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Riparian Areas Reservoirs of Diversity

Working Paper No. 13

Gerald L. Montgomery
Northern Plains Regional Office
Lincoln, Nebraska

February 1996




Riparian areas are the zones along water bodies that serve as interfaces between terrestrial and aquatic ecosystems. Riparian ecosystems generally compose a minor proportion of the landscape. Typically, however, they are more structurally diverse and more productive in plant and animal biomass than adjacent upland areas. Riparian areas supply food, cover, and water for a large diversity of animals, and serve as migration routes and connectors between habitats for a variety of wildlife (Manci 1989).

Riparian areas are important in mitigating or controlling nonpoint source pollution. Riparian vegetation can be effective in removing excess nutrients and sediment from surface runoff and shallow ground water and in shading streams to optimize light and temperature conditions for aquatic plants and animals. Riparian vegetation, especially trees, is also effective in stabilizing streambanks and slowing flood flows, resulting in reduced downstream flood peaks.

Riparian areas are often important for their recreation and scenic values, such as hunting, fishing, boating, swimming, hiking, camping, picnicking and birdwatching. However, because riparian areas often are relatively small areas and occur in conjunction with watercourses, they are vulnerable to severe alteration.

Riparian ecosystems throughout the United States have been heavily impacted by human activities, such as highway, bridge, and pipeline construction; water development; channel modifications for flood control; recreation; industrial and residential development; agriculture; irrigation; livestock grazing; logging; and mining. Offsite disturbances in the watershed that change watershed hydrology can also have adverse effects on the composition and productivity of riparian plants and corresponding animal associations (Manci 1989).

Nature and Significance

According to the Oxford English Dictionary, the term "riparian" is derived from the Latin word ripa, meaning river bank. In recent years, there have been numerous attempts to refine this definition by including specific criteria on such features as soil moisture and vegetation. The term has been expanded by many to include areas along all water bodies, including lakes, ponds and some wetlands. There are now several definitions for riparian areas, but all of them have much in common. Riparian areas are zones that influence and are strongly influenced by an adjacent aquatic environment.

The Natural Resources Conservation Service (NRCS) defines riparian areas in its General Manual as "ecosystems that occur along watercourses and water bodies. They are distinctly different from the surrounding lands because of unique soil and vegetation characteristics that are strongly influenced by free or unbound water in the soil. Riparian ecosystems occupy the transitional area between the terrestrial and aquatic ecosystems. Typical examples would include floodplains, streambanks, and lakeshores" (190-GM, Part 411).

NRCS indicators of riparian areas include:

  • Vegetation--The kinds and amounts of vegetation will reflect the influence of free or unbound water from an associated watercourse or water body and contrast with terrestrial vegetation.
  • Soils--Soils in natural riparian areas consist of stratified sediments of varying textures that are subject to intermittent flooding or fluctuating water tables that may reach the surface. The duration of the soil-wetness feature is dependent upon the seasonal meteorological characteristics of the adjacent water body.
  • Water--Riparian areas are directly influenced by water from a watercourse or water body. Riparian areas occur along natural watercourses, such as perennial or intermittent streams and rivers, or adjacent to natural lakes. They may also occur along constructed watercourses or water bodies such as ditches, canals, ponds, and reservoirs (190-GM, Part 411).

Topography, relief, climate, flooding, and soil deposition most strongly influence the extent of water regimes and associated riparian zones. Likewise, the riparian area exerts considerable control on the flows in the landscape, especially on the movement of water, nutrients, sediments, and animal and plant species. Thus the appearance and boundary of a riparian area vary from site to site. Riparian areas occur as complete ecosystems or as ecotones (transition zones) between aquatic and terrestrial ecosystems. They may also occur as more gradual transition zones, called ecoclines.

Some riparian areas meet the criteria established for wetlands (Cowardin et al. 1979). Others do not, because they do not possess the necessary hydrologic water regime, a predominance of hydric soils, or a prevalence of hydrophytic vegetation. Even nonwetland riparian areas, however, share many characteristics, functions, and values with wetlands.

In addition to the vertical transition between aquatic and terrestrial ecosystems, riparian areas possess a distinct longitudinal structure. Drainage patterns form an extensive, dendritic network throughout the country. The associated riparian zones form corridors that extend within and into different regions. There will also be variation along riparian areas because of changing forces in the watershed from the headwaters to the mouth of the river. The general spatial pattern of riparian areas thus forms a longitudinal gradient of height and width and becomes a network within an overall matrix (Malanson 1993).

Regional Differences

Because of the vast differences in climate, topography, and other features, riparian areas take on different appearances in different regions of the country. In humid areas, riparian landscapes are somewhat indistinct, while in dry areas, the river itself contrasts strongly with the surroundings, the gradient of moisture away from the river is sharp, and boundaries are clear.

In arid regions, riparian vegetation is usually more productive than the adjacent land, so the vegetation stands much taller than the vegetation in the surrounding landscape. The riparian zone is relatively narrow and is generally visually distinct. An example is a stream, lined with willows or cottonwood trees, that flows through native grassland.

While all riparian areas tend to be linear, those along alluvial floodplains in the southern humid regions are relatively wide. Because the riparian element is not so distinct, its interactions with surrounding elements are more difficult to discern. An example is a broad floodplain of mixed bottomland hardwood trees with intermingled baldcypress swamps adjacent to a forest of upland hardwood trees. Extensive deforestation and resulting conversion of much of the riparian area to cropland or other land uses provide examples where the landscape pattern becomes more apparent.

Farther upstream in the humid temperate forest the riparian zone does not markedly alter the visual landscape. Nevertheless, these zones are ecologically distinct.

Riparian areas in western mountain regions are quite variable. They may be very narrow forests along downcutting streams in mountain valleys. On the other hand, the ecological distinction may appear only among the understory species, as the dominant trees may be those generally found also on mesic sites and not specifically on riparian sites.

In the subarctic, the overall species diversity is less than that at low latitudes, but it is at its greatest on riparian areas.

Functions and Values

Riparian areas function in different ways and display different values because of their variation across the country. In spite of their differences, riparian areas possess some basic ecological characteristics such as energy flow, nutrient cycling, and community structure. These characteristics often function in particular ways that give riparian areas unique values. Below are some of the more recognizable functions and values of riparian areas.

