Riparian corridors in the California Central Coast Region

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An environmental summary created by the ENVS 560/L Watershed Systems class at CSUMB.


Riparian corridors encompass both riparian zones and the adjacent terrestrial ecosystems that protect or influence the riparian zone[1].

A riparian zone [2] is a strip of land whose physical and biological character is overwhelmingly determined by its proximity to a body of running water. Riparian zones can exist along both perennial and seasonally flowing water-bodies.

Riparian corridors are important in California's Central Coast Region because they serve as wildlife corridors for local fauna, provide flood, erosion and temperature control, and help maintain water quality. The topography and the mixed land use in the region makes riparian corridors crucial for supporting surrounding ecosystems.

There are several substantial threats to riparian corridors in the Central California Coast region that are shared with other areas of the West. These include impacts from urbanization and development, drought, and groundwater extraction. [3]


An example of a threatened riparian corridor of local importance is the Salinas river corridor in the Monterey Bay region. The Salinas Valley is a broad alluvial plain[4] of intense agricultural activity defined by three distinct coastal ranges: the Santa Cruz Mountains to the north, the Gabilan Range to the east, and the Santa Lucia Range to the south. Maintaining connectivity between these ranges is an important conservation measure for species with large territorial requirements. Because most land use is agricultural, pathways for wildlife are focused along waterway channels and riparian habitats. Another example is the corridor of the Pajaro River, which flows through agricultural areas just south of the City of Watsonville. Similarly, the Gabilan Creek corridor crosses through agricultural areas, but also through the center of the city of Salinas, joining Alisal Creek and Natividad Creek in the middle of Carr Lake.

In 2015, the Monterey County Planning Commission made amendments to the 2010 Monterey County General Plan to establish an ordinance requiring biological studies for developments near riparian corridors and wildlife linkages. A consulting group, Pathways for Wildlife, created a county-wide map of wildlife corridors and linkages (using these methods) to be used as the basis for the ordinance.

Biophysical Context

Riparian corridors generally exist as one component with many features. Oftentimes, their composition is influenced by human interaction. Riparian corridors provide a variety of environmental and ecological benefits:

  • Biodiversity In theory, riparian corridors conserve biodiversity by ensuring that species have the ability to migrate, colonize, and interbreed. Migration refers to a species' seasonal movements. Riparian corridors connect habitat utilized by migratory species at different times of the year. Colonization refers to population establishment. Riparian corridors enable species to colonize new areas when local resources have been exhausted. Interbreeding refers to the exchange of genetic information between disparate individuals and populations. Riparian corridors conserve genetic diversity by maintaining access to a larger gene pool. There is a growing body of evidence that riparian corridors facilitate biodiversity [5], and buffered zones around streams facilitate movements of animals such as black bears and forest dependent birds[6].
  • Streambank stability Fast-growing riparian plants with vigorous root systems, such as willows and alders, thrive in floodplain conditions. Riparian vegetation controls erosion, stabilizes banks, and influences sediment deposition[7].
  • Flood control Riparian vegetation slows the flow of water, allowing more water to percolate into groundwater aquifers and reduce flooding downstream[7].
  • Temperature regulation Riparian corridors provide a buffer of vegetation in the riparian zone that provides shade and facilitates stable stream temperatures[8].

Riparian plants

Riparian plants include a combination of trees, shrubs, herbs, sedges/rushes, ferns, and aquatic plants. Some of the most common native species in the California central coast region are listed below [1]:

  • Trees - alders (Alnus spp.), willows (Salix spp.), cottonwoods (Populus spp.), bigleaf maple (Acer macrophyllum), California sycamore (Plantanus racemosa)
  • Shrubs - mulefat (Baccharis salicifolia), poison oak (Toxicodendron diversilobum), dogwood (Cornus spp.), snowberry (Symphoricarpos albus var. laevigata)
  • Vines - California blackberry (Rubus ursinus), Virgin's bower (Clematis ligusticifolia)
  • Herbs - California mugwort (Artemisia douglasiana), cattails (Typha spp.), stinging nettle (Urtica dioica)
  • Sedges/rushes - tule (Schoenoplectus acutus var. occidentalis), Santa Barbara sedge (Carex barbarae), spreading rush (Juncus patens)
  • Ferns - five finger fern (Adiantum aleuticum), maidenhair fern (Adiantum capillus-veneris), common lady fern (Athyrium filix-femina), giant horsetail (Equisetum telmateia)
  • Aquatic plants - duckweed (Lemna spp.), watercress (Nasturtium officinale)

Wildlife Usage

  • Mammals
    • Hilty and Merenlender (2004) found that mammalian predators in northern California were 11 times more likely to be found in riparian habitats then in the upland vineyards[9].
    • Olimpi (2017) found that in areas with intensive agriculture, even highly degraded riparian corridors provide important habitat for bats.[10]
  • Birds
    • Riparian areas provide important breeding, overwintering, foraging, and resting habitats for migratory birds in California and the arid West [11].
  • Reptiles and amphibians
    • California red-legged frogs (Rana draytonii) are known to utilize riparian corridors for foraging, dispersal, and cover.[12]

