March 1, 2004 | General

Processing Wood Residuals In The Southwest

Robert Rynk
BioCycle March 2004, Vol. 45, No. 3, p. 28

Before the salt cedars took hold, the flood plains of the Rio Grande River in the Southwestern United States were dominated by cottonwood/willow forests and open grasslands. Now salt cedars and other invasive trees are displacing these native species, deteriorating habitats for wildlife, depleting water and increasing the fire risk. It is an important and immediate ecological problem. Salt cedars thrive in a wide range of conditions so they are prevalent across the arid west. However, they are a particular threat to the riparian areas and flood plains in the Southwest.
Salt cedars are difficult to eradicate. They are extremely hardy and tend to out-compete native plants. Fortunately, restoring the landscape to its natural condition has become a priority in the Southwest. Numerous public agencies and land managers have embarked on projects to remove these persistent nonnative plants in hopes of reestablishing native habitats. The most successful approaches involve mechanically removing the trees. The task requires the skills and equipment of forestry and wood residuals processing companies and is especially suited to mobile grinding operations. As an example, this article profiles habitat restoration projects being conducted in the Southwest by Racher Resource Management (RRM), a natural resource management company based in Corona, New Mexico. It also discusses the need to find beneficial uses for the biomass that is being generated from these types of projects.
The salt cedar, or tamarisk, is a type of deciduous shrub or small tree that spreads rapidly and grows to heights of five to 30 ft. Species of salt cedars are native to parts of Western Europe, the Mediterranean region, China and India. They were first brought to the U.S. in the 1820s as an ornamental nursery plant. Later in that century, it was reportedly used in the West to stabilize soil along stream banks.
Since its introduction, the salt cedar has managed to colonize wide areas of the natural habitat in the U.S. and Canada. It can adapt to a variety of conditions, including drought. It is difficult to kill, reproduces rapidly and changes the soil conditions to the detriment of other plants. In addition to its thirst for water, the stems and leaves of salt cedars secrete salt, which alters the soil condition and inhibits the growth of other plants. According to the U.S. Department of the Interior and the USDA, salt cedars have infested over 1.6 million acres of stream banks and wetlands in the western U.S. The extensive stands of salt cedars impede water flow and can contribute to flooding. Fallen leaves and mass of branches add fuel for wildfires.
The competitive advantage of salt cedars is partially due to its root system. It has a deep and extensive network of roots that allows it to survive under drought conditions and to pilfer water from other users. A large tree can consume 200 gallons of water per day. A stand of trees can lower groundwater levels and desiccate marshes.
Brent Racher, a natural resource specialist and manger/principal owner of RRM, explains that although the salt cedars present serious natural habitat and fire threats, the biggest force driving its removal has been water conservation. Primarily, it is the salt cedars’ propensity to consume large amounts of water that has made it a target for control in arid regions. Much of the funding for the salt cedar removal comes from water authorities and soil and water conservation districts.
The federally-funded “Collaborative Forest Restoration Program” is a pilot project, being tested in New Mexico, that is examining approaches to improve forest health and reestablishing native forest habitats. The program also seeks to support local economic development by promoting uses of the material being removed from the forest, like small diameter trees. Racher expects this program will be expanded nationwide in several years.
While the spread of salt cedars is a big problem in itself, it is a just one component of broader ecological changes that are taking place. For instance, in addition to salt cedars, a number of invasive plants and animals, including nonnative Russian olive trees, are displacing native species in the Southwest. Climate patterns, fire suppression, management of waterways and floods, urbanization, agriculture and habitat loss are contributing to changes in natural ecosystems in the Southwest and other regions. Flood control has curtailed the historic behavior of river systems, eliminating the regular cycles of soil saturation, nutrient distribution and channel migration to which native species have adapted. It has been suggested that this is contributing to the proliferation of salt cedar, Russian olive and other invasive species. Thus, eradication of these invaders may not be possible without addressing the underlying ecological changes. In the meantime, the strategy is to restore native ecosystems by controlling the salt cedars and other invasive species, not necessarily eliminating them.