The importance of riparian areas is mostly attributed to their spatial relationship in the landscape. Few other ecosystem types possess such a large amount of transition zone relative to the area that they occupy. These transition zones are the points at which terrestrial and aquatic ecosystems interface and the sites of important exchanges of material and energy in the landscape (Brinson et al. 1981).

Fluvial Processes

Natural fluvial processes are responsible for many of the diverse, often subtle, topographic features on floodplains and consequently responsible for forming riparian ecosystems. These processes (Leopold et al. 1964) are driven by flooding events. Basically, they result from a combination of the deposition of alluvial materials (aggradation) and downcutting of material (degradation) over many years. Floodplain features do not necessarily remain static; in fact, morphological features of floodplains continually change.

As river channels meander laterally and in a downstream direction, material is removed from the outside curve of a meander, resulting in erosion of the riparian area. The eroded sediment, however, is deposited on the inside curve farther downstream, forming point bars. Eventually, the point bar begins to support vegetation and develops into a stable riparian area.

Once flood waters overtop the streambanks, they lose much of their velocity and their ability to carry sediment. Flood-borne sediments are then deposited in the floodplain. The coarser, heavier material drops out first, forming natural levees adjacent to the channel. Finer material is deposited in the floodplain further away from the channel. Severe flooding may scour areas in the floodplain and redeposit the sediment elsewhere, resulting in increased undulation of the floodplain.

These fluvial processes are important to riparian ecosystems because they create a diverse set of conditions in a seemingly level floodplain. The small topographic variations can mean the difference between a waterlogged, anaerobic environment and a well-drained, aerated substrate. Many plant species are intolerant of even brief periods of inundation, while few species are adapted to survive in constantly waterlogged soil. In addition to the variation in soil moisture, major differences may occur in soil texture and fertility. Coarser, less fertile soils will be found in certain areas and finer, more fertile soils in other areas. As a result, abrupt changes in species composition may occur in floodplains with elevational variations of only a few centimeters (Brinson et al. 1981).


The flooding that shaped the floodplain is also important to riparian ecosystems because it can affect the metabolism and growth of vegetation in three basic ways. First is water supply, whereby water storage is recharged through seepage and channel overflow to floodplains. Secondly, nutrient supply in riparian ecosystems depends partly on sedimentation of particulate matter transported by overbank flow and partly on the availability of dissolved nutrients in the water in contact with floodplain soils. Finally, flowing water in floodplains ventilates soils and roots so that gases are exchanged more rapidly. Oxygen is supplied to roots and soil microbes, while the release of gaseous products of metabolism such as carbon dioxide and methane is enhanced. Water flow then provides the medium for the export of these dissolved organic compounds (Brinson et al. 1981).

The hydroperiod of the riparian ecosystem, which includes its flooding duration, intensity, and timing, is the ultimate determinant of the ecosystem structure and function. The timing of flooding is particularly important because flooding in the growing season has a greater effect on ecosystem productivity than does an equal amount of flooding in the nongrowing season (Mitsch and Grosselink 1986).

Ground water in the alluvial aquifer has an intimate relationship with surface water in streams and floodplain depressions (e.g., oxbow lakes). The normal gradient and direction of ground water movement is toward these surface water features through ground water discharge. During periods of high river stages, the gradient is reversed and water moves from the stream to the aquifer.

Base Flows

Alluvial soils in riparian areas are usually deep and store large quantities of water, from rainfall and from water moving downslope. Many alluvial aquifers in the western United States are maintained by infiltration of upland runoff in the stream channel or riparian alluvial deposits. Water storage in such aquifers is partly responsible for maintaining base flow in many rivers (Lowrance et al. 1985). Base flows are further maintained by riparian vegetation that shades the water, keeping it cooler and thus reducing rapid evaporation.

Nutrient Cycling

Dissolved nutrients and those attached to sediment are transported from terrestrial ecosystems into streams during runoff events and carried downstream where they come in contact with the soils of riparian areas. Other nutrients moving toward a stream, either in ground water or surface runoff, may be intercepted by riparian areas before they reach the stream. Once these nutrients enter a riparian area, they are exposed to mechanisms that may utilize or alter them in different ways.

Nutrients, especially nitrogen, phosphorus, calcium, magnesium, and potassium dissolved in overflow water and those attached to deposited sediments, are taken up by shallow-rooted riparian vegetation. Dissolved nutrients moving with the ground water and those that are leached in the soil may be intercepted by deeper-rooted riparian vegetation. Local cycling of nutrients occurs with the uptake of transported nutrients by root systems, to be temporarily stored in the leaves and then returned to the soil surface when the leaves (or needles) are shed. Long-term accumulation of some nutrients occurs in the boles and branches of trees and shrubs.

Not all nutrients remain in the riparian area, and the release processes are seasonal. Some nutrients pass through with no significant detention. Some that were taken up by riparian vegetation may be reintroduced into the water column when the vegetation dies. This form of release produces nutrients that are highly soluble.

Vegetation supplies litter that, when covered with sediment during overflow, rapidly decomposes to release nutrients and adds humus to the soil. This adds to the complex mosaic of sands, silts, and clays deposited by flowing water. These seasonally waterlogged soils and subsoils that are rich in organic matter provide ideal conditions for production of microbial organisms that are important in the transformation of nitrogen.

A thin oxidized layer at the soil-water interface results from the diffusion of oxygen from water or the atmosphere into the soil. This aerobic layer is a small refuge of aerobic bacteria that are responsible for conversion of ammonium N to nitrate (nitrification). This form of nitrogen is soluble and subject to leaching to the anaerobic layer, where anaerobic bacteria convert the nitrate-nitrogen to gaseous forms (denitrification) that eventually escape to the atmosphere.

Energy Transfer

Riparian areas are unique ecosystems in the manner in which some of the energy as organic matter or organic carbon is transferred from producer to consumer organisms. This uniqueness derives from the fact that litter-fall produced within the riparian ecosystem may be transported laterally and made available to instream animal communities as well as those downstream from the source of organic matter production. As compared with purely aquatic or terrestrial ecosystems, organic matter produced in riparian ecosystems has the potential of supporting a diversity of food webs within both habitat types.

