GENERAL WETLAND MANAGEMENT TECHNIQUES



GENERAL WETLAND MANAGEMENT TECHNIQUES

FOR MISSOURI

Simply stated, wetland management is a function of raising and lowering water levels in a wetland unit. There are three types of wetlands that are discussed below: a) moist soil, b) emergent, and c) green tree reservoir. All of these exemplify differing plants and are wet during different times and durations in the year. Plants that respond to these water level changes (units that go dry) are commonly referred to as moist soil plants. Smartweed, Millet, Sedge, Beggar-tick, Panic grass, and Cutgrass are all in this group of plants. Moist soil units typically have water present seven to nine months and moist to dry for the remaining portion of the year. The second type of wetland is permanent emergent units. These contain water almost all year and exhibit a totally different vegetative cover. Bulrush, Cattail, Bur-reed, Arrowhead and American Lotus are all considered Emergent type vegetation. “Green-Tree Reservoirs” are a third type of wetland and involve water tolerant tree species. These units are frequently found along major river systems and flood several times throughout the year. Research by the Missouri Department of Conservation has indicated that flooding and de-watering these units under a variety of times and durations over a five-to-seven-year cycle are most productive.

Moist Soil Units:

These units typically involve open lands, ag-units and other low areas subject to flooding periodically from major streams and rivers or mechanical pumping. Drawdown is the term used for removing water from these units. Different timed drawdowns will produce different plant species responses. There are three types of drawdowns: early season; mid-season; and late season. The dates below are approximate because Spring differs from year to year.

a. Early Season Drawdown: N Missouri – mid March to April 1

S Missouri - before May 15 (1)

Vegetation: Smartweeds, Sedges, Millets.

Wildlife use: shorebirds, invertebrates, waterfowl (feeding), some amphibians.

b. Mid-Season Drawdown: N Missouri – April 1 to May 1

S Missouri – May 15 – July 1 (1)

Vegetation: Millets, Sedges, Smartweeds, Beggar-ticks.

Wildlife use: Late migrating waterfowl (feeding), shorebirds, amphibians, rails.

c. Late Season Drawdowns: N Missouri - May 1 to June 15

S Missouri – after July 1 (1)

Vegetation: Cutgrass, Beggar-ticks, Panic grasses, Sedges.

Wildlife use: waterfowl (nesting), amphibians, herons, egrets, small mammals.

A slow drawdown (not more than one inch per day) will accomplish the best results of mixed vegetational response. This usually takes 20 to 24 days or longer to achieve the shallow pool (2-6" of water) and mudflat conditions that moist soil units exhibit. The time of the year that a drawdown is initiated will determine the resulting vegetation. Some wetland managers use the arrival of certain wildlife species as a time to start drawdowns. The arrival of Lessor Yellow-Legs and Pectorial Sandpipers indicate the start of early season drawdowns. For late season drawdowns, use Little Blue Herons and Yellow-crowned Night Herons. When pool conditions allow, disking 1/4 to 1/3 of the pool in scattered patterns will disturb the soil and keep quality moist soil plants growing and prevent invasion of small trees and shrubs. Sometimes undesirable species of plants (cocklebur, asters, and some small trees) appear after drawdown has been complete. Reflooding to the bases of herbaceous plants and overtopping tree seedlings will, at the very least, stunt and weaken the plant, reduce seed production or in many cases kill the plant. Using this technique can be more cost effective than disking and mowing.

Flooding of the units for fall migratory bird use usually occurs in the early to mid fall (N Missouri – early August to early September, S Missouri - Mid August to late September) to provide “water edge” and mudflat conditions mostly for shorebirds. Providing this critical habitat early enough will result in large concentrations of many types of shorebirds which offers tremendous viewing opportunities. Providing water between July 15 and September 1 will provide excellent foraging conditions on invertebrates. This will also provide for early migrating waterfowl like Blue-winged Teal, Green –winged Teal and Pintail.

Emergent Units:

These wetlands usually contain water almost all year long. Cattail, Bulrush, Spikerush, Arrowhead and American Lotus are featured vegetation in these units. Grebes, coots, diving ducks, dabbling ducks, herons, egrets, shorebirds, amphibians, reptiles, invertebrates, as well as game and non-game mammal species utilize those areas sometimes exclusively for nesting, roosting, brood rearing, and feeding. The basic strategy is for partial drawdowns starting mid to late spring (May through July). Keep pools at 40 percent or somewhat lower through the summer to provide water depths of 6-10" of water on the average. The vegetation found in these units are a result of several years of fluctuating water levels, and unlike moist soil units, don’t exhibit dry open ground very often or for very long. Most wetland sites will contain one cell that offers deep-water habitats usually in borrow ditches and natural depressions. After three years of fluctuating water levels and pool depths, emergent-type plants start to prosper. After five or six years, a relatively complete drawdown may be necessary to create some openings in rank emergent pools or rid wood invasions. Some opportunity for fish management exists especially along the major rivers and streams within the State. Timing of the drawdown to accommodate fisheries and waterfowl needs can coincide during the period of time from early August through September. A common problem with emergent pools can be American Lotus or Yanquapin. Over a short period of time it will quickly cover the wetland surface and displace more desirable and beneficial emergent vegetation. Coverage of 40 percent of the wetland water surface is too excessive. Generally, two techniques can be used. A) Hold stable water levels without much fluctuation at 3/4 pool elevations. Research at Mingo National Wildlife Refuge in Southeastern Missouri show dwindling populations after three years of stable, non-fluctuation water levels. This technique, however, over the short term, may decrease plant diversity and some bird usage. After three years, American Lotus dominance should be much reduced. If holding 3/4 is undesirable or not possible, then mowing stands of American Lotus when it starts to flower in late July through early August is another effective technique in control. Avoid disking American Lotus areas as seeds stay viable for 150-200 years. Disking serves only to propagate this plant further. Over a five-year period, American Lotus stands seem to weaken and decrease with this mowing technique.