Numerous land management agencies and private landowners in the Southwest have made restoration of the native ecosystem a priority. RRM has taken on more than a few of those projects. Both public agencies and private landowners have hired RRM to remove salt cedars and other invasive species from forested areas, primarily areas within the historical flood plains of the region’s rivers. RRM has worked to clear salt cedars and other invasive plants in several southwestern river corridors including the Rio Grande, Colorado, Pecos, Canadian and Arkansas. For instance, salt cedars are a serious threat to the ecosystem along the middle stretch of the Rio Grande that runs through New Mexico, the forested flood plain, known regionally as the “bosque.”
The historical riparian forests in these cases range from 100 yards to over a mile wide. The terrain varies from narrow rights-of-ways along river corridors (surrounded by agricultural land and urban/population centers) to lush riparian areas surrounded by desert ecosystems. Where the terrain and land ownership allow, the river corridors constitute the prime agricultural land, the best wildlife habitat, and/or the most dynamic ecosystem.
Ordinarily RRM specializes in ecological restoration projects through controlled burning. However, in response to the demand, the company has expanded its salt cedar control service, which requires a more mechanical, equipment-oriented approach. “We basically start from one end of the area to be treated, remove the target vegetation and then come in with a grinder to chip the biomass,” explains Racher. RRM removes whatever trees and vegetation are necessary to meet the client’s objectives, whether that is specifically salt cedar and Russian olive control or other reasons. According to Racher, most private landowners seek to reduce fire risks, improve the land for livestock grazing or improve the aesthetics. On public lands habitat restoration, water conservation and fuel reduction are usually the goals. Some projects involve clearing burned areas of standing trees.
Eliminating salt cedars is not easy. Burning is only effective in stunting the development of mature plants. It cannot be used as a control by itself. Several herbicides are effective but spraying is often constrained by the possible impacts on other vegetation, wildlife and the environment. Biological controls are just beginning to be explored. Mechanical methods – removing the trees by cutting, plowing and pulling – are the most reliable controls if the root system also can be destroyed. To stand a chance of killing the tree, roots must be removed or treated when the above ground part of the tree is removed. Options include pulling or bulldozing up the roots with the tree, deep plowing of the soil after cutting and treating the cut stump with a root-killing herbicide. Obviously, mechanical control is a laborious approach and depends on how much the soil and surrounding vegetation can be disturbed.
RRM primarily uses a mechanical approach. Trees are literally pulled out of the ground using a grapple-like bucket on an excavator, which RRM calls an “extractor.” After the extractor pulls out the tree and shakes off whatever soil it can, the tree is placed at the end of a windrow of stockpiled trees and brush. The operator continues on to the next target tree pulling and windrowing until the entire area is cleared. In places where the excavator cannot be used, such as in unstable soil and river banks, trees are cut close to the ground with chainsaws and the stumps are brushed with herbicide to kill the root system.
Usually, the grinder comes in after the extractor crew has finished its work. RRM uses a Vermeer mobile track-mounted horizontal feed drum grinder. The grinder tracks along the windrow of extracted trees, fed into the grinder by an excavator or bucket loader with a grapple attachment. Skid steer loaders or front-end loaders are used to clean the site of litter (e.g, brush, branches and limbs) and deliver these materials directly to the grinder. The grinder handles whole trees with the root balls intact. According to Racher, Russian olive trees can have root balls nearly 30 inches wide, the size capacity of the grinder. Because of the horizontal feed, tree length is not a limitation, he points out. In RRM’s work, the grinder produces chips at an average rate of 10 to 15 tons per hour (tph), but can operate as high as 30 to 35 tph. “Some contracts specify the chip size, usually three or four inch-minus,” notes Racher, “but otherwise we keep a four-inch screen on the grinder.”
After clearing, most sites have enough native vegetation to retain a park-like appearance. According to Racher, the native vegetation reestablishes itself quickly and naturally. Replanting is not normally necessary. However, for some projects, such as in burned areas, RRM does replant cottonwood trees. The technique, called “pole planting,” is to auger a planting hole down to the water table, often four to eight feet deep, and place the cottonwood “poles” in the hole. The planted trees then begin to develop roots. The cottonwood poles, typically four to eight inches in diameter and up to 16 ft. long, can be limbs cut from other trees in the surrounding area. However, usually tree nurseries supply the planting stock.