Streams in the upper reaches of a watershed that have negligible or narrow floodplains receive organic matter from the riparian zone principally as litter falling directly from streamside vegetation to the surface of the stream. Flood events may transport litter from the streambanks into the channel and on downstream. In comparison, not only do streams farther down in the watershed (and thus having a higher proportion of floodplain to upland surface area) receive the litter falling directly into their channels, but the inundation of broad floodplains provides the opportunity for transport of additional organic matter from the floodplain (Brinson et al. 1981).

Downstream Flooding

Riparian areas serve an important function in reducing downstream flood peaks by reducing floodwater velocities. As floodwater flows through a vegetated area, the plants act as resisters to the flow and dissipate the energy. Riparian areas are important in this regard, because these areas support much vegetation during periods of expected flood flows.

Not all plants are equal in their effectiveness in slowing floodwater. Low-growing plants are usually quite dense and provide excellent resistance. However, once the floodwater rises to a height that submerges these plants, very little reduction in velocity is then achieved. Trees, on the other hand, may not grow quite as dense, but they continue to provide resistance during severe floods.

Water Quality

As previously mentioned, as floodwaters spread over a floodplain, water velocities are reduced, allowing much of the sediment to settle out with little likelihood of its reentering the stream. Additional sediment carried by overland flow from adjacent uplands is intercepted by the riparian area, where it settles out. Riparian vegetation further increases sedimentation in the floodplain by filtering additional sediment from runoff and floodwaters. The result is that riparian areas serve as effective sediment traps and reduce the amount of sediment that might otherwise get to a stream or downstream water body.

Riparian vegetation also plays an important role in reducing sediments in water by decreasing the rate of bank erosion. This is especially true of deep-rooted woody vegetation. Vegetation protects a streambank from erosion by reducing the tractive force of water, by protecting the bank from direct impacts, and by inducing deposition (Parsons 1963).

Nutrients, pesticides, and heavy metals that are transported with sediment are also trapped in the riparian area. Many of these are broken down by physical or biochemical processes and reduced to harmless forms. Some are taken up by riparian vegetation and incorporated into their living tissues during the growing season. Others are bound to the sediments and permanently stored in the soils of the riparian area.

Most sediment and nutrient studies associated with riparian areas have been conducted in southeastern floodplain forests, where the presence of relatively long hydroperiods and broad floodplains has considerable influence on water quality of streams and rivers. Results vary somewhat, but most indicate a considerable reduction in sediment and nutrients, especially nitrogen and phosphorus transported downstream in comparison with the amount that entered the riparian area.

Riparian vegetation also can have a great impact on water temperatures. Reduced stream temperature can increase a stream's oxygen-carrying capacity and reduce nutrient availability. This is particularly important during the hot summer months.

Solar radiation is selectively absorbed and reflected as it passes through the riparian canopy. The degree of shading of streams is a function of the structure and composition of riparian vegetation. Dense, low, overhanging canopies greatly reduce light intensity at the water's surface, but high, relatively open canopies allow greater amounts of light to reach the stream. Deciduous riparian vegetation shades streams during summer, but modifies light conditions only slightly after leaf fall, whereas evergreen riparian zones shade stream channels continuously. As channel width increases, the canopy opening over the stream increases and the influence of streamside vegetation on solar inputs to the stream channel decreases (Gregory et al. 1991).

Aquatic Life

Riparian vegetation is important to aquatic ecosystems because it regulates the energy base by shading and supplying plant detritus to the stream. Shading affects both stream temperature and light available to drive primary production. In shaded streams, detritus becomes the basis of a food chain that results in a unique and diverse community (Cummins 1974).

Narrow headwater streams are influenced most by riparian vegetation, both through shading and as the source of organic matter inputs. These low-light, high-gradient, constant-temperature streams receive an abundant supply of coarse particulate matter in the form of plant detritus. A group of macroinvertebrates known as shredders reduce detrital material to smaller particulate organic matter which becomes the food for another group of invertebrates, collectors. The abundance of life further supports both macroinvertebrate and fish predators (Vannote et al. 1980).

As the stream widens and more light penetrates the water, algae replace detritus as the primary food source. Here collectors become more abundant in the community, along with grazers, invertebrates that feed directly on the algae. Invertebrate and fish species that are more tolerant of warmer conditions replace species that depend on the cooler, shaded stream. The abundance of individuals within a species may increase, but species diversity usually decreases as the stream becomes less influenced by the riparian vegetation (Vannote et al. 1980).

Rooting herbaceous and woody vegetation also helps shape aquatic habitat by stabilizing streambanks, retarding erosion, and, in places, creating overhanging banks which serve as cover for fish. Above ground, woody riparian vegetation is an obstruction to highwater streamflow and to sediment and detritus movement and is a source of large organic debris. Large organic debris in streams controls the routing of sediment and water through the system; defines habitat opportunities by shaping pools, riffles, and depositional sites and by offering cover; and serves as a substrate for biological activity by microbial and invertebrate organisms (Meehan et al. 1977).

Terrestrial Life

Undisturbed riparian ecosystems normally provide abundant food, cover, and water. Often they contain some special ecological features or combinations of features that are not found in upland areas. Consequently, riparian ecosystems are extremely productive and have diverse habitat values for wildlife (Brinson et al. 1981).

The most visible evidence of the importance of riparian areas for wildlife has been demonstrated in the western United States. Even though riparian habitat comprises less than one percent of the total land area in the western United States, these areas support a tremendous number and diversity of terrestrial wildlife. In parts of southeastern Oregon and southeastern Wyoming, more than 75 percent of terrestrial wildlife species are dependent upon riparian area for at least a portion of their life cycle. In Arizona and New Mexico, at least 80 percent of all animals use riparian areas at some stage of their lives, and more than half of these species are considered to be riparian obligates (Chaney et al. 1990).

