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Riparian Ecosystem Creation and Restoration:
A Literature Summary

Discussion


The summary of literature on riparian ecosystems obtained from 92 records in the WCR Data Base provided an overview, and relative comparison of the amount, of information available concerning various topics related to creation and restoration of riparian ecosystems (Table 4). Although some aspects of riparian ecosystem creation/restoration were frequently discussed in the literature, information was lacking and is needed for other aspects (Table 4).

As the literature in the WCR Data Base emphasizes, riparian ecosystems generally occupy relatively small areas, and their occurrence along waterways makes them vulnerable to severe alteration caused by a variety of development activities. The status of wetland and riparian ecosystems within the U.S. has been well documented, with estimates of over 50% already destroyed within the coterminous 48 States and few remaining unimpacted. Impacts include expanding agriculture; channelization projects; reservoir and dam construction; heavy livestock grazing (primarily in the West); road, bridge, and pipeline construction; logging activities (particularly in the Northwest); flood control projects; and mining activities (especially in the East).

Riparian ecosystems generally are more structurally diverse and more productive in terms of plant and animal biomass than surrounding areas. Fredrickson and Reid (1986) stress that in the few places where functional natural systems remain, effective and responsive management requires protection of the habitat rather than manipulation. Action agencies should explore all alternatives prior to destroying valuable riparian habitat (Anderson and Ohmart 1979). Although protecting our wetland resources is imperative, restoration is the only way to make up for past, present, and future losses (Hey 1988).

A number of difficulties are encountered when attempting to restore riparian zones to their original condition: (1) the historical condition of rivers might not be well known; (2) ecological means of returning to a known prior condition are not understood, nor is it certain that this is possible; and (3) presence of man-caused phenomena for long periods of time may genetically alter a species to the extent that restoration may affect it unfavorably (Cairns et al. 1979).

Several records in the WCR Data Base point to the lack of information on riparian ecosystem creation/restoration for specific regions of the U.S., particularly the West. Platts et al. (1987b) stated that research and experience in restoring riverine/riparian ecosystems in the Great Basin and Snake River watersheds are limited. Given the lack of information, they recommended that restoration be approached from a more fundamental level, using undisturbed ecosystems as models and borrowing designs from nature. However, lack of relatively pristine watersheds in this region results in scientists only hypothesizing on the undisturbed condition of riverine/riparian ecosystems. Platts et al. (1987b) suggested that representative ecosystems in relatively unimpaired conditions be protected and used as reference sites for riparian habitat creation/restoration efforts.

Much remains to be learned about the ecology of riparian communities, and unfortunately, little information is available on the natural history of most plant species of these communities (Ohmart et al. 1977). This information is crucial for developing adequate revegetation plans and techniques. Roesser (1988) conducted a literature review to aid in selection of appropriate wetland revegetation techniques to be implemented on the Blue River in central Colorado. Interviews were conducted with a number of individuals representing a wide range of institutions and agencies concerned with wetland reconstruction. Results indicated that a large body of detailed literature was available concerning saltwater marsh, dredge spoil, and freshwater pond/marsh revegetation. However, little information was available concerning riverine wetland reconstruction. No studies were known to exist, at that time, dealing with total wetland reconstruction along high altitude river systems.

The need for development of revegetation techniques has increased in Alaska due to man-caused disturbances, primarily hydroelectric and pipeline projects (Johnson and Specht 1975). Conditions of low temperatures and long winters, largely responsible for the discontinuous permafrost of the subarctic, plus the relatively low rainfall, limit the effectiveness of revegetation techniques developed for temperate regions. Research on the use of native vegetation, response of plants to fertilizers, competition among invading nonnative and native plants, and the effective erosion control ability of plants is needed, particularly for this region.

Probably the most critical aspect of restoration projects (at least from the perspective of developers) is cost (Platts et al. 1987b). Cost of restoring a riparian ecosystem to original condition might be so great as to be considered unrealistic by most members of society, although a return of some of the greatly appreciated amenities might be considered a reasonable financial burden (Cairns et al. 1979). Anderson and Ohmart (1979) stressed that if destruction of a riparian ecosystem is necessary, agencies should be prepared to meet the high cost to replace it in kind and place.

Cost evaluation of riparian ecosystem creation/restoration is complicated by the difficulty in placing monetary values on the resources and by the uncertainties (success/failure) associated with restoration efforts (Platts et al. 1987b). Cost: benefit analyses were generally lacking in the WCR Data Base (Table 4) and are needed to support future funding of riparian ecosystem creation/restoration projects. Inclusion of costs in published works concerning creation/restoration projects and techniques will aid in developing cost:benefit analyses in the future. Sandrik and Crabill (1983) suggested that costs of wetland and riparian ecosystem creation/restoration will most likely diminish as more projects are attempted and more data are collected, which will aid in planning future projects.

Although, the primary function of riparian ecosystem creation or restoration discussed in the WCR Data Base was the provision of fish and wildlife habitat (Table 4), floodplain wetlands are complex, dynamic systems heavily influenced by hydrology. As previous discussions of riparian ecosystem functions and plant life indicate, hydrology, soil properties, and water quality have major impacts on development of the wetland plant community, which thus influences the wildlife and fish populations of the created or restored site. Especially in the West, interrelationships between surface water and groundwater hydrology, hydric soils, and riparian plant communities are poorly understood (Ischinger and Schneller-McDonald 1988). Plant community distribution and tolerances of saturated soil conditions along environmental gradients should be documented, as well as the impact of streamflow depletions on riparian wetland ecosystems.

