species are adapted to the soils, weather, and even wildfires in their area. They’re diverse, so if one species fails, others are more likely to survive. They support biological diversity because they’ve evolved with local wildlife and they provide it with food and shelter. At the same time, native soil organisms nourish native vegetation, and native predators feed on pests that attack it.
The plants may be applied as seed, young plants, or stakes, as well as plants that were salvaged from the site either before the site was disturbed or at the beginning of the project.
The two revegetation projects below illustrate what can be accomplished by improving the soil and planting native seed.
Parker, CO
During one week in September 2013, approximately 15 inches of rainfall soaked the town of Parker, CO.
Among the damage was a slope that washed out—one that had been revegetated with grass seed and erosion control blankets some six years before.
“It seems hard to revegetate out there,” says Rick Schmitt, manager of Down To Earth Compliance (DTEC) in Aurora, CO. “This is an area of the town that has struggled with revegetation on other slopes in the past as well.”
Schmitt oversaw the project to revegetate the slope a second time, a year after the 2013 washout, and coordinated with others working on other projects on the site.
DTEC, whose services include stormwater management, sediment and erosion control, and revegetation, handled the installation. The company has always prided itself on doing the highest quality work, says Schmitt. Back in 2005, management teamed up with HBA of Metro Denver to train employees in the history of the Clean Water Act and federal and state regulations regarding stormwater discharges.
The original revegetation project had been necessary because a commercial building project had required regrading of the slope. The slope, which is 3:1 and at least 100 feet high, has an area of approximately 2 acres. The soil, a sandy loam with a high pH and high salts but only 4.4% organic matter, had been completely disturbed. By 2013, eight years after the first project, the vegetation consisted of clumps of grass scattered on the slope. When the rain hit, it washed out.
The second revegetation project took place in June 2014 and took less than a week. Drill seeding wasn’t possible because of the steepness
of the slope, and the option to completely redo the project wasn’t efficient or cost effective.
“There was enough vegetation that we didn’t want to start over,” says Schmitt. “Usually it takes about three years for the vegetation to get established. We didn’t want to reset the clock.”
Instead, DTEC used a compost blanket injected with seed that was approved by the town of Parker, from Arkansas Valley Seed in Denver. They also used the soil amendments BioSol Forte and mycorrhizae fr om Rocky Mountain Bio Products in Denver.
“We’ve used BioSol on numerous occasions in the past, probably since 2008,” he says. “We have a good relationship with Tom [Bowman, of Rocky Mountain Bio Products]. We trust his recommendations, and we’ve had success with the product.”
At the beginning of the project, DTEC reestablished the straw wattles that were still in place from the 2005 project. The subcontractor, Bedrock Slingers of Loveland, CO, used a blower truck to fill in the bare spots on the slope with the seed, compost, and soil amendment mixture.
The biggest challenge was finishing the project before the summer heat began. “The optimal times to seed are in the spring, so the seeds don’t sit in the heat, and in the fall,” says Schmitt.
They waited until June, while another company finished grading the slope and installing the concrete drain pan at the bottom of the slope.
“It was the best we could do,” he says. “We couldn’t have left the slope exposed ’till fall.”
Nevertheless, one year later, the growth was lush. Getting water to the seed regularly was an important consideration, he says. It was a wet year and the slope was irrigated. The owner of the project used a combination of permanent and temporary irrigation to aid in revegetation.
The only maintenance that’s been required has been cleaning up the drain pan to catch soil runoff once or twice.
“The results are absolutely outstanding,” says Schmitt. “There’s grass all over the place.”
As they built the wall, workers planted bare root plants and stakes. They used ermaMatrix on the roots of each plant.
Canoe Bay Project, OR
This was a two-step project. The first step was amending the soil, planting native seed and plants, and stabilizing the slope. The second was hydroseeding the area with additional soil amendment and seed.
For decades, the banks surrounding Canoe Bay on the Columbia River were the dump at the end of the road. Then, in 1996, the waters of the bay rose above them. They flooded businesses and homes and caused serious erosion to the slope, undermining the land above.
“The owner of the property, Inland Sea Maritime Group, had done a lot of things to try to protect the bank, unsuccessfully. Then he did some dredging of the marina and found contamination,” says Ron McPherson, a principal with EnvirolokWest in Portland.
The majority of the contamination was at the northern end of the property, where approximately 80 feet were contaminated with PCBs, metals, polycyclic aromatic hydrocarbons, and tributyltin. In the southern section, there were concrete and asphalt chunks, as well as a stormwater outfall conveying runoff from the parking lot above. In addition, the site was covered with invasive plant species, especially Himalayan blackberry.