Studies in the southwestern United States show that riparian areas support a higher breeding diversity of birds than all other western habitats combined (Anderson and Ohmart 1977, Johnson et al. 1977, Johnson and Haight 1985). Western riparian habitats also harbor the highest noncolonial avian breeding densities in North America (Johnson et al. 1977). Stevens et al. (1977) reported riparian plots to contain over ten times as many migrant passerine species as adjacent nonriparian plots. They also found at least twice as many breeding individuals and species in riparian zones as in nonriparian zones. Additionally, over 60 percent of the species which are identified as neotropical migratory birds use riparian areas in the West as stopover areas during migration or for breeding habitat (Krueper 1993).

Riparian areas have also been shown to be important to wildlife throughout the rest of the country as well. Along the Rio Grande in west Texas, several avian species are present that are absent or rare elsewhere, and numerous species utilize the river corridor as routes through inhospitable habitat (Hauer, 1977). Tubbs (1980) reported that 73 percent of birds which have bred in the Great Plains are associated with riparian areas. In the southeastern United States, studies have shown that floodplain forests support more birds than upland pine stands (Dickson 1978).

Brinson et al. (1981) summarized some of the key factors making riparian areas valuable for wildlife habitat. They include woody plant communities, surface water and soil moisture, spatial heterogeneity of habitats (edges/ecotones), and corridors (migration and dispersal routes).

Woody riparian communities offer a variety of wildlife habitat values and may be critical to animal populations where extensive forests are lacking. In grasslands, rangelands, and intensively farmed regions of the United States, woody vegetation along waterways is essential for survival of many wildlife populations.

Dead woody vegetation is an important component of wildlife habitat in riparian woodlands. Standing dead trees or snags provide nest sites for cavity-dwelling birds, den trees for small and medium-sized mammals, and feeding, loafing, and hunting sites for many species. Fallen logs function as cover for wildlife and as feeding and reproduction sites. Dead woody material that is partly submerged in water provides excellent habitat for aquatic, amphibious, and certain terrestrial species.

Surface water is a requirement of many wildlife species ( as an environment for feeding (e.g., waterfowl, fish-eating birds), reproduction (e.g., amphibians), travel (e.g., beaver, muskrats), and escape (e.g., amphibians, muskrat, and beaver). Consequently, many species are rarely found far from water. Thus water bodies add a dimension of habitat to riparian ecosystems.

Even in the absence of surface water, soil moisture may be ultimately responsible for major differences in species composition and productivity between riparian and upland ecosystems. Generally, moister sites are more productive of wildlife because foods (vegetation, seeds, and insects) are more abundant there, and vegetation structure is more favorable to a greater number of species. Several small mammal species (e.g., water shrew) are physiologically restricted in distribution to areas with high soil moisture. Moist soils are required by some bird species for feeding (e.g., American woodcock) and as preferred nesting habitat for others (e.g., prothonotary warbler).

Associated with most riparian ecosystems is substantial development of edge at the interface between stream channel and riparian vegetation and in the transition from floodplain to upland plant communities. The interface between stream and woody plant communities may be one of the greatest values to wildlife of riparian ecosystems because both density and diversity of species tend to be higher at this ecotone than in adjacent uplands. Many species occur almost entirely in this zone. Riparian-upland edges are also very important for many upland and edge species of wildlife, especially where woody riparian communities adjoin relatively open rangeland, grassland, or farmland.

The linear nature of riparian ecosystems provides distinct corridors that are important as migration and dispersal routes and as forested connectors between habitats for wildlife. Woody vegetation must be present for many terrestrial species to find needed cover while traveling across otherwise open areas. Animals involved in population dispersal may use food and water from riparian areas during their movements. The value of waterway corridors for migratory movements may be more accentuated in arid regions than in humid, more heavily vegetated areas.

Disturbances to Riparian Areas

Flooding and the resulting erosion and deposition are common forces that shape the riparian area. During extreme flooding, these forces can sometimes appear devastating, but in most cases the riparian area recovers rapidly. Other natural disturbance elements include fire, wind, and wildlife (i.e., beaver) alterations. Again, these elements usually help build the character of the riparian area and are not considered to have long-lasting adverse impacts.

Man-made changes, on the other hand, often do have long-term adverse effects. Hydromodification --the building of dams across channels, the construction of levees, and the channelization of the streams--may have the most adverse impacts upon riparian areas. These modifications significantly alter the hydrology that is so important to the riparian system. Hydromodifications also disrupt the continuity of the longitudinal gradient of the riparian system. Water withdrawals from streams also may reduce base flow, depriving riparian areas of needed moisture.

The most common disturbance to riparian areas involves clearing vegetation and converting the area to other uses such as cropland and urban land. Excessive logging can denude the banks of vegetation. Overgrazing can be quite devastating to riparian areas because livestock tend to congregate in riparian areas for extended periods, eat much of the vegetation, and trample streambanks. Even recreational development can destroy natural plant diversity and structure, lead to soil compaction and erosion, and disturb wildlife. It should be noted that some of these disturbance factors can be managed and the damaged riparian system will recover.

Invasion by exotic plant species (Tamarix, Elaeagnus, and Eucalyptus) can also adversely impact riparian areas by outcompeting the native vegetation. As these species become dominant in a riparian area, the overall vegetative diversity decreases. This results in less favorable habitat for most wildlife species. Not all impacts to riparian areas are caused by direct manipulation of the riparian zone. Offsite disturbances may also have significant effects. The character of a riparian area is dependent upon the condition of its watershed. Likewise, the condition of the riparian area is a reflection of the watershed.

Most important is the relationship of watershed hydrology to the riparian area. In general, the amount and type of vegetative ground cover, the areal extent of the watershed, and the slope of the terrain are directly related to the percentage of water that will enter the drainage system as surface flow or as percolated water. Riparian plant composition, habitat structure, and productivity are determined by the timing, duration, and extent of flooding. Modification of the natural dynamic regime, such as land use changes, paving areas, or vegetation removal, can lead to extended extremes of drought or flooding, with a resultant drastic decline in productivity (Manci 1989).

