Riparian Ecosystem Creation and Restoration:
A Literature Summary
Techniques
Fencing
Fencing created or restored riparian zones from livestock grazing is used particularly in the western U.S. (Table 2). Livestock grazing can have detrimental effects on riparian vegetation. Areas with heavy livestock use also have increased total and fecal coliforms in waters compared to ungrazed or lightly grazed areas, decreased invertebrate diversity, and decreased use by spawning fish due to increased silt-sediments (Duff 1979).
Duff (1979) stresses the need to consider riparian-aquatic habitats as separate pastures from uplands within grazing management allotments of the Bureau of Land Management to ensure protection of this sensitive habitat from overgrazing. A minimum of 8 years of exclosure of riparian vegetation on Big Creek, Rich County, Utah, was necessary to restore the habitat for productive fish and wildlife uses, as well as water-quality maintenance (Duff 1979). After 10 years of livestock exclusion, Rattlesnake Springs, a small permanent spring/stream in south-central Washington, supported a nearly continuous narrow corridor compared to the extremely sparse amount of riparian trees and shrubs present before fencing (Rickard and Cushing 1982).
Experimental habitat treatments on three segments of Texas Creek in Colorado consisted of: (1) deferred seasonal livestock grazing with no habitat treatment; (2) fencing to exclude livestock with intensive habitat treatment of gabion drop structures, planting willows, resloping, and placing riprap along a portion of the streambank; and (3) fencing with no habitat treatment (Prichard and Upham 1986). The best improvement in habitat quality occurred on the area fenced and under intensive habitat treatment. Gabions instantly improved the pool/riffle ratio, began to develop well-defined reads at the tail of each pool, and greatly enhanced the recovery of vegetation by subirrigation. In 3 years, banks were stabilized; undercuts were well developed in 5 years. In 6 years, heavy bank cover of medium to tall trees and shrubs developed, augmented by willow plantings and streambank stabilization. All three areas showed an increase in brown trout (Salmo trutta), with the second treatment showing the widest range in trout size, relating directly to habitat treatments. In this case, removing livestock alone did not greatly improve the riparian habitat over the 6 years of the study.
Fifteenmile Creek, a small Columbia River tributary in north-central Oregon, had been seriously degraded due to increased crop production, livestock grazing, fires, herbicides, and rechanneling by landowners attempting to reduce field erosion and produce more regularly shaped fields to ease cultivation and irrigation (Newton 1984). Severe flooding problems prompted the Wasco County Soil and Water Conservation District to develop methods to prevent future floodings. Corrective practices included sloping vertical cut banks, seeding banks with grass, armoring vulnerable sites with riprap, constructing rock check dams to reduce stream velocity, and fencing the stream corridor to exclude livestock and encourage revegetation. The level of stream corridor recovery was dramatic, but on areas of continual livestock grazing, vegetative cover was severely retarded or nonexistent. Thus, fencing was necessary through agricultural areas for recovery of the riparian vegetation along this severely degraded stream. In areas of livestock enclosures, continuous bands of young trees formed within 5 years, and grasses, sedges, and rushes effectively armored previously erodible banks.
In southwestern Wyoming, the use of fencing was supplemented by the introduction of beavers to encourage the development of willow and other riparian plants in an expanded riparian zone (Apple et al. 1984). The technique appears to be successful in stabilizing streambanks and improving riparian and aquatic habitat in cold desert, gully-cut stream systems of this region.
Livestock grazing in riparian habitats can result in heavy siltation of streams, making them unsuitable for fish spawning. In addition to fencing the area to prevent further grazing pressure, other habitat improvement methods directed toward improving the fisheries may be necessary. Due to poor streambed conditions on Bone Draw, an ephemeral tributary of the Big Sandy River in Wyoming, artificial redds were placed in the streambed to create suitable habitat for establishment of a seasonal anadromous trout run and the stream was stocked with trout (Smith and Dunder 1984). Siltation was still a problem after initial placement of gravel for the reads, but should improve as the riparian habitat recovers from grazing pressure.
Stock water access, stream crossings, and impacts of flooding need to be considered in fencing designs on private land. Reichard (1984) presents some designs for livestock barriers, stream crossings, and water access points. She also presents designs for various bank stabilizing methods to create stable ground for the growth of planted or volunteer riparian vegetation: willow mattresses, brush and tree deflectors, and double fence revetment. Planting vegetation on protected streamside land may significantly accelerate riparian thicket recovery. In some situations, competition from pasture plants and moisture stress can be the primary limiting factors for rate of riparian reestablishment. Irrigation and suppression of competing pasture plants may be necessary for native plant establishment.
Previous Section -- Planting
Return to Contents
Next Section -- Landforming
