amphibian use of chehalis river floodplain wetlands

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  • Amphibian Use of Chehalis River Floodplain WetlandsAuthor(s): Julie A. Henning and Greg SchiratoSource: Northwestern Naturalist, Vol. 87, No. 3 (Winter, 2006), pp. 209-214Published by: Society for Northwestern Vertebrate BiologyStable URL: .Accessed: 12/06/2014 23:18

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    Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331- 3803;


    Washington Department of Fish and Wildlife, 48 Devonshire Road, Montesano, Washington 98563

    ABSTRACT-The use of isolated emergent wetlands by amphibians has been well documented.

    However, amphibian habitats such as emergent wetlands in floodplains may differ from isolated wetlands because of their high disturbance (water fluctuation) related to riverine flooding, pres- ence of fish species, and increased connectivity among aquatic habitats. We compared the am-

    phibian assemblages at 6 freshwater wetland habitats in the Chehalis River floodplain and ex- amined the effect of wetland restoration on amphibians. We sampled 6 wetlands during the

    breeding season in 2003 and 2004 and captured over 15,000 adults, tadpoles, and larvae from 6 species. The red-legged frog (Rana aurora) was the most abundant species captured. The rough skinned newt (Taricha granulose) was the only amphibian captured at all sampled sites. Although it is more desirable to prevent wetland degradation from occurring, restored and enhanced wet- lands in floodplains do provide breeding habitat for amphibians. Amphibian species captured in reference wetlands were also captured in restored wetlands. Water control structures, which were used to facilitate wetland restoration, did not seem to influence utilization by amphibians; however, hydroperiod seemed to affect amphibian abundances. Wetlands with intermediate hy- droperiods had the highest amphibian abundance compared to wetlands with temporary or

    permanent water. Fish were captured in all wetlands, and those with the greatest abundance of native non-game fishes had the highest abundance of amphibians. Our results suggest that

    emergent wetlands in floodplains are dynamic habitats that can offer breeding opportunities, but microhabitat suitability needs to be considered when managing amphibian habitats.

    Key words: red-legged frog, Rana aurora, Pacific treefrog, Pseudacris regilla, bullfrog, Rana ca- tesbeiana, rough-skinned newt, Taricha granulosa, northwestern salamander, Ambystoma gracile, long-toed salamander, Ambystoma macrodactylum, amphibians, wetlands, floodplains, restora-

    tion, habitat, Chehalis River, Washington

    Freshwater emergent wetlands are common features of large river-floodplain systems. Flood disturbances enhance the productivity of these wetlands, increase wetland water fluctu- ation, and allow riverine fish to access flood-

    plain habitats (Bayley 1991, 1995). Many am-

    phibians use wetlands for mating, oviposition, and larval growth and development (Semlitsch and others 1996). Studies of amphibian use of

    river-floodplain wetlands in the Pacific North-

    west, however, are infrequent. Most of the pub- lished work to date has dealt with amphibian use of inland wetlands and isolated palustrine

    habitats (such as Richter and Azous 1995). These habitats differ from isolated wetlands because river-floodplain wetlands have higher levels of disturbance (water fluctuation) related to riverine flooding, have increased connectiv-

    ity among aquatic habitats, and often contain fish. Water level fluctuations or the presence of exotic fish have been shown to decrease am-

    phibian richness (Richter and Azous 1999; Pearl and others 2005).

    Freshwater wetland restoration projects in

    floodplain environments are designed and

    managed for emergent vegetation, fishes, and waterfowl. Amphibians are rarely a manage- ment focus. Consequently, our goal for this

    study was to describe the amphibian assem- 1 Present Address: Washington Department of Fish and Wildlife, 1182 Spencer Road, Toledo, Washington 98591.


