Before reviewing examples of habitat management methods to remedy commonwetland vegetation problems, it is important to gain a perspective of thereasons for the problems. The germination and growth of different plantspecies and quantities of vegetation result primarily from the timing, depth,and duration of water application. Other variables such as soil type and airtemperature contribute, but none quite as much as those related to water.Prior to manipulation of problem vegetation, it is important to identify thecause and effect, or "conditions" responsible for vegetation problems. Untilthe conditions under which problem vegetation proliferated can be modified,there is little chance of affecting a long-term solution to the problem. Inother words, a manager may expend large amounts of time and dollars impactingthe symptom rather than the source of the problem.
Having recognized potential relationships between water regime and vegetationcomposition, the next step is to select the appropriate corrective measure.Treatments can vary and include: changing the drawdown, irrigation, or floodupschedule; burning; physical manipulation with heavy equipment (e.g., mowing,discing, excavation); or even chemical control. Each treatment has inherentadvantages and disadvantages. For example, when considering changes to thewater regime, results may not occur as quickly as desired. Total control ofwater also may not be possible and timing of critical irrigation water maydictate dominant vegetation. When considering mowing or burning to decreasethe amount of standing vegetation, it is little more than a "cosmetic" controland will probably be required on a regular basis. If discing is used insteadof mowing or burning, the results may last longer, but current waterfowl foodproduction may be sacrificed or a hunter's access across the pond bottom maybecome difficult. Excavation modifies conditions the most and thereby producesthe longest term results; however, it is expensive, requires specializedequipment, and may degrade rather than improve a site. Chemical applicationsalso can be expensive, time consuming, risky to desirable plant species, andusually are used only as a last resort. Often a combination of several ofthese techniques will produce the best and longest lasting results in a wetlandcomplex.
Habitat management options are discussed for the control of five problemvegetation types: cattail/bulrush, knotgrass, common cocklebur, Johnson grass,and common reed.
Most often referred to as tules, heavy emergent wetland cover in California'smarshes is comprised of either cattails (Typha spp.) or hardstem bulrush(Scirpus acutus). Both plants are tall (5-10 feet) emergents and can reproducevegetatively, growing new plants from rhizomes (roots). However, cattailsoften invade a wetland much faster than bulrushes and are able to "take-over"large expanses in a single growing season because of their mass quantities ofwind-borne seeds. Cattails also are more water dependent during the growingseason than bulrushes. The vigor of an established stand of cattails can bereduced dramatically by lack of water for long periods (a whole growing seasonor more). In contrast, hardstem bulrushes are much slower in establishing andspreading because they proliferate primarily through underground rhizomesrather than seeds. Bulrushes also are much better equipped to withstand long,dry periods and, therefore, can be more difficult to eradicate than cattails.Some dense emergent cover is certainly beneficial on your area to shieldwaterfowl from heavy winds and resulting wave action. In addition, a host ofother bird species use this cover for roosting or nesting during certain timesof the year. However, if too widespread or dense, tules can reduce thediversity and productivity of a marsh and result in decreased waterfowl use.The goal is to maintain a desirable mixture of open water, emergent plants forcover, and other plants for food. Marsh management that creates a mosaicpattern of 50:50 plant to water interspersion provides the highest qualityhabitat for dabbling ducks. However, a 30:70 or 70:30 mix may provide goodquality habitat for certain waterbird species on a specific wetland.
Here is an outline of the steps necessary to control overgrown tule areas by acombination of discing and burning:
1. Draw down the overgrown pond in March to decrease spring green-up of tallemergents.
2. Keep the pond dry through June.
3. Begin the project in late June, or whenever the pond bottom will support atractor and heavy stubble disc. Open the disc only slightly and "roll-down"the areas of tules you want to remove. Strive to create a mosaic pattern (Fig.1) by leaving vegetation in a patchwork of varying sizes. A second pass may berequired to sufficiently knockdown the standing cover (Fig. 2).