The extensive acres being treated and the large amount of biomass removed produces a huge quantity of wood chips. RRM’s grinder typically works a full-time schedule, eight to ten hours per day, five to six days per week. Because of the remote locations and low populations of many of the areas where RRM works, the chips usually remain on site (sometimes the contract requires it). “In most cases, we spread the chips over the treated areas to improve the site,” explains Racher. “The chips serve as a mulch, hold in the water, add organic matter and help to control erosion. Although there may be higher value uses for the chips, in most cases it is too costly to truck them to processing facilities and markets.” RRM distributes the chips on the treated area with a skid steer, bucket loader or, more frequently, a manure spreader. RRM spreads the chips as evenly as possible, in a two to three inch layer, but also makes sure to cover erosion prone areas like bare slopes and areas torn up by equipment. Some contracts even specify the depth of application. “Some land owners want us to produce a park-like look with a smooth grade and an even layer of chips,” adds Racher. According to his observations, the chips have generally enhanced vegetation growth because they conserve soil moisture. Racher acknowledges that soil nitrogen can be immobilized as the chips decompose but he has not observed that effect yet. Apparently moisture is a more limiting factor to plant growth.
Where the opportunities exist, RRM has delivered chips to off-site users, including a composting facility in Albuquerque. In populated areas, chips have been offered to residents to take freely but the supply still farout strips the uses. Racher expects that current efforts to develop better uses for forest biomass will eventually produce several higher value outlets for the chips and increase the demand for the biomass.
Restoring forests to their natural conditions will continue for years. As a result of salt cedar and Russian olive removal and forest thinning generally, a huge volume of woody biomass will be coming out of the forests in the next ten years, and beyond. Some chipped material should remain in the forests to recycle nutrients, improve the soils and prevent erosion. Vicky Estrada, District Ranger in New Mexico’s Mountainair District, states, “we want to keep at least a portion of the biomass in the forest and disperse it to recycle nutrients in the soil.” However, the large volumes of biomass that need to be removed present opportunities for more economical and sustainable uses. The Forest Service, states, communities and companies are collectively pursuing several viable value-added options for wood being generated from forest restoration activities.
There is currently a plan to develop a biomass-powered electricity generating plant in Estancia, New Mexico. Estancia is a sparsely populated and remote location, far from electric utility customers but near woodland and forested areas that would generate the fuel. The powerplant is expected to come online in two to three years. A groundbreaking is planned for June 2004. Other biomass plants in Albuquerque and Raton, New Mexico are also being developed. The biomass plant in Albuquerque has been constructed and is in the start-up phase.
Biomass fuel is also being considered for a sign manufacturing company located in Mountainair. Through Estrada’s district, the Forest Service is working with the company to develop a process and business that produces signs from low-grade wood products and recycled plastic (see sidebar). The sign company is currently producing signs on an order basis but is planning to expand the operation to a large mass production scale. While wood from salt cedars will not be used for the signs, the company is planning a cogeneration plant that will power and heat the factory with biomass fuel removed from the forests. Again, this facility is sited close to sources of the wood biomass to minimize transportation costs.
The Forest Service has a program called the “Burned Area Emergency Rehabilitation” (BAER) that seeks to quickly address the threats that remain in the aftermath of a wildfire, particularly from runoff and erosion. The Forest Service in the Southwest region has just started to investigate use of wood mulch as an erosion control measure under the BAER program. The mulch would be applied to burned areas that are susceptible to erosion. RRM is contributing chipped wood mulch to the program. In this case, RRM first piles the chipped material and allows the piles to self-heat for several days in order to decompose the fine particles and destroy weed seeds. Estrada sees this application as a general trend in forested areas. “Land managers are increasingly using chipped forest biomass for erosion control in gullies and drainage unburned as well as burned areas.” The chipped material has an advantage over slash (tree limbs and tops) in that the material breaks down and cycles into the soil more quickly.
The use of wood mulch and compost for vegetation establishment and erosion control in highway construction is a promising application. According to Racher, there is a lot of highway work taking place and much of it is in remote locations near the biomass sources. Although promising, highway projects in New Mexico have not yet embraced this practice.
As Racher sees it, forest restoration in the Southwest will be a perpetual effort. “Follow-up and maintenance activities will be critical even after the salt cedars and other invasive plants are removed.” In addition, the task has really just started. Racher estimates that the areas treated for salt cedars amount to less than ten percent of the 99,000 acres needing treatment. “So far the problem has been attacked in patches. There has not yet been a concerted effort to attack the problem for an entire river system.” The situation may be changing, however. The U.S. government’s National Invasive Species Council (a cabinet level group that includes the departments of the Interior, Agriculture and Commerce) recently announced a strategic initiative aimed at controlling salt cedars in the Southwest across political and geographic boundaries. A three-day conference focused on this issue will be held in Albuquerque from March 31 to April 2 as part of the initiative.
