SDSU

Soil Ecology and Restoration Group

last update March 17, 1995

Restoration in the California Desert
Vertical mulch for site protection
and revegetation

Prepared for the
California Department of Transportation
as part of the Desert Plants Project
November 1994

David A. Bainbridge
Biology Department
San Diego State University
San Diego, California 92182

  1. Introduction

    Erosion control and revegetation of bare slopes and large sandy areas resulting from construction, vehicle operation, or recreational activities can be difficult and expensive. Options include erosion control fabric; terracing; trenching or ridging the contour; hydromulching (with wood fiber or straw); and wattling (placing vertical or horizontal layers of brush or vegetation into the soil) to stabilize slopes for seeding and container planting. Hydromulched, tackified, or crimped straw has often been used as an erosion control barrier and seed cover.

    These methods have a poor record in dry climates. The mechanical treatments are expensive, leave potentially permanent patterns on the landscape, and are ill-suited for restoration and protection of natural areas. Hydromulch often provides sufficient moisture to germinate seed, but seedlings dry out and die in these arid environments.

    Vertical mulching, or placing straw, sticks, or brush upright in the soil may be effective for treating these problem areas. This method provides many benefits, including: slowing water movement; providing open channels for water penetration into the deep soil; safe sites for seeds to catch and sprout; wind breaks to trap seeds and dust; shade and cover for seedlings; and providing a source of below-ground organic matter to help return the soil ecosystem to health. Experiments have shown that vertical mulch can increase soil moisture storage substantially (>20%, Fairbourn, 1975), which may be critical in the desert. Mini-dams are particularly important to reduce water velocity and erosion in channels and rills.

    Several materials can be used for vertical mulch, including: broom corn, straw, brush and reeds. The best choice for a given site will depend on availability and cost of materials, project demand for aesthetics, integration of seeding and container planting, and severity of erosion and land stability problems.

  2. Broom corn

    Broom corn (Sorghum vulgare) is a promising vertical mulch. The stem is easily inserted into a hole or slot in the ground (drilled, punched, or dug) and the multi-branched top is an effective wind break and erosion trap (figure). Overall lengths range from 18-24 inches. The plants are harvested in flower (Kirby, 1963) and are further processed to eliminate immature seeds, so the material is clean and unlikely to have viable seeds. It is more expensive than straw, but the fraction of broom corn that doesn't meet broom specifications could be reasonably inexpensive if a revegetation market is developed.

    Several people are needed for an effective installation team. Punches, shovels, or drills are used to make placement holes or slots. Shovels can be used to open a slit in a gully to place a dam of broom corn (extending 6-12 inches above ground) which is braced with horizontal bamboo crossbars. Soil is then tamped around the stem (figure).

    Tests underway at Cuyumaca State Park are comparing the benefits of broom corn with coir netting (coconut fiber), bamboo, and brush for erosion control. Extensive testing is also planned for wind erosion control and revegetation at Red Rock Canyon State Park.

    A 100 pound bale should treat 2-4 acres with 1000 stalks per acre. A bale would also create 60-70, two foot wide check dams. Cost are expected to run about $50 per acre for material and $50-150 per acre for labor.

  3. Vertical straw methods

    Rice (Oryza sativa) straw has been used in both coastal and desert sites. Rice straw has a high silica content and decomposes slowly even in moist soils. Rice straw is preferred over other straws as it is less likely to carry weed seeds adapted to dry areas (OWPS, 1975). However, baled or bound straw of any species may contain many seeds unless it is specifically harvested for conservation or cleaned after harvest. Wheat, oat, or rye straw, can also be used but only clean bright straw is recommended.

    Although most straw is now baled, it could easily be picked up in a binder-reaper which ties straw bundles with jute or sisal twine. This would reduce field costs and speed installation. Cost of hand placing straw bundles 1-2 feet apart was $260 per acre (1987) at 2,000 per lbs acre. Rice straw cost would be about $30-40 ton, for an estimated total installion cost today of $340 per acre (figure).

  4. Brush

    Brush has a long history of use in traditional agriculture in both water diversion structures and in field crop protection (Wilken, 1987; Schiechtl, 1980; SCS, 1992). Placing the stems vertically can improve effectiveness over laying them horizontally on the surface in some cases.

  5. Reeds

    Reeds have been used for dune stabilization in several areas. Reed fences (10 cm buried, 40 cm exposed) have been very effective as wind fences in desert areas with shifting sands (Tag El Din, 1986). Reed bundles would be effective and as long-lived as vertical mulch. Reed is not readily available on the market in California, but rushes (Juncus spp.), reeds (Phragamites spp.), and sedges (Scirpus spp.) would be appropriate if available as part of other operations on or near the site. Reeds are very durable and would persist many years. Reed roof thatch has a typical life of 75-100 years in the more humid regions of France (Walshe and Miller, 1992).

  6. Summary

    Vertical mulching, or placing straw, sticks, or brush upright in the soil is one of the best methods for protecting denuded areas and encouraging plant establishment. This treatment increases water capture and retention; provides safe sites for seeds and seedlings; traps blowing dust; slows water erosion; and provides moisture and a source of organic matter to the below-ground soil ecosystem. Vertical mulch can discourage traffic, walking or driving, by providing a visual and physical barrier.

  7. References

Fairbourn, M.L. 1975. Field evaluation of microwatersheds and vertical mulch systems. pp. 233-243. In Frasier, G.W. ed. Water Harvesting Symposium, Phoenix Arizona. Agricultural Research Service ARS W-22, Berkeley, CA

Faull, M. 1987. Desert scrub restoration 1986/87. Red Rock Canyon State Park: Project Status Report. Red Rock Canyon State Park 41 p.

Ferreira, J.E. and K.L. Gray. 1987. Marina State Beach Dune Revegetation. pp. 100-108 In J. Rieger and B. Williams. Second Native Plant Revegetation Symposium. Society for Ecological Restoration. Madison ,Wisconsin.

Kirby, R.H. 1963. Vegetable Fibers. Interscience Publishers, NY pp. 418-419. OWPS (Office of Water Planning and Standards). 1975. Methods of Quickly Vegetating Soils of Low Productivity, Construction Activity. EPA 440/9-75-006. Environmental Protection Agency, Washington, DC. 465 p.

Schiechtl, H. 1980. Bioengineering for Land Reclamation and Conservation. University of Alberta Press, Edmonton, Alberta. 404 p.SCS. 1992. Soil bioengineering for upland slope protection and erosion reduction. Chapter 18. Soil Conservation Service, Engineering Field Handbook. 18:1-50.

Tag El Din, S.S. 1986. Some aspects of sand stabilization in Egypt. In F. El Baz & M.H.A. Hassan, eds. Physics of Desertification. Martinus-Nijhoff, Dordrecht.

Walshe, P. and J. Miller. 1992. French Farmhouses and Cottages. Weidenfeld and Nicolson, London. p. 64.

Wilken, G. C. 1987. Good Farmers: Traditional Resource Management in Mexico and Central America. UC Press, Berkeley, CA pp. 104-5, 150, 161-2.