Green Tree Reservoir:

These units are forested wetlands usually found within levee units and flooded when trees are dormant. This can be a tremendous additional resource for migratory waterfowl, especially in late fall. Green Tree Reservoirs (GTR) are very complex and sometimes difficult to manage (2). Flooding of these units depends on tree dormancy, in part, and regeneration of small seedlings to perpetuate the stand of timber. Initially, flooding a stand of timber has several short-term benefits and several long-term problems. There is increased hard mast production (acorn) and tree growth over the first 4-5 year period. In the long term, continual flooding over time during similar periods and durations caused significant declines in these areas and in some cases killed the timber component completely. An immediate response by waterfowl use is very apparent in the short term but after 10 years, bird use declines markedly.

In short, flooding and de-watering of these bottomland hardwoods over time by natural means has dictated what is present now. Artificial flooding will impact tree survivability as well as regeneration and over time change the timber component of the unit. To duplicate natural flooding that has occurred in the past is the objective in water level management of GTR. Research at Ted Shanks Conservation Area in northeast Missouri has revealed the following about GTR:

- Flood regimes need fluctuations over a 4 -7 year period.

- Flood units starting late August to early September.

- Drawdowns of units completed from late February to early April.

- One year in 4 -7 years, unit was held dry.

In general, fluctuate your flooding and drawdown dates. Units should be flooded slowly with maximum water levels obtained either during waterfowl season or in early spring. One year, full pool should not be obtained and only 3/4 to 2/3 pool depths is the objective. Another year, the unit should be kept dry. In short, flood regimes should be fluctuated in the time span, depth and duration, much like the river would flood the unit over a four-to-seven-year period.

Wetland Designs:

Anything constructed in bottomland scenarios is at risk for floods. Levees should be designed to be “flood tolerant”. Levees that are low and broad (6:1 or 8:1 side slopes) should be favored over ones built taller and steeper (3:1 side slopes). Undulating or crooked more natural appearing levees should be favored over strait “lagoon appearing” levees. The added water edge along the broad-based levees is more attractive to all forms of wetland wildlife. Borrow areas should be located at least 30 feet from the inside toe of the pool or located in the upper reaches of the pool to increase the overall size of the wetland. More recently, borrows created within the pool in a meandering or “serpentine” design associated with higher habitat mounds offer the “macro-topography” requirements (shallow sloughs and mounded areas of relief) for a wide variety of wetland associated wildlife. Sloughs provide a more permanent water source and the mounds provide nesting and loafing areas. Water control structures should be protected with inlet “trash racks” and outlet animal guards to prevent burrowing animals from gaining access and prevent debris from causing drain/fill problems. In northern Missouri, water control structures should be of an “in-line” type located within the levee on the pool side. This will prevent damage from freezing pool water or ice as well as silence “de-watering” noises that attract beaver and muskrat “damming” activities. Vegetation of levees should be flood tolerant such as varieties of Switchgrass (Blackwell variety) mixed with Redtop and Alsike clover. More recently, Switchgrass and Virginia Rye have been planted with a nurse crop of Smooth Brome and Birdsfoot Treefoil with excellent long lasting and flood-tolerant results.

Any trees that need removed during the construction could be anchored inside the wetland at differing elevations to provide “basking logs” for many reptiles and amphibians and should be considered. Care should be taken, however, during the times when Indiana Bats may be nesting or bring off broods. This is usually during the dates 1 April and 1 October of the year. These bats are currently listed as “endangered” per federal and state status lists. They utilize riparian corridors associated with creeks, rivers and their tributaries for feeding and nesting. Nesting is preferred under the loose bark of dead oaks and hickories (especially Shagbark and Shellbark Hickories).

Kevin Dacey

Wetland Wildlife Biologist

Columbia, MO

1) Fredrickson, L. H., and T. S. Taylor. 1982. Management of seasonally flooded impoundments for wildlife. U.S. Fish Wildl. Serv., Resour. Pub. 148. 29 pp.

2) Fredrickson, L. H., and D. L. Batema. 1988. Greentree reservoir management handbook. Gaylord Mem. Lab., Wetl. Man. Series. No.1. 88 pp.

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