The Central Valley of California has provided habitats for some of the largestconcentrations of migratory and wintering waterfowl in North America. Over thelast century, massive destruction of wetlands has occurred, such that less than5% of the original wetland acreage currently exists. One of the impacts ofsuch a broadscale perturbation on the Valley's hydrology is that remainingwetlands on public and private lands are dominated by intensively managedsystems. These systems are typically composed of impounded, historic, wetlandareas, with water delivery systems and independent flooding and dewateringcapabilities. The purpose of this bulletin is to provide a broad overview ofseasonally flooded wetland management in California's Central Valley.
The Central Valley is composed of the Sacramento Valley to the north, SanJoaquin and Tulare basins to the south, and the large Delta area at theconfluence of the major river systems. Climate is dominated by hot, drysummers and cool, wet winters. Rainfall occurs mainly between November andFebruary. The general understanding of rainfall and flooding patterns isimportant if replication of seasonal flooding patterns is to be accomplished inmanaged systems. Rainfall pattern differences do exist across the Valley, withmore seasonal and total rainfall occurring in the Sacramento Valley (Fig. 1).This winter rainfall pattern and peak river discharge from snow melt in Marchsuggest that initial flooding of natural wetlands occurred from October toDecember, with peak flooding occurring in late winter to early spring.Managers have used this information in the manipulation of artificialhydrologic regimes in seasonal wetlands.
Click here for Figure 1.
The term "moist-soil" plant was first described along the Illinois River by JesLow and Frank Bellrose. They used this term to describe plants that germinatedfrom the moist soil or mud as the river water receded from the floodplain.Developing the technique with artificial drawdown and flooding, severalmanagers began to experiment with moist-soil management in this century.Monitoring and research of plant and animal response to these managementpractices has been conducted over the last 20 years, principally by LeighFredrickson and his students in the Midwest. Active wetland management beganas early as the 1880s in the San Joaquin Grasslands, when Miller and Luxirrigated large tracts of grasslands for cattle. These irrigations encouragedabundant moist-soil plants that were exploited as habitat by migratory andwintering geese and ducks. Over the last 20 years, federal, state, and privatewetland managers have demonstrated a desire to provide high quality seasonalwetlands for waterfowl habitat.
The management of productive seasonal wetlands requires dynamic watermanagement, the ability to identify dominant plant species, and anunderstanding of the habitat needs of waterfowl. Managed seasonal wetlands aretypically impounded, historic wetlands that have a water delivery and drainagesystem. Many systems in California are very simple in design, with water inputon the high elevation of a field through a stop-log box culvert. Water inthese simple systems flows by gravity to the low end of the field, where it canbe impounded or drained. Far more complex systems include a mosaic of seasonalwetlands with multiple header ditches for water delivery or drainage, multiplewater control structures on individual wetlands, and pumps to allow movement ofwater during any season (Fig. 2). Functional components of the infrastructuremean the difference between successful management or a degraded sump.
Click here for Figure 2.
One of the principal goals in the management of seasonally flooded wetlands isto provide a myriad of seeds, tubers, browse, and invertebrates for winteringwaterfowl. Although waste grains (e.g., rice, corn, wheat) provide importantcarbohydrates to waterfowl, these foods lack many of the essential proteins,vitamins, and minerals necessary for waterfowl to complete important annualcycle events, such as molt, for subsequent reproductive success the nextspring. By providing a seasonal water regime that encourages moist-soil plantsto germinate and mature, nutritional needs of waterfowl can be achieved.
The types of plants that germinate are determined by several factors andinclude hydrologic regime, seed bank, basin topography, and soil temperature.Most important of these factors, over which a manager has any control, is thehydrologic regime. This water cycle is determined by when the water comes off,irrigations, when the basin is flooded, how deep the basin is flooded, and howlong the basin is flooded. The general pattern of flooding seasonal wetlandsincludes draining the basin between March and June, from one to fourirrigations, and flooding the basin between September and December. Themajority of intensively managed wetlands are flooded by late October or earlyNovember to coincide with an increasing arrival of waterfowl migrants.Sequential flooding (see Valley Habitats, Number 3) of seasonal basins(September to December) within a wetland complex, results in greater overallbird use of an area and reduced loss of seeds and tubers throughdecomposition.
Managed seasonal wetlands in California yield robust, perennial emergentvegetation and annual-dominated, moist-soil plants. Tule bulrush and cattailtend to dominate the emergent growth, while important moist-soil plants forwaterfowl include ammania, fathen, brass buttons, burhead, chufa, watergrass(or barnyard grass), swamp timothy, smartweed, sprangletop, and beggerticks.Plants which may form monocultures and are considered less desirable forwildlife values include knotweed, cocklebur, river bulrush, baltic rush,Johnson grass, common reed, and salt grass (see Valley Habitats, Number 7).
The timing of water drawdown is critical in determining the plant composition,since germination of wetland plants is triggered by soil moisture andtemperature. Drawdown of a Sacramento Valley wetland in March may be dominatedby smartweed, tule bulrush, and spikerush. Drawdown in late April may bedominated by swamp timothy, pricklegrass, fathen, and dock. Drawdown in Maymay be dominated by watergrass, sprangletop, ammania, and cocklebur. Timing ofdrawdowns in the San Joaquin Valley can be 2-4 weeks earlier than for wetlandsin the Sacramento Valley but produce fairly similar plant composition.