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Figure 1.
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4. Allow treated vegetation to dry for 7-10 days.
5. A number of factors should be considered before the burn is conducted. Youmust: establish a safe perimeter (fireline); take special precautions toensure the safety of trees and cover around blind sites; and obtain permissionthrough your local county agricultural office and fire department. Burn thearea by igniting "rolled-down" sections only (Figs. 3 and 4).
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6. After the burn is completed, use a tractor with a fully opened disc to turnup the root zone (roots and rhizomes) in all previously disced areas. Wherepossible, cross-disc the site.
7. Allow as much time as possible (at least two months) to "bake" exposedroots in the intense summer heat.
8. If feasible, redisc in late August.
9. Do not floodup until October.
A few notes about this procedure:
a. If the existing vegetation is not too dense, burning to remove residualcover may not be necessary. However, for the disc to be effective, it must beable to cleanly contact and turn the ground. Without burning, most old tuleclumps are too thick to allow the disc to cut. If too thick, very little ofthe root zone will be affected, and the plants will quickly reestablishthemselves.
b. Do not be too concerned if the entire area burns. Unless you also alterthe root or rhizome zone (4-8 inches), most emergent vegetation will eventuallyreestablish itself once water is applied. By following earlier tractor anddisc tracks applied during Step 6, a marsh mosaic is assured.
If done properly and thoroughly, these treatments should produce results whichlast for a minimum of (3-5) years. Future water control and habitat managementwill play a critical role in guaranteeing long- term effectiveness (Figs. 5 and6).
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Click here for Figure 6.
Also known as jointgrass or ditchgrass, knotgrass (Paspalum distichum) is aperennial that resembles a rather robust bermuda grass commonly found inresidential lawns. It can often become a problem in wetland units managed formoist soil species such as smartweed (Polygonum spp.) or barnyardgrass(Echinochloa crusgalli). Because moist-soil wetlands are often irrigated tobring the food "crops" to maturity, knotgrass benefits from the moistconditions and can invade large acreages by spreading rhizomes. To combat thisproblem, use a combination approach of: extended drying, mowing, burning, andthen reflooding immediately. Specifically:
1. The affected wetland unit is drawn down under a normal regime, usually theend of April.
2. No irrigation is applied during the summer, this extended drying stressesthe knotgrass as much as possible.
3. Floodup is delayed until September.
4. Prior to floodup, the thickest areas of knotgrass are mowed using largetractors pulling rotary mowers. This improves conditions for a more completeburn by drying and exposing much of the vegetation as deeply into the "clump"of the plant as possible.
5. Once the fireline is established around the perimeter, the burn iscompleted.
6. The entire wetland should then be reflooded as quickly as possible. Idealdepth would be 1 foot or more above ground level.
This combination treatment effectively stresses the plant and expends it'senergy reserves; burns and removes existing stressed vegetation while "baking"the root zone; and starves the remaining plants for oxygen, thus hamperingregrowth. Upon flooding, some of the watergrass and smartweed that germinatedon the drawdown will grow to maturity. The wetland is flooded throughout thewintering period and drawn down late April through mid-May of the followingspring. At this time, seeds produced during the previous September and thosepresent in the soil's seed bank, will germinate and grow with the benefit ofreduced competition. In this way, excellent stands of moist-soil plants can bereestablished in units formerly dominated by knotgrass.
This coarse, annual plant may be quickly recognized by hunters, as it producesa seed or bur that often becomes entangled in their dog's fur. Howeverinconvenient, this may be the least of the problems this plant produces! Oflittle wildlife value, common cocklebur (Xanthuim strumarium) is tall andbroad-leafed, thereby outcompeting or shading out more desirable plant species.It germinates at a wide range of temperatures and can invade large acreages ofwetlands. Cocklebur germination is encouraged by rapid drawdowns that dry andwarm the soil quickly. This is especially true in recently disturbed soilsand, as a result, some treatment techniques such as discing, only make thisplant problem worse.