Environmental Issues

  • Water quality
  • Habitat loss
    • Gennet et al. (2013) [13] described the elimination of 13.3% of the remaining riparian habitat in the Salinas Valley in the name of food safety. The impacts to riparian corridors followed an outbreak of E. coli linked to the most productive crop in the region. The study argued that if similar practices were carried out throughout the state, as much as 40% of riparian habitat and 45% of wetlands could be affected.
  • Invasive species


Individuals and organizations that typically have a stake or interest in the management of riparian corridors in the California Central Coast Region include:

Laws, Policies, & Regulations

A variety of California laws, policies, and regulations are in place for the protection of riparian areas:

  • Wetlands and Waters of the U.S., which may occur within riparian corridors, are protected by the Environmental Protection Agency and U.S. Army Corps of Engineers under Section 404 of the Clean Water Act.
  • The Regional Water Quality Control Board regulates discharge of dredged or fill material into waters of the U.S. under Section 401 of the Clean Water Act. Regulated areas include riparian areas and wetlands
  • California Assembly Bill No. 2785 [2](approved by Gov. Schwarzenegger Sep 26, 2008) revises the Significant Natural Areas Program "to investigate, study, and identify those areas in the state that are most essential as wildlife corridors and habitat linkages and prioritize vegetative data development in those areas". The funds would be provided by the Wildlife Conservation Board from the monies made available by The Safe Drinking Water, Water Quality and Supply, Flood Control, River and Coastal protection Bond Act of 2006.
  • The Natural Community Conservation Planning (NCCP) Act of 1991 (AB 2172) provides for multi-species habitat conservation planning (MSHCP), which is recognized as an effective way to preserve the species while minimizing economic disruptions. Several MSHCP’s have been developed in California, with the cooperation of developers, federal and state agencies, and local communities. Different habitats including riparian zones and species can be protected under MSHCPs.
  • Recent food safety recommendations for agriculture in the Salinas Valley identified riparian habitat as food safety hazards. Vegetable retailers have pressured shippers and processors, which in turn have pressured farm operations to remove riparian vegetation in order to continue contracts. In addition, the practice of installing deer fences has greatly increased along the Salinas river and other areas bordering habitat due to food safety concerns.
  • Legalization of Cannabis has prompted new regulations enforced by the Regional Water Quality Control Board. These regulations dictate the required setbacks of Cannabis cultivation operations from riparian corridors and wetlands. [14]


Several different models are used in establishing corridors and determining connectivity: least cost path modeling, individual based movement models, graph theory, spatially explicit population models, circuit theory, and network flow models.

Future Research

It is difficult to conclude from the few studies completed whether all riparian habitats facilitate connectivity. Some suggested topics for future study of riparian corridors include:

  • A M.S. thesis on wildlife presence/absence across different habitats/landscapes in the Salinas Valley could reveal habitat connectivity provided by local waterways.
  • A thorough monitoring program of the California Central Coast waterways would give a good understanding of which characteristics of riparian zones and surrounding landscapes facilitate connectivity. There is a growing concern about maintaining connectivity between the Santa Lucia range and the Gabilan Range across the Salinas valley. It is very likely that waterways are being utilized by wide ranging species to cross the Salinas valley, but there is no documentation to support this theory. Automatic photo-monitoring could establish frequency of use of corridors by different animals. A useful thesis would be an economic cost-feasibility study of different methods to establish connectivity, and easements or lands that might be available for such a purpose.



  1. USDA Forest Service. Appendix I - Delineation of Riparian Areas, Riparian Corridors and Stream Types
  2. Wikipedia article on riparian zones
  3. Threats to riparian ecosystems in the West, a bibliography
  4. Article on the Watsonville plain
  5. Peer-reviewed article on corridors
  6. Harris LD, Hoctor T, Maehr D, Sanderson J. 1996. The role of networks and corridors in enhancing the value and protection of parks and equivalent areas. In national parks and protected areas, ed Wright RG, pages 173-197. Cambridge, England: Blackwell Science.
  7. 7.0 7.1 FEMA. 1996. Protecting floodplain resources: a guidebook for communities.
  8. Sweeny BW, Newbold JD. 2014. Streamside forest buffer width needed to protect stream water quality, habitat, and organisms: a literature review. Journal of the American Water Resources Association 50(3): 560-584.
  9. Hilty JA, Marenelender AM. 2004. Use of riparian corridors and vineyards by mammalian predators in northern California. Conservation Biology 18:126-135.
  10. Olimpi EM. 2017. Bat ecology and conservation in agricultural landscapes in the California Central Coast
  11. RHJV. 2004. The riparian bird conservation strategy for reversing the decline of riparian associated birds in California
  12. U.S. Fish & Wildlife Service. 2002. Recovery plan for the California red legged frog.
  13. Gennet S, Howard J, Langholz J, Andrews K, Reynolds MD, Morrison SA. 2013. Farm practices for food safety: an emerging threat to floodplain and riparian systems. Frontiers in Ecology and the Environment 11(5): 236-242.
  14. State Water Resources Control Board, Order WQ 2017-0023-DWQ.

Additional Resources


External Links


This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.