Riparian Evaluation Procedures

In recent years a large number of riparian classification, inventory, and evaluation procedures have been developed. Most of these were developed to fit local needs or specific programs. Some are comprehensive, requiring detailed onsite surveys; others are very general. The NRCS West National Technical Center developed a "Stream and Stream Corridor Physical Inventory" procedure and the Midwest National Technical Center developed a "Soil Bioengineering Inventory" procedure. Both of these procedures address physical features of the stream channel as well as components of the riparian area. Gebhardt et al. (1990) reviewed eleven procedures selected from a lengthy list. They are all regional or national in scope, they provide management information, and they integrate stream attributes and riparian vegetation. A brief comparison of these eleven procedures is provided in the appendix.

Current Status, Conditions, and Trends

No known comprehensive national inventory has been completed on the status, conditions, or trends of riparian areas. Local inventories have been conducted to provide information for specific needs. The U.S. Forest Service and the Bureau of Land Management routinely gather riparian information for activities on land they oversee. The U.S. Fish and Wildlife Service has been mapping riparian areas in selected areas and has published maps for New Mexico and Arizona. However, very little mapping information that is national in scope exists for private land.

Swift (1984) estimated that originally the conterminous United States had 30.3 to 40.5 million hectares (75-100 million acres) of riparian habitats and that between 10 and 14 million hectares (25-35 million acres) currently remain in the 48 conterminous states.

The 1982 National Resources Inventory (NRI) contained a section on riparian areas. Data were gathered from points that fell on riparian areas. These data included the kind of area, kind of vegetation, and width of strip. Unfortunately, this information was rarely utilized locally and never summarized nationally. The riparian category was then dropped from later NRI updates.

In 1993 the Environmental Protection Agency (EPA) began a regional assessment of riparian areas as part of the Environmental Monitoring and Assessment Program (EMAP). The study involves pilot projects on approximately 1,000 streams across the country. Assessments include the condition of instream habitat and of riparian vegetation. A summary of results from these regional pilot projects is expected to be available in May 1996, but these results are not intended to be extrapolated to represent all riparian areas. At this time no decisions have been made on expanding the EMAP effort to obtain data that will be representative of all riparian areas throughout the country.

In September 1993 NRCS conducted a survey of all NRCS State Offices to determine, among other things, estimates of the extent and quality of riparian areas. Results from that survey indicated that only three states (Oklahoma, Connecticut, and Rhode Island) had a statewide inventory of riparian areas. A fourth state (Arizona) is in the final phase of completing a riparian inventory.

In the absence of a comprehensive inventory of riparian areas, inventories of water bodies provide a rough indication of the extent and distribution of these ecosystems. One of the most widely used sets of numbers for the extent of streams and other water bodies in the United States comes from the biennial nationwide water quality report to the Congress as required under Section 305(b) of the Clean Water Act. This inventory, however, is not yet comprehensive; it is based on data reported by the states to the Environmental Protection Agency and is primarily a survey of water quality. The 1990 report indicated that 1.8 million miles of perennial streams and 39.4 million acres of lakes in the United States had been assessed for water quality (table 1). Some states added nonperennial streams, canals, and ditches to the 1992 report. This brought the total estimate of assessed rivers and streams to 3.5 million miles (table 1). It can be assumed that riparian zones of varying conditions are associated with these water bodies. It is anticipated that the 1992 NRI data will contain information on the acreage of perennial streams in different width categories.

In response to a Government Accounting Office (GAO) request for information on areas that might be involved if the Conservation Reserve Program (CRP) were to be redesigned to give priority to stream buffer areas, a team at the Agricultural Experiment Station in Temple, Texas, developed estimates of miles of streams on agricultural land by three different width classes (Clive Walker, personal communication, June 13, 1995). The team developed data from the following basic assumptions:

  • Where the 1:100,000 scale digitized line graph (DLG) maps showed lines for both banks of rivers, the rivers were assumed to be perennial.
  • Where stream lines were displayed on the 1:100,000 scale DLG maps but not on the 1:2,000,000 scale DLG maps, those streams were assumed to be perennial also but narrower than the streams identified in the first assumption.
  • Where stream lines could be found only on the 1:100,000 scale DLG maps and not on any of the smaller-scale maps, it was assumed that those small streams were all intermittent.

The total length of rivers and streams on agricultural land was estimated to be 1.07 million miles. Of this total, 13,000 miles are considered to be wide rivers, over 89,000 miles are narrow perennial streams, and over 976,000 miles are classified as intermittent streams (table 2). No attempt was made by the team to estimate the condition of riparian areas along these streams.

Brinson et al. (1981) estimated the amount of land subjected to flooding (100-year floodplain) with the potential of supporting riparian ecosystems at 121 million acres, or 6 percent of the land in the United States, excluding Alaska. In reality, much less exists in a natural or seminatural forested condition, and the authors provide a conservative estimate of 23 million acres for existing riparian vegetation. They also cite another source to estimate that about 70 percent of the original floodplain forest has been converted to urban and cultivated agricultural land uses.

Case histories of the status and condition of riparian ecosystems show large differences in loss from place to place, but as much as a 95-percent loss of natural vegetation has been reported in some areas. Examples for the lower Mississippi, Colorado, Sacramento, and Missouri Rivers have been particularly well documented and, in comparison with estimates of loss of natural vegetation in uplands, put riparian lands in the category of the most severely altered ecosystems in the country (Brinson et al. 1981).

Treatment and Management Opportunities

A number of agencies and organizations provide information and assistance to private land users on methods to protect, enhance, and restore riparian areas. This assistance includes informational and educational material on functions and values of riparian areas, planning assistance, design of practices, financial assistance through cost sharing, and direct assistance in installing practices. Practices and measures include (but are not limited to) grazing management systems, fencing, livestock watering facilities, buffer strips, tree and shrub planting, timber harvesting, installation of culverts and stream crossings, wildlife habitat management, recreational development, bank stabilization, and use of instream structures to enhance aquatic habitats.

Some of the most notable USDA programs that offer specific assistance for riparian areas on private lands are the Conservation Reserve Program (CRP), the Wetland Reserve Program (WRP), and the Stewardship Incentive Program (SIP). Many State agencies have programs targeted to riparian areas. The Pennsylvania Game Commission, for example, cooperates in the Chesapeake Bay Program with various other state agencies, conservation districts, the Cooperative Extension Service, NRCS, and the Farm Service Agency (FSA) by offering financial and technical assistance to farmers who participate in one of the commission's cooperative public-access programs. The commission purchases materials for fencing and installs the fence. Private organizations like the Izaak Walton League of America and Trout Unlimited also have programs aimed at educating the public on the importance of riparian areas and their management.