Slow (2-3 weeks) drawdowns concentrate invertebrate prey that may be exploitedby migrant or breeding waterbirds. More rapid drawdowns (2-7 days) may be moreappropriate where salinity is a problem. Rapid drawdowns can flushconcentrated salts from the soil surface but it is advisable to reflush thebasin with fresh irrigation water if possible. Rapid drawdowns tend to resultin large bands of monocultures or relatively few plant species, because allsoils are exposed to the same temperature at the same time. Managers ofseasonal wetlands in former tidal lands (Suisun Marsh or San Pablo Bay) shouldconsult specific references, such as Rollins, 1981, to avoid problems withsalinization and soil acidification.
Irrigations of moist-soil plants are important so these plants can reach seedmaturation and outcompete more "dry-land" weeds. Irrigations may occurnaturally through spring (April-June) rains or artificially through surfaceirrigation. Wetlands dominated by smartweed, watergrass, and sprangletop cansurvive with a single irrigation 4-8 weeks after germination, but plantstructure and seed production is generally for more lush with 2-4 irrigations.Swamp timothy, tule bulrush, and fathen can produce lush growth with a singleirrigation, especially if very fresh water is used. A final irrigation inearly fall can produce a new generation of stunted, moist-soil plants andcomplete seed maturation of any water stressed plants.
The hydrologic regime is composed of the timing, duration, and depth ofseasonal flooding. To mimic rainfall patterns, fall and winter flooding cancoincide with seasonal rains or pumped surface water. Some minor flooding maybegin by late August for migrant northern pintails, but other basins may bedelayed for flooding until late November or December, so that newly floodedhabitat is available. Delaying such flooding may save money on pumping costsif it is a wet year. Seasonal basins should remain flooded until at leastFebruary (although March-June is recommended) to begin the dewatering andgermination process again. It is also important to provide wintering andspring staging habitat for waterfowl after hunting seasons have ended. Gradualfloodup is recommended to allow waterfowl maximum accessibility to seeds,tubers, browse, and invertebrates. To provide optimal microhabitat and accessto forage, water depths from 0-18 inches are recommended, with sequentialmicrohabitat available at 2-6 inches depth.
To maintain productive seasonally flooded wetlands, the hydrologic regime mustbe dynamic. Consider altering drawdown and flooding dates for individualbasins from year to year. This option is most available to areas with acomplex of managed basins.
An excellent introduction to the concepts of moist-soil management is availablein Fredrickson and Taylor, 1982. Federal, state, and private sector biologistscan suggest alternatives in management and seeking their advice is encouraged,but the best teacher is personal experience. Short-term "mistakes" are onlyfailures if they are repeated or result in long-term degradation of the wetland(e.g., pothole blasting or stable water regime).
Euliss, N.H. Jr. and G. Grodhaus. 1987. Management of midges and otherinvertebrates for waterfowl wintering in California. Calif. Fish and Game73:242-247.
Fredrickson, L.H. and F.A. Reid. 1986. Wetland and riparian habitats: Anongame management overview. Pages 59-96 in J.B. Hale, L.B. Best, and R.L.Clawson, ed. Management of nongame wildlife in the Midwest: A developing art.N. Cent. Sect. Wildl. Soc., Chelsea, MI.
Fredrickson, L.H. and F.A. Reid. 1990. Impacts of hydrologic alteration onmanagement of freshwater wetlands. Pages 71-90 in J.W. Sweeney, ed.Management of dynamic ecosystems. N. Cent. Sect. Wildl. Soc., West Lafayette,IN.
Fredrickson, L.H. and T.S. Taylor. 1982. Management of seasonally floodedimpoundments for wildlife. U.S. Dep. Inter., Fish and Wildl. Serv. Resour.Publ. 148, Washington, DC. 29pp.
Heitmeyer, M.E., D.P. Connelly and R.L. Pederson. 1989. The Central,Imperial, and Coachella Valleys of California. Pages 475-505 in L.M. Smith,R.L. Pederson, and R.M. Kaminski, eds. Habitat management for migrating andwintering waterfowl in North America. Texas Tech. Univ. Press, Lubbock.
Reid, F.A. 1985. Wetland invertebrates in relation to hydrology and waterchemistry. Pages 72-79 in M.D. Knighton, ed. Water impoundments for wildlife:a habitat management workshop. U.S. For. Serv., St. Paul.
Reid, F.A. 1993. Managing wetlands for waterbirds. Trans. N. Am. Wildl. andNatur. Resour. Conf. 58:345-350.
Rollins, G.L. 1981. A guide to waterfowl habitat management in Suisun Marsh.Calif. Dep. Fish and Game Publ. Sacramento. 109pp.
Smith, W.D., G.L. Rollins and M.R. McLandress. 1994. A guide to wetlandhabitat management in the Central Valley. Mimeo, Sacramento. 34pp.
Prepared by: Frederic A. Reid, Regional Biologist, Ducks Unlimited, Inc.,Sacramento, California.
Valley Habitats is published as part of Ducks Unlimited's VALLEY CARE Programto provide information to private land managers who wish to integrate wildlifemanagement into their existing operations.
For more information regarding conservation related land management practicescontact: Ducks Unlimited, Western Regional Office, 9823 Old Winery Place, #16Sacramento, CA 95827
TELEPHONE: (916) 363-8257 FAX: (916) 363-9849
Valley Habitats is produced by Ducks Unlimited's Western Regional Office.Items contained herein may be reproduced with permission. Copyright, DucksUnlimited, Inc., 1995.
The National Fish and Wildlife Foundation, Hofmann Foundation, and WildlifeConservation Board provided the generous funding for this issue of ValleyHabitats.