Similar to the other examples, a number of management options exist: flooding,mowing, and a combination of both is ultimately the best. After cocklebur hasgerminated, if young plants (2-6 inches in height) are covered with water(flooded) for 6-14 days, then a large percentage of the plants will be killed.The number of days required for flooding will depend on the dailytemperature--the hotter the better! Warmer temperatures can have shorterdurations than cooler temperatures. This technique is often referred to as"scalding" and prohibits oxygen intake and gaseous exchange between leaves androots. At the same time, the flooding benefits other more desirable wetlandspecies that may have germinated in the same wetland, such as smartweed,barnyardgrass, and sprangletop (Leptochloa fascicularis). This increasescompetition from desirable plants, further decreasing cocklebur's chances.
Another technique is mowing. If plants can be mowed as close to the ground aspossible after maximum stem growth but prior to flowering, a significantpercentage of the plants will not regrow and those that do will be smaller andproduce less seed. Because cocklebur growth is apical (grows from the tip),"knocking the top off" of the vegetation will stop growth. The new germinationcan again be mowed prior to flowering to increase the impact.
The best results involve the combination of these two techniques:
1. Allow the plants to reach maximum stem height prior to flowering.
2. Mow the problem area as close to the ground as possible.
3. Immediately flood to a depth of 6-12 inches (covering the plants) for 10-14days.
Again, duration of flooding to achieve desired results will depend ontemperature--the hotter the better.
Keep in mind that established cocklebur stands have tremendous "seed banks"which have long viability and do not all germinate at the same time. As aresult, treatments may need to be repeated throughout the growing season or fora number of years to all but eliminate this problem plant.
This grass species (Sorghum halepense) is a common weed throughout disturbedsoils of the Central Valley. It is most problematic in the peat soils of theSacramento-San Joaquin Delta. Germination can occur after drawdowns ofseasonal wetlands, especially on hammocks or ridges such as field borders orlevees. Once established, it can quickly result in a monoculture. This plantwill remain a problem if irrigation of the site is not possible. However,control of Johnson grass is fairly simple through water or minor chemicalcontrol. Where Johnson grass makes up a dominant portion of germinated plants,irrigation (6-14 days) should occur either early (June-July) or late(August-September) to "scald" the plant. This irrigation will improve survivaland growth of more desirable moist-soil plants. Glyphosate (e.g., rodeo) is anherbicide that has proven to be very effective on Johnson grass, but may becost prohibitive to spray an entire field and would impact other grasses. Spotspraying may be possible where only patches of the plant currently exist.
The perennial grass, common reed (Phragmites australis), is widely distributedthroughout lower elevations in California, but problems of monotypic stands areexperienced most in the Suisun Marsh and Delta. This plant occurs infreshwater or brackish marshes. More saline waters may be less favorable tocommon freshwater moist-soil plants and periods of brackish inundation infreshwater marshes have encouraged the invasion of phragmites in several areasof the Suisun Marsh. This plant usually becomes established on dry or moistborders of a wetland, but can quickly become established in shallow waterareas. It spreads vegetatively through creeping rhizomes, while shoot growthoccurs from March to June. Large monocultures of phragmites are most usuallyassociated with impounded areas and stabilized water regimes. This plantbecomes less competitive with other moist-soil plants when variation in thetiming of floodup and drawdown is included in the flooding schedule.