  1. Develop a national classification system and evaluation procedure for riparian areas.
    Existing riparian classification systems and evaluation procedures were developed to address specific local conditions and objectives. As these systems and procedures use different data, comparisons of results are difficult or impossible to make. A classification system and evaluation procedure designed to address national objectives will allow for a nationwide inventory of riparian conditions. Information on the extent and condition of riparian areas could then be used in developing agency policies and programs and in natural resource planning activities.
  2. Conduct a periodic national inventory of the status of riparian areas.
    At present, riparian area inventories are local or regional in nature and do not cover the entire country, and attempts to use surrogate measures (i.e., miles of streams) can provide only "ballpark" estimates of the extent of riparian areas. These indicators are of no use in determining the condition of the areas. A direct national inventory utilizing a standard classification system and evaluation procedure is the only way to obtain accurate information on the extent and condition of riparian areas. Periodic inventories, using the same protocols, will provide data that can be used to evaluate trends in the extent and condition of riparian areas.
  3. Increase the amount of research on the functions of riparian areas.
    A considerable amount of information has been gained in recent years on the functions of riparian areas, but much more is needed to support management decisions at the regional or local level. For example, much of the knowledge of riparian effects on water quality is based on research in the Southeast under very specific geologic, hydrologic, topographic, and climatic conditions. Yet little or no information of this type is known in many other regions. The water quality improvement processes in the southeastern studies may apply universally, but the effectiveness of their results may vary considerably. The need for further research generally applies to all functions of riparian areas.
  4. Improve hydrological, geomorphological, and ecological models.
    Computer models are available that make predictions on the various processes that affect riparian areas. Few of these models, however, contain functions that specifically integrate hydrological, geomorphological, or ecological relationships specific to riparian areas. Models need to be improved or developed for site-specific as well as watershed-level application.
  5. Acquire multispectral and high spatial resolution imagery to inventory and monitor riparian areas.
    Remote sensing from LANDSAT Thematic Mapper (TM) and SPOT imageries have the potential of providing excellent information on riparian communities, structure, and possibly quality that is relatively easy and time/cost-effective to obtain in comparison with traditional onsite field mapping. LANDSAT TM scenes can be used along with USGS hydrography DLG's to help map riparian ecosystems and their changes through time. Mapping of riparian areas can be improved by coupling contemporary digital orthophotography with multispectral SPOT imagery, although very narrow riparian areas would still require traditional field mapping techniques.
  6. Base riparian area management decisions on landscape needs as well as site-specific requirements.
    Direct or indirect disturbances of riparian vegetation may result in habitat conditions more conducive to a different group of wildlife species than the communities originally inhabiting the area. These species tend to be "ecological generalists" that may add to the biological diversity at the local level. The invading species, however, may also outcompete or hybridize with unique, native species and actually cause a reduction in regional biodiversity. Management, therefore, should consider the historical extensiveness and composition of the riparian area at issue and the risks involving the invading wildlife and plant species. It is of at least equal importance that management decisions should not be made exclusively at such a large scale that they tend to be off-the-shelf remedies. Once the desired riparian area condition is reached, local resource data should be used to make site-specific applications.
  7. Emphasize riparian areas in many of the natural resource conservation policies and programs.
    Riparian areas have received increased emphasis in recent years in many agency policies and programs; yet there remain many opportunities through which these efforts can be strengthened. Existing policies and programs that affect riparian areas should be evaluated to ensure that clearly stated objectives for riparian areas are included. An evaluation should also be conducted to identify weaknesses or missing elements in riparian policy and programs. Based on these results, new or revised policies, including executive orders, and programs should be proposed.

Table 1. River Miles Reported from the National Water Quality Report to Congress
  River miles assessed
State 1990 Report 1992 Report
Alabama 40,600 76,825
Alaska -- 405,400
Arizona 6,671 148,896
Arkansas 11,506 93,275
California 26,970 189,300
Colorado 14,655 27,195
Connecticut 8,400 8,118
Delaware 500 3,208
Delaware River Basin 206 206
District of Columbia 36 186
Florida 12,659 52,887
Georgia 20,000 67,567
Hawaii 349 250
Idaho -- 118,064
Illinois 14,080 34,950
Indiana 90,000 36,047
Iowa 18,300 83,192
Kansas 19,791 131,562
Kentucky 18,465 88,518
Louisiana 14,180 64,921
Maine 31,672 31,672
Maryland 9,300 17,000
Massachusetts 10,704 8,728
Michigan 36,350 56,475
Minnesota 91,944 92,680
Mississippi 15,623 83,381
Missouri 19,630 116,750
Montana 20,532 178,896
Nebraska 10,212 80,610
Nevada -- 142,700
New Hampshire 14,544 10,841
New Jersey -- 6,587
New Mexico 3,500 119,633
New York 70,000 51,729
North Carolina 37,378 37,699
North Dakota 11,284 11,912
Ohio 43,917 29,270
Ohio River Valley 981 981
Oklahoma 19,791 88,063
Oregon 90,000 90,966
Pennsylvania 50,000 55,000
Puerto Rico 5,373 5,370
Rhode Island 724 772
South Carolina 9,900 9,900
South Dakota 9,937 10,011
Tennessee 19,124 18,988
Texas 80,000 201,529
Utah -- 11,808
Vermont 5,162 5,264
Virgin Islands -- --
Virginia 27,240 54,418
Washington 40,492 40,280
West Virginia 28,361 33,044
Wisconsin -- 56,680
Wyoming 19,437 120,260
Totals 1,150,482 3,510,464
Source: U.S. Environmental Protection Agency, National Water Quality Report to Congress


