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What makes California's riparian areas special?

Riparian habitats, especially in California, have high levels of biodiversity and provide habitat for many different species. Birds are by far the most diverse group in riparian zones. In California, over 135 species of birds depend on this ecosystem during at least some part of their life history. Even if species do not spend their entire lives here, many use rivers and the surrounding vegetation as vital migration routes. Riparian forests in California are by some estimations the most diverse habitat in the state in terms of wildlife (Smith 1980). These high levels of diversity are supported by the wide variety of niches made available by complex vegetation systems (ranging anywhere from grasses, shrubs to trees), as well as the widespread availability of water.

Adaptations

Riparian areas are adapted to varying water levels, ranging from flooding to drought. Both plants and animals must be able to tolerate and survive the river's fluctuations. Near the river, plants grow that cannot survive droughts but tolerate flooding. In the low riparian zone, fast-growing woody plants often grow that are adapted to extreme disturbances. Plants may either have flexible branches to go with the flow of the river, or brittle branches that are sacrificed for the health of the entire plant. In the middle zone, you may find bunchgrasses and shrubs that prefer moist soils, and on the upper banks, drought-resistant plants with long tap roots that reach into the groundwater supply.

In riparian zones, natural floods can uproot entire forests and create new river paths entirely. Therefore, it is also vital that plants can successfully re-colonize after disturbances. Unfortunately, this quick turnover can also leave areas open and vulnerable to the spread of invasives. Some plant strategies for living in riparian areas include:

Propagule floating, where plants send seeds down streams for long-distance dispersal and colonization
Low density tissue, pits/hair, and waxy epidermis that help seeds float
Seeds often tolerant of passing through fish digestive systems
Riparian plants have many adaptations protecting them against floods and the lack of oxygen that can come with them, even including underwater photosynthesis or other energy productions in the absence of oxygen
Often, plants are smaller and even have built-in breaking points on their branches to reduce mechanical stress from water

Common Species

Photo: Cheryl Reynolds

Beaver

Castor canadensis

Second largest rodent in the world
Historically found throughout North America
Very important ecosystem engineers
Use their giant incisors to cut down trees to build dams and shelters

Photo: SMMTC

California Mugwort

Artemisia douglasiana

Native to streambanks and tolerates seasonal flooding
Helpful for bank stabilization and erosion prevention
May alleviate effects of poison oak by rubbing leaves on affected area

Photo: Wikimedia Commons

Yellow Warbler

Setophaga petechia

Nest on shrubs near streams
Thrive with diversity of insects to eat
Cattle grazing can degrade their nesting habitats, especially willow stands along creeks
Brown-headed Cowbirds lay eggs in their nests and can be detrimental to breeding success

Photo: Nature Hills Nursery

Boxelder Maple

Acer negundo

Often found by streams, but can develop drought tolerance if the roots grow deep enough
Attractive to many beneficial insects
Beautiful fall colors

Photo: Woodbrook Native Plant Nursery

Pacific Willow

Salix lucida

Helps stabilize stream banks
Can extend roots and spread to areas with proper moisture
Produce salicin, a compound similar to aspirin- chewing the bark can help alleviate pain

Photo: Wikimedia Commons

California Black Walnut

Juglans californica

Native to Southern California
Provides food for birds and small animals
Important food source for the Chumash people

Photo: David A. Hofmann/Flickr

Blue Elderberry

Sambucus cerulea

Vital food for birds in riparian areas
Obligate food source of the Valley Elderberry Longhorn Beetle

Photo: Graham Owen

California Golden Trout

Oncorhynchus aguabonita

Popular for fishing, the golden trout has been extensively stocked in rivers throughout CA
Their coloration helps them blend in and hide from predators

Sit back and enjoy an adventure into the High Sierra in search of California Golden Trout, from the comfort of your own home.

Rarer Sights

Photo: USFWS

Southern California Steelhead Trout

Oncorhynchus mykiss

Blocked from accessing 90% of their habitat due to dams and other development, making them unable to reproduce in the rivers in which they were born

Photo: NPS / Will Elder

California Red-legged Frog

Rana draytonii

Largest native frog in Western U.S.
Threatened by loss of habitat
Need breeding sites that are moist throughout summer
Like slow-moving streams and shady banks where they are protected from excess heat
Preyed upon by the invasive American bullfrog
Adults will eat many things from invertebrates to small amphibians and mammals

Photo: RCA Associates

Riparian Brush Rabbit

Sylvilagus bachmani riparius

One of the most endangered species in California
One of 8 subspecies
Endangered due to loss of more than 90% of riparian habitat in the Central Valley

Photo: Scarlett Howell/USGS

Southwestern Willow Flycatcher

Empidonax traillii extimus

Frequently nests in nonnative tamarisk and native willows
Endangered due to habitat loss and fragmentation
Important indicator species
Can evade Brown-headed cowbird parasitism by burying cowbird eggs laid in their nests or even building new nests on top of them