One option was for the owner to remove all the contamination, which was not cost effective and wouldn’t have repaired the erosion damage or allowed for revegetation. Another was to use riprap. Riprap wouldn’t cap the contamination or hold vegetation; in addition, the Army Corps of Engineers had used it earlier, and the boulders had slid to the bottom of the slope. A third option was to build a wall using the Envirolok system and vegetate it with native plants and seeds.
“It totally made sense to use the Envirolok system,” says McPherson, who oversaw the project to control the erosion, cap the contaminated area, and revegetate the bank on the property.
The system consists of rows of non-biodegradable polypropylene bags tied together to create a stable cap over the soils. The bags contain a growing media that supports vegetation and filters contaminated water, preventing further leaching of contaminated materials into the bay.
The vegetation is an integral part of the system, he says. “The magic is that we plant between the layers of bags and the roots grow right into the bags—in some cases, into five or six bags.”
The project used native seeds and PermaMatrix biotic soil amendment from Sunmark Environmental in Portland. “Sunmark manufactures and supplies PermaMatrix, which is very effective for plant growth and revitalizing the soil in eroded areas,” he says.
The completed project
PBS Engineering and Environmental Inc. in Portland, OR, provided the planning, engineering, and inspections during and after the project, and also obtained all the required permits. The permitting process involved the Army Corps of Engineers, the Oregon Department of Environmental Quality (DEQ), the Oregon Department of State Lands, the city of Portland, and other federal agencies that deal with endangered species.
The project took place in the fall of 2013. Big Mountain Construction in Brightwood, OR, the general contractor for the project, built the cap and assisted with the design.
“The contamination portion of this project required a high level of experience and ingenuity,” says McPherson. “With limited equipment and difficult access, the project was completed on time and on budget with no interruption to the business located on the property.”
The general slope design was 2:1, but to achieve the natural look of the riverbank Big Mountain followed the existing slopes. In a few cases the bank was almost vertical.
The project required more than 10,000 Envirolok bags. Each one is about 17 inches wide and 26 inches long, and was filled with 80% sand, 15% topsoil, and 5% compost.
Crews began at the northern part of the slope, which averaged approximately 25 feet high but reached 40 feet high in places. They installed silt fence at the bottom and cleared slope of the debris, brush, and invasive vegetation.
They dug a trench 2 feet below and approximately 30 feet behind the water line to prevent scour. They used the boulders that had tumbled down the slope after the previous riprap attempt for the foundation of the wall and began laying down the first row of bags.
“Sometimes there was water in the trench,” says McPherson, “but after the first row of bags went down, the installers were dry because they were standing on the bags.”
Big Mountain crews worked their way to the top, placing the bags up and across the natural slope and anchoring them into the slope with duckbill anchors for stabilization. They did a large part by hand because of the limits on the equipment they were allowed to take in.
They used backfill from the Columbia River mixed with topsoil and compost in some areas of the slope. There was no need to install drainage, because catch basins and other drainage were located nearby.
As they built the wall, they planted bare root plants and stakes from Watershed Garden Works Native Plant Nursery in Longview, WA. They placed PermaMatrix, Sunmark’s soil amendment that contains biochar, on the roots of each plant.
Big Mountain used almost every plant imaginable that’s native to that area, says McPherson. “We planted heavily: wildflowers, grasses, woody plants, and willows. There are over 14,000 native plants in that wall.”
Sunmark designed the plant selection and the seed mixes. A native wetlands seed mix was chosen to tolerate the tides and flooding in the lower areas, and a native dryland mix for the upper slopes.
“Both were extremely successful,” says McPherson.
At the base of the wall and extending about 15 feet toward the water, Big Mountain built a sand filter to prevent any contaminants from reaching the bay. It includes several layers of sand and rock with a layer of geofabric to stop the material from eroding.
South of this section of the slope was the gangway area for the Schooner Creek Boat Works. Just south of the gangway area, a 200-foot section of eroded slope ended at the property line. The slope included a stormwater outfall that contained runoff from the parking lot above.
In this section, Big Mountain crews built another wall of Envirolok bags planted with native plants. They also built an Envirolok berm under the outfall and vegetated it with native seeds and plants to filter the water draining from it and to prevent erosion below.
Last, they hydroseeded all sections of the slope with seed and PermaMatrix, including the disturbed soils around the walls. The entire project was completed in less than four months.
The property owner, Inland Sea Maritime Group, is required to maintain the slope for five years, mostly to keep the invasive species from growing back, says McPherson. So far, almost none has, although some seeds are coming in on the wind.
The city and the DEQ required native plants to provide a 90% coverage of all Envirolok slopes within one year. All the agencies signed off on the coverage, and the DEQ provided a “no further action” letter for the contamination after only six months.
“The project was masterfully done,” says McPherson. “We had a great design group and a great contractor, and we’ve had really good success with the vegetation. We’re providing habitat for a lot of endangered and native species: fish, birds, butterflies, deer, and beaver.”