Whatever measures are taken to get a handle on the salt cedar problem, it will obviously take a long time and will generate a lot of biomass. Fortunately, uses for the biomass are being explored and developed. Estrada believes that the solutions that are being pursued also will bring economic activity and benefits to the economically beleaguered communities of the Southwest.
P&M SIGNS, INC. of Mountainair, New Mexico is embarking on a venture to manufacture signs from a composite material made from recycled plastic plus low-grade wood generated from ecological restoration activities. In addition, the company plans to power the manufacturing process with energy derived from forest biomass, like salt cedars. The company provides an excellent example of business built on sustainable concepts, both environmental and economic. P&M currently operates a facility that produces a variety of sign products primarily for state and federal agencies. Its products include highway signs, historical markers and signs that identify natural features and parks. The company makes signs from a variety of materials in its existing facility. However, it is expecting that the new composite product will become a niche that stimulates the company’s growth. A pilot-scale facility is in place, producing composite signs for testing and special orders. The company has successfully developed the composite sign product and the process. Engineering designs and specifications have been drawn up for a full-scale manufacturing facility. P&M is currently lining up funding to bring it to reality.
In part, the motivation to develop the composite product was to find a use for the abundant wood from juniper trees. In a story similar to the salt cedar, juniper and pinion trees have proliferated and altered natural grassland ecosystems, largely because of changes in land management practices and fire suppression. Efforts are underway to remove these trees and restore the natural landscapes. However, a glut of wood products is being created that are not suitable for timber. Similarly, efforts to reduce fuel levels in overstocked forests (also due to fire suppression) have generated an abundance of small diameter trees. Federal agencies have established incentives to develop uses for these low-grade wood sources. P&M’s owner, Phil Archuletta, recognized the opportunities and started to investigate the composite sign product. (Before starting P&M, Archuletta acquired over 30 years of experience providing signs to public agencies and even helped to develop sign specifications for the Forest Service.)
Archuletta developed the composite sign products and process in partnership with the U.S. Forest Products Laboratory (FPL). In fact, the patents that developed are held jointly by P&M and FPL. The product combines wood particles with #2 HDPE (high density polyethelene) derived from milk containers. The wood particles are shredded in successive stages to a 1/8-inch particle size, screened to remove soil particles, and kiln dried. Plastic bottles are shredded on site. Then both materials are coextruded to produce the composite panels. Archuletta explains, “Our hope is that public agencies will use this composite material to replace signs made from less sustainable wood materials like redwood. Our composite panels perform very well. They are durable. They can take nails well. You can cut them, route them, shape them and bend them. They have been successfully tested by the Forest Products Lab and in places like the Grand Canyon.”
A variety of woods have been successfully tested for the composite signs, including pinion pine and ponderossa pine. P&M settled on juniper because of its abundance, availability and durability. As Archuletta explains, “Juniper naturally repels insects and, unlike plywood, porcupines won’t touch it.” Porcupines are a particular threat to wooden signs in natural areas. P&M’s rural location gives it access to “more juniper than we could ever use,” as Archuletta notes. In addition, P&M’s facility is situated next to a rail line and close to a highway, making access to raw wood products that much better. P&M obtains plastic bottles in compressed bales from a recycling facility in Albuquerque. In addition, it also has an active collection program among the local residents and school students.
For full—scale production, P&M plans to take the sustainability concept further by installing a biomass-fueled cogeneration facility. The cogeneration plant will power the manufacturing process providing steam, heat for kiln dryers and electricity to power the extruder. The biomass will be a mix of wood-based residuals, like salt cedar, obtained from regional land management activities. In the proposed process, the biomass will be gasified and then combusted to create steam. The steam, in turn, will drive turbines to generate electricity. The remaining energy will be captured for heat.
With this new venture, Archuletta is interested in promoting both sustainable land management and economic development. He expects it to provide much needed jobs and economic stimulus to Mountainair, a community of less than 1,200 residents. At present, the sign company employs 22 people. Archuletta expects that number to increase to 65 once the composite products facility is running at full-scale.

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