    This content downloaded from on Thu, 12 Jun 2014 23:18:42 PMAll use subject to JSTOR Terms and Conditions


    blages in floodplain wetland habitats of the Chehalis River Valley in southwestern Wash-

    ington. Our specific study objectives were to

    quantify and compare amphibian use across the floodplain at 6 study sites and to determine the effect of wetland restoration on amphibi- ans. Subsequently, we evaluated the potential influence of hydroperiod on amphibian use at the study sites.


    The study was conducted in Grays Harbor

    County in an agricultural floodplain landscape of the Chehalis River. The Chehalis River Basin has a drainage area of approximately 6900 km2 and is the 3rd largest river basin in the State of

    Washington. The study sites were located in the lower Chehalis Basin (below river kilometer 60) where the river is unconstrained and sinuously moves through the floodplain in the broad flat

    valley floor. The basin was chosen for sampling because of its large size and relatively intact and minimally degraded floodplain.

    Six sites were studied: 4 emergent wetlands and 2 oxbow wetlands in the Chehalis River

    floodplain between river kilometer 27 and 60. Two of the 4 emergent wetlands were restored sites with water control structures (R1 and R2), and 2 were reference wetlands (N1 and N2). The reference wetlands were naturally occur-

    ring and had not been impacted by ditching. The oxbow habitat site, 01, was a remnant ox- bow with a beaver dam that contained perma- nent water. The other oxbow habitat site, 02, was a seasonal side-channel wetland off the river's main-channel. All study sites contained fish species (see Henning and others 2006).

    Restored wetlands R1 and R2 contained ren- nie and salzer clays (USDA SCS 1986) and were drained as part of a local drainage district pro- ject to facilitate farming. Wetland enhance- ments in 1997-98 involved blocking drainage ditches by constructing water control struc- tures and levees. The water control structures enhanced wetland hydrology by retaining wa- ter, and levees kept water within the project area to avoid flooding adjacent lands. Water ac- cumulation provided conditions for a diversity of emergent vegetation and reduced nonnative reed canarygrass (Phalaris arundinacea). Winter water depths were similar at the restored sites (1 to 1.5 m). R1 during the summer desiccated to 0.5 ha, but R2 retained about 1 ha of standing

    water. Dense, monotypic stands of invasive reed canarygrass dominated the vegetation at both wetlands before enhancement. After res- toration at R1, native emergent vegetation in- creased and included narrowleaf bur-reed

    (Sparganium angustifolium), swamp smartweed

    (Polygonum hydropiperoides), waterpurslane (Di- diplis diandria), mannagrass (Glyceria sp.), slough sedge (Carex obnupta), and yellow pond- lily (Nuphar lutea). The R2 wetland was drawn down to allow vegetation to germinate during the growing season. Dominant vegetation was reed canarygrass, spotted ladysthumb (Polyg- onum persicaria), narrowleaf bur-reed, marsh cudweed (Gnaphalium uliginosum), slough sedge, and bentgrass (Agrostis sp.).

    The N1 and N2 reference sites lacked water control structures and were chosen based on their proximity and similarity to the restored wetlands, R1 and R2, respectively. The refer- ence wetlands had not been ditched or drained and contained rennie and salzer clays. Re- stored and reference sites connected to com- mon water bodies and exhibited similar hydro- logical patterns and river flows. The wetlands had free-flowing hydrologic connections to the river's mainstem during periods of peak dis-

    charge. However, the reference wetlands did not have surface water outlets, and surface wa- ter disappeared by May at N1 and in July at N2.

    Emergent vegetation colonized the wetlands

    during desiccation. N1 was dominated by reed

    canarygrass. N2 vegetation consisted of reed

    canarygrass, common spikerush (Eleocharis pal- ustris), narrowleaf bur-reed, sedge (Carex sp.), and waterpurslane.

    The oxbow habitats (01 and 02) did not con- tain water control structures or emergent wet- land characteristics. The sites had free-flowing hydrologic connection to the river during most of the sampling season. The 01 study site was a remnant channel with permanent water and connected upstream