Photo: FWS

Valley Elderberry Longhorn Beetle

Desmocerus californicus dimorphus

Threatened since 1980 due to loss of habitat
Both larvae and adults feed solely on elderberry

Photo: Robert Hamilton

Least Bell's Vireo

Vireo bellii pusillus

Federally endangered, used to be common in CA for breeding
Only 300 pairs when listed in 1986
About half of their current population occurs on Camp Pendleton Marine Corps Base in San Diego County

Photo: Becky Matsubara/Flickr

Swainsons Hawk

Buteo Swainsoni

Listed as threatened in CA in 1983
Populations very slowly increasing, with largest concentrations in the Central Valley
Nest in cottonwood or valley oak

Photo: Audobon Society

Yellow-Billed Cuckoo

Coccycus americanus

Forage and breed in cottonwood and willow trees
Prefer sites with dense understory vegetation, so are affected by cattle grazing

Invasive Species

Photo: Wikipedia

Giant Reed

Arundo donax

Occurs in Central and Southern California
Increase chances of and spread of fires
Forms massive stands that block out native wildlife
Reduces habitat and insect food supply for native birds by as much as half
Provides little shade for rivers and harms streams and fish by increasing water temperatures

Photo: Gary Nafis

Common Watersnake

Nerodia sipedon

Native to eastern US
Likely introduced as released pets
Directly prey on native amphibians and fish
Competes with native garter snakes, including the threatened Giant Garter Snake

Photo: Musat/Getty Images/iStockphoto

Tamarisk/Salt Cedar

Tamarix sp.

Native to Asia
Poor habitat for birds
May increase erosion and salinity
Promotes fire and can reprout at the base
Feathery appearance

Photo: Wikipedia

American Bullfrog

Intentionally introduced for insect control and commonly escape from other sources
Outcompetes and preys upon native red-legged frog
Carrier of deadly chytrid fungus which has caused the extinction of over 100 species since the 1970's

Tamarisk and Arundo (Giant Reed) are known as the "Deadly Duo." They establish in similar habitats and often while one is being removed in conservation efforts, the other will take over.

Photo: LA Vector Control District

Mosquitofish

Gambusia affinis

Introduced in 1992 for mosquito control
Adapted to eat larvae of mosquitoes, but in California eat larvae of native fish and insects as well
Aggressive to other, even larger, native fish

Photo: Alex Wild

Argentine Ant

Linepithema humile

Can easily entirely outcompete most native ant species
Diminish native ant food source for native reptiles
Thrive in California's moist riparian areas

Photo: U.S. Geological Survey

Red Swamp Crayfish

Procambarus clarkii

Native to Southern US
Prey on threatened Red-legged frog
Kill dragonfly larvae which as adults naturally control mosquito populations, while crayfish are not as effective at eating larvae
May increase transmission of disease

Photo: PlantRight

Mexican Fan Palm

Washingtonia robusta

Common ornamental that has invaded riparian areas
Grows in dense stands that can outcompete natives
Dead fronds can easily catch and spread fire

For more information on California invasives, visit https://wildlife.ca.gov/Conservation/Invasives/Species .

Fish Species

Visit the UC Davis California Fish Species website to find out more about fish by location and the current research being done!