As land becomes increasingly degraded by man's activities, the impetus to create or restore riparian zones to improve the hydrologic flow, flood control ability, erosion control, and water quality will undoubtedly play a more prominent role in creation/restoration efforts and possibly provide needed cost: benefit ratios, which may promote more riparian ecosystem creation/ restoration efforts.

The WCR Data Base literature contains useful information on planning riparian ecosystem creation/restoration projects, with particular attention to collecting baseline data, determining goals and objectives, and site selection (Table 4). Most information on collection of baseline data concerns measuring vegetation parameters.

To aid in planning creation/restoration projects, research is needed to determine: (1) means of predicting recovery rates, (2) management techniques to enhance the recovery process, and (3) methods for maintenance of restored systems and preventing further damage (Cairns et al. 1979).

The most frequently discussed techniques in the WCR Data Base concern revegetating creation/restoration sites (Table 4). However, information concerning selection of native vegetation and obtaining plants to revegetate sites still is lacking for most areas. Fortunately, efforts are being made to provide a broad genetic base and wide selection of plants adapted to specific areas. For example, the New Mexico Department of Game and Fish, jointly with five Federal agencies, is conducting research on riparian plants in New Mexico to expand the number of native riparian plant species commercially available for use in riparian revegetation programs (Swenson 1988).

Vegetation also is the most commonly monitored parameter in the WCR Data Base (Table 4). Informed decisions on planning creation/restoration projects can only be made with adequate information from past efforts. Adapting sampling and monitoring designs, such as proposed in Platts et al. (1987a), and statistically testing results will provide more detailed information from which to base future efforts. As Erwin (1986) noted, the literature on wetland restoration does contain information on vegetation survival and succession, but little comprehensive information on water quality, biological integrity, or the ecological interrelationships in a functional reclaimed wetland system. This type of information can only be obtained by careful and thorough monitoring of creation/restoration efforts.

Fish and birds have been the most commonly monitored animal groups, with little information available on use of created/restored riparian ecosystems by mammals, reptiles, or amphibians. Richness of riparian vegetation and its close proximity to water are conducive to extensive use by mammals, particularly in arid regions, and should be investigated more during creation/restoration efforts.

Much of the information on nongame wildlife associated with wetland and riparian ecosystems has accumulated because of specific research interests in a species or a taxonomic group, or to test hypotheses relating to ecological questions (Fredrickson and Reid 1986). Such published information on nongame species often has high value for management, but the syntheses needed by land managers generally are lacking. Another important deficiency for wetland managers and administrators is the lack of information that identifies wetland management values for nongame wildlife that are not obligate wetland species. For example, bats and swallows feed on insects emerging from wetlands, captors prey on wetland wildlife, and many seed-eating songbirds forage in wetlands. These vertebrates are not traditionally recognized as wetland species, yet wetlands play an important role in providing nutritional needs in their annual cycle.

Results of creation/restoration efforts frequently include only 1-2 years of data. Anderson and Ohmart (1982) stated that 2 years of data from their study of riparian ecosystem creation/restoration along the lower Colorado River was not enough time from which to draw any conclusions beyond that time or beyond the range of variables studied. They cautioned against using findings from their report for making predictions about plant growth and mortality after 4-10 years and stated that the report should be considered preliminary until the site was at least 15-20 years old. Documentation of creation/restoration efforts over extended periods is needed to project changes over time, improve the success rate of future projects, and provide scientific evidence of the success or failure of restoring riparian ecosystem functions.

Reasons for restoring wetlands must be clearly articulated, and success must be demonstrated to ensure future funding of endeavors (Hey 1988). Clearly, success of a particular project cannot be properly evaluated without detailed baseline data, careful and thorough monitoring, and an analysis of the data obtained over a long period of time. The three case studies discussed in the previous section exemplify efforts to achieve some of these goals. Success determinations would benefit from an investigation of various functions of riparian wetlands (including wildlife and fish habitat, hydrologic flow, erosion control, water quality improvement, and recreational use).

An important aspect of riparian ecosystem creation/restoration efforts is the documentation of monitoring results and making the information available to agencies and scientists (Platts et al. 1987b). Miller (1988) recommended that monitoring each site with standardized tests and setting expectation levels that indicate success be a standardized part of the permitting process. She also recommended that Federal, State, and local agencies set the same criteria.

In publishing results of riparian ecosystem creation/restoration efforts, consistent use of a wetland classification system, such as Cowardin et al. (1979), would aid in project comparisons, along with detailed descriptions of the project sites. Ischinger and Schneller-McDonald (1988) recommended that riparian ecologists adopt nationally accepted definitions of hydric soils and wetland plants to facilitate classification systems consistent with nationally recognized or statutory definitions.

In conclusion, the literature on riparian ecosystem creation/restoration in the WCR Data Base appears to stress three major needs: (1) protecting remaining natural, undegraded riparian ecosystems; (2) describing, creating/restoring, and monitoring riparian functions; and (3) increasing the emphasis on documenting creation/restoration efforts and publishing this information. The knowledge base of riparian ecosystem creation/restoration efforts needs to be increased if decision makers, planners, and managers are to have the necessary data to make informed decisions concerning protecting existing riparian ecosystems and to use creation or restoration to compensate for unavoidable loss of this valuable resource.


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