Written by Mindy Pratt, Utah State University
The term “riparian” is defined as vegetation, habitats, or ecosystems that are associated with bodies of water (streams or lakes)) or are dependent on the existence of perennial, intermittent, or ephemeral surface or subsurface water drainage.
Put more simply, riparian areas are the green ribbons of trees, shrubs, and grasses growing along water-courses. For example, the cottonwood groves where we like to picnic along sandy river beds, the green, shady areas next to the stream where we like to fish, and the stream edges with tadpoles and dragonflies are among the riparian features we enjoy.
Riparian areas occur in a wide range of climatic, hydrologic and ecological environments. Different latitudes and altitudes can support very different riparian communities. This is caused primarily by changes in precipitation and temperature. In the western United States, you can find riparian areas everywhere from high elevation montane forests through intermediate-elevation woodlands to low-elevation shrublands and desert grasslands.
Riparian areas are ecosystems. An ecosystem is a functional system that includes both a biotic part in the organisms, such as the plants and animals, and an abiotic part which factors in their immediate environment such as soil and topography. These organisms interact both with each other and with their environment. Each ecosystem is unique because the organisms and the environment differ significantly from other ecosystems.
The three main characteristics that define riparian area ecosystems are hydrology, soils and vegetation. These reflect the influence of additional moisture compared to the adjacent, drier uplands. Riparian areas are the transition zones, or ecotones, between aquatic (water-based) systems and terrestrial (land-based) systems, and usually have characteristics of both. These characteristics and location make it habitat for a larger number of species of plants and animals.
Because riparian areas are at the margin between water and land, their soil was most likely deposited by water and could be washed away by water. Protecting soil, streambanks, or water edges from excess erosion is an important function of riparian plants. Thus, properly functioning riparian areas absorb the water, nutrients, and energy from big events and use them to recover from disturbances while improving water quality. The toughness of riparian plants with dense, strong root systems, stems that slow floodwaters, and maybe woody debris that forms pools, adds to riparian stability and habitat diversity.
Some riparian areas, especialy those not functioning properly or in high energy - high sediment locations are very dynamic and disturbance-driven. Plant communities may be susceptible to rapid change, if soil and water conditions change dramatically. These changes might include:
Riparian areas are found at every elevation and in all landforms, and differ depending on local physical conditions (water, soil, temperature, etc.) and their location (elevation, valleys, canyons, etc.). High mountain riparian areas may be narrow and in deep ravines or canyons, while lowland floodplains in wide valleys may have large meanders. Desert washes may be sandy and only have water for a short time each year. These differences in vegetation, landform, and geology have led to a wide variety of terms used to denote riparian areas. These include riparian buffer zones, cottonwood floodplains, alluvial floodplains, floodplain forests, bosque woodlands, cienegas, and meadows.
Significant differences in water availability due to precipitation between the eastern and western United States has led to major differences in these regions’ riparian areas (See Figure 1). In the eastern United States, precipitation is much greater and riparian areas can maintain more lush vegetation than the arid regions of the western United States. Because of the higher precipitation received in the eastern United States, even the terrestrial upland ecosystems can maintain lush vegetation. As a result, it is difficult to define the boundaries between riparian areas and terrestrial uplands in the eastern United States. In contrast, in most of the western United States and particularly in the southwest, the transition between riparian and upland terrestrial systems is easily identifiable. This distinction is abrupt because the surrounding terrestrial habitat is much drier than the riparian area (Figure 1). Riparian areas in the arid western United States have different plant composition but are also more lush than their adjacent uplands. Another important difference between the eastern and western United States that influences riparian areas are the pathways that water follows to reach streams. In the eastern United States, more water infiltrates the soil resulting in more subsurface flow reaching the stream and thus, more soil moisture (Figure 1). In the western United States, there is more overland flow reaching the stream (Figure 1).
Although riparian areas can differ greatly, they all have several things in commons. They are shadier, cooler, and moister than the adjacent upland environments. A wide variety of animals are attracted to these areas including insects, amphibians, reptiles, fish, birds, and mammals. Suitable habitat (food, water, and shelter) is often provided in riparian areas to support these animals which may not occur in surrounding drier areas.
In the western United States, riparian areas compromise less than 1 percent of the land area, but they are among the most productive and valuable natural resources, rivaling our best agricultural lands. They are particularly efficient at storing water, dissipating flow energies, improving water quality, trapping sediment, building and maintaining banks, and converting of solar energy. Such an important resource requires awareness on our part, and a need to learn and understand the landscapes around us.
Riparian Area Basics - How do we classify and manage riparian areas?
Riparian Health - What makes a healthy riparian area and why does it matter?
Arizona Riparian Council. 1994. Riparian. Arizona Riparian Council Fact Sheet No. 1.
Chaney, E., W. Elmore, W.S. Platts. July 1993. Managing Change. U.S. Environmental Protection Agency.
Marti, E., S.G. Fisher, J.D. Schade and N.B. Grimm. 2000. Flood frequency and stream-riparian linkages in arid lands. In: Jones, J.B. and P.J. Mulholland (eds.), Streams and Ground Water. Academic Press. New York, NY. pp. 111-136.
Surber, G., B. Ehrhart. 1998. Stream and Riparian Areas Management: A Home Study Course for Managers. Montana State Extension Service. Information also available at http://www.animalrangeextension.montana.edu/riparianmgt/index.htm
USDA-NRCS. August 1996. Riparian Areas Environmental Uniqueness, Functions, and Values. RCA Issue Brief #11.
Zaimes G. 2007. Defining Arizona's Riparian Areas and their Importance to the Landscape. In: Zaimes G. (editor), Understanding Arizona's Riparian Areas. Univeristy of Arizona Cooperative Extension, Publication # AZ1432. pp.1-13. Available at: http://cals.arizona.edu/pubs/natresources/az1432.pdf.