References

Header Photo: California. (n.d.). Retrieved May 27, 2020, from https://www.americanrivers.org/region/california/
Admin. (2020, February 3). Endangered Species in California - RCA Associates, Inc. Retrieved from http://www.rcaassociatesllc.com/species/endangered-species-in-california/
California Invasive Plant Council. (2018, March 15). Washingtonia robusta Profile. Retrieved from https://www.cal-ipc.org/plants/profile/washingtonia-robusta-profile/#:~:text=Mexican fan palm is a,can create a fire hazard.
California Wildlife Conservation Board. (2020). California Riparian Habitat Conservation Program. Retrieved from https://wcb.ca.gov/Programs/Riparian
Calscape. (n.d.). Box Elder, Acer negundo. Retrieved from https://calscape.org/Acer-negundo-(Box-Elder)?srchcr=sc5ad5c3e302646
Calscape. (n.d.). Southern California Black Walnut, Juglans californica. Retrieved from https://calscape.org/Juglans-californica-(Southern-California-Black-Walnut)?srchcr=sc5841b857b3fff
Catford, J. A., & Jansson, R. (2014, June 19). Drowned, buried and carried away: Effects of plant traits on the distribution of native and alien species in riparian ecosystems. Retrieved from https://www.researchgate.net/publication/264351202_Drowned_buried_and_carried_away_Effects_of_plant_traits_on_the_distribution_of_native_and_alien_species_in_riparian_ecosystems
CDFW. (2020). California's Invaders: American Bullfrog. Retrieved from https://wildlife.ca.gov/Conservation/Invasives/Species/Bullfrog#:~:text=American bullfrogs were intentionally introduced,some areas during fish stocking.
CDFW. (2020, June 8). California Golden Trout. Retrieved from https://wildlife.ca.gov/Conservation/Fishes/California-Golden-Trout
CDFW. (2020). California's Invaders: Northern Watersnake. Retrieved from https://wildlife.ca.gov/Conservation/Invasives/Species/Northern-Watersnake#:~:text=Northern watersnakes are heavy-bodied,4 ½ feet in length.&text=Older northern watersnakes often appear,smelling musk mixed with feces.
CDFW. (2020). Swainson's Hawks in California. Retrieved from https://wildlife.ca.gov/Conservation/Birds/Swainson-Hawks
Clarke, C. (2016, February 17). Invasive Species Week: The Argentine Ant. Retrieved from https://www.kcet.org/redefine/invasive-species-week-the-argentine-ant
Colgan, D. (2018, August 6). Invasive crayfish lead to more mosquitoes and risk of disease in Southern California. Retrieved from https://newsroom.ucla.edu/releases/invasive-crayfish-lead-to-more-mosquitoes-and-risk-of-disease-in-southern-california
Cornell Lab of Ornithology. (2019). Yellow Warbler Life History, All About Birds. Retrieved from https://www.allaboutbirds.org/guide/Yellow_Warbler/lifehistory#:~:text=Backyard Tips,nesting habitat for these birds.
Cornell Lab of Ornithology. (2019). Willow Flycatcher Overview, All About Birds. Retrieved from https://www.allaboutbirds.org/guide/Willow_Flycatcher/overview
Davison, V., External Affairs Divison, & Sacramento Fish & Wildlife Office. (2017, December 6). Riparian Brush Rabbit Recovery: Sacramento Fish & Wildlife Office. Retrieved from https://www.fws.gov/sacramento/es/Recovery-Planning/Riparian-Brush-Rabbits/
Davison, V., External Affairs Division, & Sacramento Fish & Wildlife Office. (2017, November 30). Western Yellow-billed Cuckoo - Birds, Endangered Species Accounts. Retrieved from https://www.fws.gov/sacramento/es_species/Accounts/Birds/yellow_billed_cuckoo/
Dudley, T. (2017, October 16). IPCW Plant Report: Arundo donax. Retrieved from https://www.cal-ipc.org/resources/library/publications/ipcw/report8/#:~:text=Giant reed occurs in central,the Sacramento and San Joaquin
Kadlec, M. 2003. "Dendroica petechia" (On-line), Animal Diversity Web. Accessed June 09, 2020 at https://animaldiversity.org/accounts/Dendroica_petechia/
Kelso, M. (n.d.). CHAPTER 11: NATIVE PLANT ADAPTATIONS TO FLOW IN GRAND CANYON. Retrieved from https://watershed.ucdavis.edu/education/classes/files/content/page/Ch11_NativePlantAdaptations_Kelso.pdf
Kus, B. 2002. Least Bell's Vireo (Vireo bellii pusillus). In The Riparian Bird Conservation Plan: a strategy for reversing the decline of riparian-associated birds in California. California Partners in Flight. http://www.prbo.org/calpif/htmldocs/riparian_v-2.html
Moore, L. M. (2003, January 29). Plant Guide - Pacific Willow. Retrieved from https://plants.usda.gov/plantguide/pdf/cs_salul.pdf
National Parks Service. (2020, April 27). California Red-legged Frogs. Retrieved from https://www.nps.gov/rlc/pacificcoast/california-red-legged-frogs.htm
The National Wildlife Federation. (n.d.). California Red-Legged Frog. Retrieved from https://www.nwf.org/Educational-Resources/Wildlife-Guide/Amphibians/California-Red-Legged-Frog
Nico, L., Fuller, P., Jacobs, G., Cannister, M., Larson, J., Fusaro, A., Makled, T.H., and Neilson, M.E., 2020, Gambusia affinis (Baird and Girard, 1853): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=846, Revision Date: 4/10/2020, Peer Review Date: 1/25/2016, Access Date: 6/9/2020
Riparian Invasion Research Laboratory. (2012). Tamarisk in California. Retrieved from http://rivrlab.msi.ucsb.edu/california-alliance-tamarisk-biocontrol/tamarisk-california
USDA Natural Resources Conservation Service. (1996). Natural Resources Conservation Service. Retrieved from https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/technical/?cid=nrcs143_014199
Ventura County Planning Department, Ventura, California. (2006). Guide to Native and Invasive Streamside Plants: Restoring Riparian Habitats in Ventura County & along the Santa Clara River in Los Angeles County. Retrieved from http://parkway.scrwatershed.org/wkb/scrbiblio/vcpd2006.html
Wilson, B., & Wilson, C. (2014, January 25). Artemisia douglasiana, Mugwort. Retrieved from https://www.laspilitas.com/nature-of-california/plants/776--artemisia-douglasiana#:~:text=California Mugwort, Artemisia douglasiana, is,too much right above you.

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