Riparian Areas: Functions and Strategies for Management


by Laura Ehlers and Ellen de Guzman


The federal Clean Water Act requires that wetlands be protected from degradation because of their multiple, important ecological roles including maintenance of high water quality and provision of habitat for fish and wildlife. For the last 15 years, this protection has slowed the precipitous decline in wetland acreage observed in the United States since European settlement. However, protection of wetlands generally does not encompass riparian areas — the lands bordering water bodies such as rivers, lakes, and estuaries — even though they often provide many of the same functions as wetlands. Especially in more arid regions of the country, riparian areas support the vast majority of wildlife species, and are the predominant sites of woody vegetation including trees. They also surround what are often the only available surface water supplies. Growing recognition of the similarities in functioning of wetlands and riparian areas and the differences in their legal protection led the National Research Council in 1999 to undertake a comprehensive study of riparian areas, which has culminated in a new report Riparian Areas: Functioning and Strategies for Management.

Several overarching conclusions and recommendations intended to heighten awareness of riparian areas commensurate with their ecological and societal values. First, restoration of riparian functions along America’s water bodies should be a national goal. Over the last several decades, federal and state programs have increasingly focused on the need for maintaining or improving water quality, ensuring the sustainability of fish and wildlife species, protecting wetlands, and reducing the impacts of flood events. Because riparian areas perform a disproportionate number of biological and physical functions on a unit area basis, their restoration can have a major influence on achieving the goals of the Clean Water Act, the Endangered Species Act, and flood damage control programs.


Zone of Influence

Second, protection should be the goal for riparian areas in the best ecological condition, while restoration is needed for degraded riparian areas. Management of riparian areas should give first priority to protecting those areas in natural or nearly natural condition from future alterations. The restoration of altered or degraded areas could then be prioritized in terms of their relative potential value for providing environmental services and/or the cost-effectiveness and likelihood that restoration efforts would succeed. Where degradation has occurred — as it has in many riparian areas through-out the United States — there are vast opportunities for restoring functioning to these areas.

Third, patience and persistence in riparian management is needed. The current degraded status of many riparian areas throughout the country represents the cumulative, long-term effects of numerous, persistent, and often incremental impacts from a wide variety of land uses and human alterations. Substantial time (years to decades) will be required for improving and restoring the functions of many degraded riparian areas. Commensurate with restoration must be efforts to improve society’s understanding of what riparian functions have been lost and what can be recovered.

Finally, although many riparian areas can be restored and managed to provide many of their natural functions, they are not immune to the effects of poor management in adjacent uplands. Upslope management can significantly alter the magnitude and timing of overland flow, the production of sediment, and the quality of water arriving at a downslope riparian area, thereby influencing the capability of riparian areas to fully function. Therefore, upslope practices contributing to riparian degradation must be addressed if riparian areas are to be improved. In other words, riparian area management must be a component of good watershed management. Definition, Structure, and Functioning Because the lack of a single concise ecological definition of “riparian” has been identified as a major problem of federal and state programs that might manage and protect these areas, the report contains the following definition:

Riparian areas are transitional between terrestrial and aquatic ecosystems and are distinguished by gradients in biophysical conditions, ecological processes, and biota. They are areas through which surface and subsurface hydrology connect water-bodies with their adjacent uplands. They include those portions of terrestrial ecosystems that significantly influence exchanges of energy and matter with aquatic ecosystems (i.e., a zone of influence). Riparian areas are adjacent to perennial, intermittent, and ephemeral streams, lakes, and estuarine-marine shorelines.

Figure 1 is a conceptual diagram of riparian areas. Riparian areas encompass complex above- and below-ground habitats created by the convergence of biophysical processes in the transition zone between aquatic and terrestrial ecosystems. Even though they occupy only a small proportion of the total land base in most watersheds, riparian areas are regional hot spots of biodiversity and exhibit high rates of biological productivity in marked contrast to the larger landscape. This is particularly dramatic in arid regions, as evidenced by the high number of plant and animal species found along watercourses and washes. Although riparian areas encompass some of the wetlands in a typical landscape setting and also include portions of adjacent aquatic and upland environments, important distinctions between these systems are made in the report. Human Alterations of Riparian Areas Because humans worldwide use more than half of the geographically accessible river runoff, their significant impact on the structure and functioning of riparian areas is not surprising. Drastic declines in the acreage and condition of riparian lands in the United States over the last 100 years are testimony to these effects. Effects include changes in the hydrology of rivers and riparian areas, alteration of geomorphic structure, and the removal of riparian vegetation. The report comprehensively discusses the impacts to riparian areas from agriculture, industrial activities, urban development, and recreation.

Although the available data are highly variable, it is clear that riparian areas are some of the most severely altered landscapes in the country. The majority of riparian areas in the United States have been converted or degraded. The spatial extent of riparian forests has been substantially reduced, plant communities on floodplains have been converted to other land uses or replaced with developments, and the area of both woody and non-woody riparian communities has decreased. The functions of these riparian areas are greatly diminished in comparison to what occurred historically. Existing Legal Strategies for Riparian Area Protection Only during the last decade have riparian areas begun to receive legal recognition as places requiring special attention. Five approaches have been used to protect riparian areas, depending on whether the land is publicly or privately owned. These include federal laws that require the evaluation of adverse effects that would be caused by federal actions; placing special limits on activities in riparian areas on public lands; regulating activities in privately owned riparian areas; using incentives such as cost-sharing, low-cost loans, or tax reductions to encourage stewardship on private riparian areas; and purchasing privately owned riparian lands (either in fee or by easement) for public management.

The report recommends that public lands be managed to protect and restore functioning riparian areas through the promulgation of regulations requiring that the values and services of riparian areas (habitat-related, hydrologic, water quality, aesthetic, recreational) be restored and protected. It explores opportunities for protection of riparian areas by extending water rights to instream uses. Management of Riparian Areas The range of possible restoration activities in riparian areas is broad, spanning from simple activities at a single site to large-scale projects. In many cases, relatively easy things can be done to improve the condition of riparian areas, such as planting vegetation, removing small flood-control structures, or reducing or removing a stressor such as grazing or forestry. Where the objective of restoration is to improve the entire river system, more holistic watershed approaches will be necessary, and management strategies such as removing impediments to the natural hydrologic regime may be required.

Perhaps the most important restoration need is to reestablish or restore these disturbance regimes to the extent possible. This may involve modifying dam operations where possible, which will help restore downstream riparian areas.

Where riparian vegetation has been degraded or removed, its recovery is a necessary part of any restoration effort. Both passive (e.g., exclusion from forestry or grazing) and active (e.g., planting trees) approaches are possible, depending on the goal of the restoration effort.

The report concludes that riparian areas provide essential life functions such as maintaining streamflows, cycling nutrients, filtering pollutants, trapping and redistributing sediments, absorbing and detaining floodwaters, maintaining fish and wildlife habitats, and supporting the food web for a wide range of biota. The future success of at least five national policy objectives — protection of water quality, protection of wetlands, protection of threatened and endangered species, reduction of flood damage, and beneficial management of federal public lands — depends on the restoration of riparian areas.

The study was sponsored by the U.S. Department of the Interior Bureau of Land Management, Bureau of Reclamation, and Geological Survey, by the National Science Foundation, by the U.S. Department of Agriculture Natural Resource Conservation Service and Forest Service, and by the U.S. Environmental Protection Agency. It was chaired by Mark Brinson of East Carolina University. Copies of the report are available through the National Academy Press             (800) 624-6242       or Laura Ehlers is a Senior Staff Officer with the WSTB and Ellen de Guzman is a Research Associate with the WSTB.