Table 2. River Length Totals on Agricultural Land
State All rivers and streams, total* Perennial rivers and streams Intermittent rivers and streams
All Wide Narrow
  ------------------------ miles -------------------------
Alabama 17,166.9 1,490.4 194.2 1,296.2 15,676.5
Arizona 3,861.4 142.9 24.0 118.9 3,718.5
Arkansas 29,749.4 2,271.9 722.5 1,549.4 27,477.5
California 32,592.1 1,684.8 677.1 1,007.7 30,907.3
Colorado 19,155.2 1,469.6 167.0 1,302.6 17,685.6
Connecticut 736.8 98.2 35.9 62.3 638.5
Delaware 1,074.0 63.0 19.0 44.0 1,011.1
Florida 18,418.2 715.5 48.2 667.2 17,702.7
Georgia 13,416.3 1,519.2 178.1 1,341.1 11,897.1
Idaho 18,549.6 1,496.7 269.9 1,226.8 17,052.8
Illinois 55,778.2 6,194.0 472.9 5,721.1 49,584.2
Indiana 22,672.7 3,118.6 480.7 2,637.9 19,554.1
Iowa 61,228.1 7,303.6 521.4 6,782.2 53,924.5
Kansas 84,402.3 4,944.1 486.6 4,457.5 79,458.2
Kentucky 20,794.1 2,149.9 489.6 1,660.4 18,644.2
Louisiana 17,746.4 2,423.2 368.5 2,054.7 15,323.2
Maine** 1,494.7 184.2 200.8 0.0 1,310.5
Maryland 4,333.2 433.2 391.6 41.6 3,900.0
Massachusetts 909.0 75.9 39.4 36.5 833.1
Michigan 24,679.3 2,710.3 268.0 2,442.3 21,968.9
Minnesota 44,543.2 5,368.0 359.5 5,008.6 39,175.2
Mississippi 30,810.2 2,151.4 191.5 1,959.8 28,658.8
Missouri 61,801.2 6,948.9 444.1 6,504.7 54,852.3
Montana 33,271.1 2,756.6 457.6 2,299.0 30,514.6
Nebraska 53,291.2 4,408.2 443.2 3,965.0 48,883.1
Nevada 3,415.6 164.9 2.5 162.4 3,250.7
New Hampshire 678.9 49.0 74.1 0.0 629.9
New Jersey 1,960.0 222.7 32.7 190.0 1,737.3
New Mexico 3,561.9 276.6 86.7 189.9 3,285.3
New York 17,368.0 1,628.2 416.1 1,212.1 15,739.8
North Carolina 16,175.6 1,706.4 186.4 1,519.9 14,469.2
North Dakota 37,011.6 2,753.4 146.9 2,606.5 34,258.2
Ohio 40,001.9 3,901.2 391.0 3,510.1 36,100.7
Oklahoma 41,879.5 3,674.5 532.6 3,141.9 38,205.1
Oregon 14,915.4 1,276.3 259.5 1,016.8 13,639.1
Pennsylvania 18,452.0 1,900.2 261.1 1,639.1 16,551.8
Rhode Island** 69.1 2.0 6.2 0.0 67.1
South Carolina 6,872.6 1,031.6 106.4 925.3 5,841.0
South Dakota 42,828.6 2,554.6 132.7 2,421.9 40,273.9
Tennessee 24,898.0 1,795.8 265.4 1,530.4 23,102.2
Texas 49,554.5 5,894.4 694.8 5,199.6 43,660.1
Utah 6,636.2 440.8 30.9 409.9 6,195.4
Vermont 1,953.0 247.0 133.4 113.5 1,706.1
Virginia 13,752.1 1,239.6 435.0 804.6 12,512.5
Washington 17,396.4 1,281.8 249.1 1,032.7 16,114.6
West Virginia 4,948.6 401.3 167.9 233.4 4,547.3
Wisconsin 28,050.8 2,922.6 269.1 2,653.5 25,128.1
Wyoming 9,845.7 1,006.8 177.6 829.3 8,838.9
48 States 1,074,700.9 98,494.1 13,009.7 85,530.4 976,206.6

Source: USDA Agricultural Research Service, Texas Agricultural Experiment Station, Blackland Research Center, Temple, Texas.

* Includes all streams shown on USGS digitized line graph maps at the 1:100,000 scale.

**Discrepancies in the numbers given for these states are due to inconsistencies between the two maps used (1:100,000 and 1:2,000,000).


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Brinson, M.M., B.L. Swift, R.C. Plantico, and J.S. Barclay. 1981. Riparian ecosystems: Their ecology and status. FWS/OBS-81/17. U.S. Fish and Wildlife Service. Kearneysville, W.V. 154 pp.

Chaney, E., W. Elmore, and W.S. Platts. 1990. Livestock grazing on western riparian areas. U.S. Environmental Protection Agency. 45 pp.

Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of wetlands and deepwater habitats of the United States. FWS/OBS-79/31. U.S. Fish and Wildlife Service, Washington, D.C. 103 pp.

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Hauer, R.H. 1977. Significance of Rio Grande riparian systems upon the avifauna. In Importance, preservation and management of riparian habitat: A symposium; Tucson, Arizona, R.R. Johnson and D.A. Jones, tech. coords., pp. 165-174. U.S. Forest Service Gen. Tech. Rep. RM-43.

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Riparian Classification Comparison (Physiographic, Geologic, and Climatic Features)
Name of Classification or Description Physiographic Features Geologic Features Climatic Features
1. Standard Ecological Site Description General orientation, geomorphic landform, slope ranges, elevation ranges Specific formations, parent rock or material included Range of average and seasonal distribution of precipitation and temperature for soil and ambient air
2. Southwest Wetlands Inherent to some degree in biogeographic realm Not provided Inherent in climate zone
4. Riparian Zone Associations Provided in description Provided in description Provided in description
5. Riparian-- Wetland Sites in Montana Geomorphic landform & orientation, elevation ranges, provided in narrative Provided Provided
6. Nevada Task Force Approach Provided at ecological site description level as in (1) above
7. Riverine Riparian Habitats Provided as geologic district, land type association, and land type Provided as geologic district, land type association Provided as domain and division (Trewartha and Horn 1980)
9. Ecosystem Classification Handbook Includes geomorphic landform, valley bottom type and subtype, Horton stream order Parent material description Not provided
10.Wetlands and Deepwater Habitats General, from Bailey 1976 Not provided General, from Bailey 1976
11.Riparian Community Types Provided Provided Provided
Source: Gebhardt et al., 1990. Classifications 3 and 8 are not included here.