Several techniques, including physical, burning, and chemical control, haveproven effective in reducing phragmites stand vigor. However, none of themethods are totally effective across all growing conditions of this plant.Multiple treatments will most likely be necessary to reduce established stands.Physical disturbance using discs, rototillers, rollers, and mowers has proveneffective on drained sites. Burning can provide easy access for discing.Manipulations are most effective if conducted in late summer or early fall,when cut rhizome survival is reduced. Spring manipulations may actuallystimulate dense growth. Where large, dense stands are present, strip discingmay improve interspersion of open water and plants but, phragmites will expandunless multiple-year efforts are conducted. Cross-discing in late summer is aneffective means of reducing stand vigor. Burning in late summer may beeffective in retarding expansion of a stand, but if performed in spring, thiswill stimulate bud growth. Systemic herbicide (e.g., amitrole, dalapon, andglyphosate) application is most effective when reserves are being shunted tothe rhizomes (late summer or early fall). Control of phragmites is oftenachieved by combining these treatments over several years. For example, afterextensive discing, new fall shoots of the plant may be spot sprayed with asystemic herbicide. Once phragmites is established as a dense monoculture,multiple treatments over several years may be necessary. Thus, areas wherephragmites is just becoming established allow for the greatest control withminimal expense.
Regardless of the problem species or treatment applied, a few furtherconsiderations are worthwhile. First, water availability and control areessential for certain treatment methods. If they are not adequate, you may bewasting a lot of effort or even make a bad situation worse! Second, accurateassessment of the magnitude or extent of the vegetation problem as it relatesto the entire pond or wetland is important. If the troublesome vegetationexists on only a small percentage of the total wetland, it may not be worthtrying to remove it if risking harm to the remaining (majority) plantcommunity. Small stands of these less desirable species can contribute to theoverall diversity of the area. Third, we must also recognize the importance ofgeographic location. Management techniques developed in one part of the stateand discussed here may not produce the same result elsewhere. They may requiremodifications in timing and methodology for your specific area.
There are a number of publications, agencies, and organizations capable ofproviding advice on controlling problem vegetation. Because there is nosubstitute for experience, it is in the land manager's best interest to reviewthe greatest number of possible options.
Cross, D.H. and K.L. Fleming. 1989. Control of Phragmites or common reed.U.S. Fish and Wildlife Leaflet 13.4.12.
Fredrickson, L.H. and F.A. Reid. 1988. Preliminary considerations formanipulating vegetation. U.S. Fish and Wildlife Leaflet 13.4.9.
Fredrickson, L.H. and F.A. Reid. 1990. Impacts of hydrologic alteration onmanagement of freshwater wetlands. Pages 71-90 in J.M. Sweeney, ed.Management of dynamic ecosystems. North Central Section, The Wildlife Society,West Lafayette, Indiana.
Fredrickson, L.H. and T.S. Taylor. 1992. Management of seasonally floodedimpoundments for wildlife, U.S. Dep. Int., Fish and Wildlife Service Resour.Publ. 148, Washington D.C., 24pp.
Heitmeyer, M.E. D.P. Connelly and R.L. Pederson. 1989. The Central, Imperial,and Coachella Valleys of California. Pages 475-505 in Smith, L.M., R.L.Pederson and R.M. Kaminski, ed. Habitat management for migrating and winteringwaterfowl in North American, Texas Tech Press, Lubbock.
Sojda, R.S. and K.L. Solberg. 1993. Management and control of cattails. U.S.Fish and Wildlife Leaflet 13.4.13.
Strong, M.A., J.G. Mensik, and D.S. Walsworth. 1990. Converting rice fieldsto natural wetlands in the Sacramento Valley of California. Trans. West. Sect.Wildl. Soc. 26:29-35.
Prepared by: J. Greg Mensik, Supervisory Wildlife Biologist, U.S. Fish andWildlife Service Sacramento National Wildlife Refuge Complex, Willows,California and Frederic A. Reid, Regional Biological Supervisor, DucksUnlimited, Inc., Sacramento, California. Plant illustrations from HerbertMason, A Flora of the Marshes of California. Copyright (C) 1957 Regents of theUniversity of California, (C) renewed 1985.
The National Fish and Wildlife Foundation, Hofmann Foundation and WildlifeConservation Board provided the generous funding for this issue of ValleyHabitats.
Valley Habitats is produced by Ducks Unlimited's Western Regional Office.Items contained herein may be reproduced with permission. Copyright, DucksUnlimited, Inc., 1995.
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