Northern Prairie Wildlife Research Center
Nelson et al. (1978) developed a guide for selecting effective habitat improvements for streams and reservoirs. Measures recommended by the FWS are identified, and the effectiveness of these measures is critically evaluated. The guide includes discussions of dam discharge, stream flow, instream devices, artificial meanders, bank cover, bank stabilization, food and cover plantings, grazing control, zoning, and a variety of fish and wildlife habitat improvement measures (e.g., nesting structures, fishways, wildlife crossings). The main emphasis of the guide is not riparian ecosystems; however, some techniques are useful for riparian ecosystem creation or restoration.
Platts et al. (1987a) present a summary of techniques that have been used to prepare, seed, plant, and protect riparian revegetation sites. McCluskey et al. (1983) present a guide to planting willow cuttings. For many areas, cuttings of willows are easier to obtain and cheaper than transplants and can be taken from local sources better adapted to specific site conditions. A short discussion of evaluating a stream for need and suitability for willow plantings and maintaining the project site also is included.
The North Carolina Wildlife Resources Commission (1979) has set standard guidelines for stream relocations in the State to facilitate road project reviews by the Commission and to assist engineers in designing projects. Topics include matching original channel length, slope, meander pattern, depth, and width; sloping banks; stabilizing banks with riprap and vegetation; planting trees and shrubs; fencing; using suitable substrates; installing culverts and stream crossings; and using instream structures (boulders, low rock and stone dams, deflectors) to enhance habitats of low-, medium-, and high-gradient streams
The American Fisheries Society--Western Division (1982) presents best management practices for Western streams, including tailing pond construction in mined areas (used to settle out finely ground rock and prevent accidental release of toxic materials to the aquatic ecosystem), mine pond reclamation, enhancing channelized streams, stream relocation, revegetation techniques, and restoration of riparian ecosystems.
Consideration of natural succession on man-made habitats is important in any creation effort. Unfortunately, few studies have examined natural succession on created riparian ecosystems. An investigation of plant succession on dredge spoils (consisting of unsorted boulders and cobbles with intervening swales of fine-textured soils and standing water) on the Merced River in central California revealed that vegetation is generally not diverse due to slow weathering of spoil and lack of soil moisture (Whitlow and Bahre 1984). Only in a few swales with moist, shallow soils and standing water was vegetation diverse or structurally complex. Results indicated that 50 years or more were required for the accumulation of well-developed flora. Structural changes are expected to be even slower, correlating with slow soil development.
A study of vegetation succession in relation to age of river stabilization structure along the Missouri River floodplain from Sioux City, Iowa, to Rulo, Nebraska, revealed that early herbaceous vegetation had little or no significance in the future course of succession (Vaubel and Hoffman 1975). Initial stages of succession began with willow and cottonwood (Populus deltoides); shrub species did not appear until 18 years later. Few relationships were found between soil characteristics and plant communities, probably as a result of immature soils exhibiting parent material characteristics. However, soils tended to have a higher clay content and greater amounts of nitrogen and organic matter in mature floodplain communities dominated by oaks (Quercus spp.), basswoods (Tilia spp.), and hickories (Carya spp.). Relating vegetation succession to age of river structure was found to be a precise method of developing a time-scale of vegetation development, which could be valuable in managing riparian habitats along these structures.
Although some channelized streams revegetate by natural succession, the extent and rate at which reestablishment occurs is unpredictable and depends on a number of little-understood variables (Goldner 1984). These variables include channel slope lining (concrete or riprap), availability of upstream seed sources, soil temperature and moisture, streamflow regime and velocities, steepness of side slopes, fertility and compactness of fill material, and intensity of vegetation and sediment removal in the channel to maintain the constructed flow capacity.
Removal of competing vegetation can result in a substantial increase in emergence and growth rates of new willow shoots (Harrington 1986). New stems appear to be suppressed by existing stems. Survival of new stems also is affected by water table fluctuations. Constant water table level throughout the growing season resulted in the greatest spreading rates of clonal sandbar willow (Salix interior) in Wisconsin.
Various smaller-scale case studies and laboratory or field experiments demonstrate the usefulness of some techniques used to create or restore riparian habitats (Table 2) and are included in the discussion below under the main technique used in the creation/restoration effort. Examples of more extensive case studies, well documented in the literature, are discussed in the Case Studies section.