Riparian Classification Comparison (Soils, Water, and General Physical Features)
Name of Classification or Description Soils Features Water Features General Physical Features
1. Standard Ecological Site Description Description of major properties,associationof soils, NRCS conventions, & soil taxonomy standards Stream type as defined by Rosgen. Flow regime, surface-ground-water features Given in site description; similar to a site type
2. Southwest Wetlands Not provided Not provided Not provided
4. Riparian Zone Associations Provided Riverine systems are not specifically discussed, but water regime and fluvial process are generally covered Basic unit is riparian landform. Includes soils, fluvial process and water regime
5. Riparian--Wetland Sites in Montana Provided as standard NRCS soil taxonomy Flow regime and sub-surface features aregenerally covered Given in site description. Includes soils, fluvial processes and water regimes
6. Nevada Task Force Approach Provided in naming convention Stream type as defined by Rosgen. Moisture condition as defined by Johnson & Carothers, 1981 Provided in naming convention
------ Also provided at the ecological level of classification ------
7. Riverine Riparian Habitats Provided in land type, valley bottom units valley bottom units Described in riverine-riparian complexes and in riverine types Described at the riverine site level
9. Ecosystem Classification Handbook Uses NRCS conventions Stream type as defined by Rosgen Basic physical description is called site type
10.Wetlands and Deepwater Habitats Provided as modifiers. Uses NRCS hydric soils descriptions Identified at the sub-system level, substrate at the class and sub-class level, water persistence at the subsystem level Provided as modifiers
11.Riparian Community Types Provided, NRCS standard Not provided Provided
Source: Gebhardt et al., 1990. Classifications 3 and 8 are not included here.


Riparian Classification Comparison (Ecosystem Description, Existing Vegetation)
Name of Classification or Description Ecosystem Description Existing Vegetation
Class Subclass Dominance Composition
1. Standard Ecological Site Description Major land resource area (MLRA) given Can be derived from dominance and composition Provided Provided
2. Southwest Wetlands Inherent in bio-geographic realm, formation type, vegetation, regional formation (biome) Obtained from formation type and regional formation Series and association Provided
4. Riparian Zone Associations Provided Can be obtained from dominance information Provided Provided
5. Riparian--Wetland Sites in Montana Provided Can be used with USFWS (10) Provided Provided Provided Provided
(called formation class and subclass)
6. Nevada Task Force Approach Generally provided by land classes Provided Provided Provided Provided
--- Also provided at the ecological site level of classification ---
7. Riverine Riparian Habitats Provided Can be obtained from dominance information Provided Provided
9. Ecosystem Classification Handbook Provided Provided in range, ecosystem, and vegetation type Provided Provided
10.Wetlands and Deepwater Habitats Generally provided at system level as marine, estuarine, riverine, etc. Provided Provided Provided Not required
11.Riparian Community Types Provided     Provided Provided
Source: Gebhardt et al., 1990. Classifications 3 and 8 are not included here.


Riparian Classification Comparison (Functional Ecological Description, PNC, Ecological Units/Site, Community Type)
Name of Classification or Description Functional Ecological Description PNC Ecological Units Ecological Site Community Type
1. Standard Ecological Site Description Provided in site narrative Provided Provided Provided in site interpretation narrative
2. Southwest Wetlands Inherent to some degree at all levels Not specifically provided Association
4. Riparian Zone Associations Provided Provided Riparian association Provided
5. Riparian-- Wetland Sites in Montana Provided Provided; called habitat type, or riparian association in describing what could occur on a riparian site type Provided
6. Nevada Task Force Approach We assume a site description would accompany the site name Provided Provided Provided; called riparian community
7. Riverine Riparian Habitats Provided Provided Provided Provided
Also includes riverine-riparian complexes, which appear very useful in relating riparian and riverine sites
9. Ecosystem Classification Handbook Provided Provided; called habitat type, and a more detailed habitat type phase Provided; includes broader unit, called vegetation type, which groups similar community types
10.Wetlands and Deepwater Habitats Not included -------------------- Not required --------------------
Could be placed as modifiers
11.Riparian Community Types Provided Not given. Stable community given Not provided Provided
Source: Gebhardt et al., 1990. Classifications 3 and 8 are not included here.


Riparian Classification Comparison (Description of Procedures' Relevance to Site Mangement)
Name of Classification or Description Description of Procedures' Relevance to Site Management
1. Standard Ecological Site Description Provided in site interpretation narrative. Relates various seral stages or community types with management actions, such as grazing, wildfire, and recreation. Also provides description of water-soil interaction and related limiting factors.
2. Southwest Wetlands Not provided, but could be easily accommodated in a site description, if information on cause and effect and site correlation is collected.
4. Riparian Zone Associations Provided in site interpretation narrative. Relates various plant zone associations and community types with management actions, such as grazing, wildfire, and recreation. Also provides description (Kovalchik) of water-soil interaction and related limiting factors.
5. Riparian-- Wetland Sites in Montana Provided in site interpretation narrative. Relates various community types with management actions, such as livestock,timber, wildlife, fisheries, fire, soil management and rehabilitation opportunities, and recreational uses and considerations.
6. Nevada Task Force Approach The reference provides an example of how site management relates to the classification system. It is assumed that site management features would be included in a classification conducted by the procedure.
7. Riverine Riparian Habitats Provided in site interpretation narrative. Relates various community types with management actions, such as grazing, wildfire, recreation, etc. Also provides description of water-soil interaction and related limiting factors.
9. Ecosystem Classification Handbook The ECODATA procedure includes a number of analysis techniques specifically for management. It is assumed that site management features would be included in classification documentation produced as a part of the interpretation and analysis of the ECODATA data base.
10.Wetlands and Deepwater Habitats Not provided.
11.Riparian Community Types Some information is given on application to site management. Management information is given under succession/management sections.
Source: Gebhardt et al., 1990. Classifications 3 and 8 are not included here.

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