Benefits and Values

Mayfly – an aquatic insect.

Riparian systems support high levels of biological diversity (Motroni 1980) and are among the most endangered ecosystems in the United States (NRC 1992). Native riparian plant communities comprise some of the most productive wildlife habitat in North America (Motroni 1980) and are critically important to the life cycle of endangered salmonid species (FISRWG 1998). Aquatic macroinvertebrates, required prey of salmonids, are correlated with healthy riparian forests. Riparian habitat supports over three quarters of the amphibians and half of the reptiles in California (Warner and Hendrix 1984).

Tiger salamanders can be found in riparian areas. Photo courtesy of Gary Nafis and CaliforniaHerps.com.

Furthermore, bird species diversity is highest in riparian habitat (Leymon 1984), which is also critical habitat for neo-tropical migrant species which utilize riparian corridors as resting, foraging, and breeding grounds. Of the 502 native species of land mammals in California, approximately 25 percent are limited to or dependent upon riparian and other wetland communities. In addition, riparian systems provide habitat for over half of the species officially listed as threatened or endangered in California and are responsible for the regulation of critical ecosystem functions in adjacent aquatic environments.

Riparian corridors are dynamic, disturbance-driven ecosystems, with hydrologic processes acting as a major force in determining terrestrial plant distribution and diversity. The total species richness bears a strong relationship to the variability, quality, and distribution of the different habitat types present. Riparian zones in a near-natural state contain a relatively high diversity of landforms, vegetation types, and successional stages that are concentrated within a small geographic area. It is important to realize that under natural conditions most of the habitat diversity originates from, and is sustained by, the high frequency of flooding and erosive disturbance caused by streams. They are especially attractive to wildlife because an adequate mix of habitat types, food, and shelter is consistently available even in the face of unpredictable natural disturbances such as drought, wildfires, or severe floods.

Mountain lions use riparian areas for hunting and as movement corridors.

Typically, the total number of plant and animal species living in riparian zone habitats is greater than in the adjacent upland habitats. This is seasonally increased by the fact that river valleys provide one of the most important routes for the yearly migratory movements of aquatic, terrestrial, and aerial animals.

Riparian vegetation provides several important physical functions that support aquatic biodiversity:

• stabilize stream banks, controlling sediment input and bank erosion
• shade river channels, thereby maintaining low water temperatures and regulating dissolved oxygen levels
• contribute substantial quantities of large woody debris to the aquatic system, providing in-stream complexity essential for the success of insects, amphibians, reptiles, and fish
• deposit large amounts of leaf litter, insects, and nutrients that are crucial for the viability of aquatic food webs
• reduce damage caused during flood events by preventing large woody debris from entering agricultural lands, roads, and properties during flood peaks.

Riparian trees along Scott Creek provide in-stream structure.

Riparian vegetation also provides important "ecosystem services," including sequestering pollutants and excess nutrients entering streams from surrounding landscapes. These effects are so great that regulatory agencies are increasingly recognizing that effective management of aquatic ecosystems requires effective management of the terrestrial plant communities that border these environments.

References

Federal Interagency Stream Restoration Working Group (FISRWG). 1998. "Stream Corridor Restoration: Principles, Processes, and Practices." Federal Interagency Stream Restoration Working Group (FISRWG). GPO Item No. 0120-A; SuDocs No. A 57.6/2:EN 3/PT.653. ISBN-0-934213-59-3. View on-line document.

Leymon, S. 1984. Seasonal Variation of Bird Numbers in a Riparian Forest, Sacramento Valley, California. In California Riparian Systems: Ecology, Conservation, and Productive Management, edited by R. E. Werner and K. M. Hendrix: University of California Press. Berkeley, California.

Motroni, R. 1980. "The Importance of Riparian Zones to Terrestrial Wildlife." US Fish and Wildlife Service.

National Research Council (NRC). 1992. "Restoration of Aquatic Ecosystems: Science, Technology and Public Policy." Committee on Restoration of Aquatic Systems. National Academy Press. View on-line source.

Warner, R.E., and K.M. Hendrix. 1984. California Riparian Systems. Ecology, Conservation, and Productive Management. Berkeley and Los Angeles, CA: University of California Press.

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