The diversity of wildlife species in Missouri's freshwater marshes is unmatched by any other type of habitat in the state. Management of these marshes can be challenging and rewarding. Management techniques used in a particular wetland depend on one's objectives and the amount of water control that is available. If water control is possible, you can provide a great deal of habitat through water manipulations. If water control is not possible certain practices can still improve the wetland to meet your desired objective. Listed here are some important management techniques that can be used to enhance wetland habitat.
|Wetland Habitat Types||Water Control Needed||Draw-Down Dates||Dates of Re-flood||Typical Important Native Plants||Typical Food Plants That Can be Planted|
Flood while dormant only
|Drain 100% and vary re-flooding depths annually||January 1 to March 15 vary annually||October 15 to December 1 vary annually||Pin oak; pecan;willow oak, overcup oak, cherrybark oak, ragweed; smartweeds, spanish needles||Japanese millet, pin oak and pecan seedlings, maples, cottonwoods, bottomland timber with understory shrubs|
|Seasonally Flooded Croplands||Drain 100% and re-flood||In time for spring farming||Start by October 15 or after crop harvest||Pigweed, ragweed, wild millet, foxtail, smartweeds, panic grass, crab grasses, rice grasses, Spanish needles, buckwheat||Corn, grain sorghum, Japanese millet|
Maximum Diversity of Wildlife and Wetland Communities
|Mud flats: up to 100% drawdown
Emergent Marsh: 50% drawdown of total area
|May 1 to July 1||September 1 through November 15||Mud Flats: Wild Millets; yellow nutgrass, smartweeds, rice cutgrass, button bush
Emergents: Arrowhead, smartweeds, willows, bulrush, lotus, cattails
Submergents: Coontail pondweeds
|Japanese millet, transplant native marsh plants|
|Small Lakes and Farm Ponds
Narrow band, edge management
|Lower water to expose edge as practical||Early June||Fall rains to refill||Cattails, willows, lotus, sedges, pondweeds, shrubs, bulrushes, smartweeds, wild millet||Japanese millet, transplant native marsh plants|
Shorelines of city reservoirs, larger lakes, strip pits, river banks
|No water control||Willows, maples, cottonwoods, bottomland timber with understory shrubs||Millets (mud flats), upland grain food plots|
|Wetland Habitat Types||Animal Life Most Benefited||Some Added Benefits|
Flood while dormant only
|Mallard, beaver, wood duck, woodcock, mink, squirrel, raccoon, herons||Substantial waterfowl and raccoon hunting, furbearer harvest, birdwatching, nut harvest, timber harvest|
|Seasonally Flooded Croplands||
Migrant waterfowl, songbirds, shorebirds, jack snipe, rails
|Substantial waterfowl hunting, snipe hunting, rail hunting, control of crop pests and weeds|
Maximum Diversity of Wildlife and Wetland Communities
|Marsh songbirds, frogs, turtles, raccoon, muskrats, waterfowl, mink, herons, egrets, fish, aquatic insects, shorebirds||Furbearer harvest, moderate waterfowl hunting, moderate fishing, cattle water.|
|Small Lakes and Farm Ponds
Narrow band, edge management
|Shorebirds, frogs, fish life, muskrats, upland and marsh songbirds, deer, waterfowl||Fishing, waterfowl hunting, furbearer harvest, swimming , cattle water, irrigation, water supply|
Shorelines of city reservoirs, larger lakes, strip pits, river banks
|Beaver, muskrats, waterfowl, shorebirds||Fishing, swimming, waterfowl hunting, picnicking, water supply, water sports|
Moist-Soil Management (Seasonally Flooded Impoundments)
Moist-soil management refers to management of land to provide moist soil conditions during the growing season to promote the natural production of beneficial plants. Seeds produced by these plants often attract and concentrate waterfowl and other wetland wildlife species. The decomposing vegetative parts of moist-soil plants also provide substrata for invertebrates, which are critical food for many wetland wildlife. Factors that determine the success of moist-soil management include: the timing and rate of the de-watering; soil disturbance and the stages of plant succession; and the timing and rate of re-flooding. Best success is achieved when water levels can be controlled, although good results can be obtained under natural conditions when artificial draining and flooding are not possible. The following are techniques used in moist-soil management:
- Hold water on the land until late spring, generally early May through June. This will help prevent some undesirable plants that need dry conditions to germinate and will provide extended habitat for wetland wildlife. Drawdowns (de-watering) early in this time period tend to produce smartweeds, while mid period drawdowns often produce wild millets. Late drawdowns in this time period usually result in beggar-ticks, panic grasses and crab grass.
- Drop water levels at a slow rate--generally about 1 inch a day--until the marsh bottom is exposed. Slow drawdowns prevent soils from drying too quickly and produce desirable plants over an extended period. Slow drawdowns usually produce a greater diversity of plants, while a fast drawdown (de-watering in a few days) produces extensive stands of similar vegetation. Fast drawdowns late in the season tend to dry the soil too quickly and often result in less desirable vegetation. The stage of plant succession in a marsh unit will also affect the plant species composition following a drawdown Perennial plants like rice cutgrass and marsh smartweed tend to increase after three or more years without a soil disturbance (disking). Many of the high seed-producing plants like wild millet and large seeded smartweed occur in units in the first few years following a soil manipulation.
- Start re-flooding the moist-soil unit from early September to mid-October depending on your particular objectives. A slow, continuous flooding of the unit will provide optimum feeding conditions for many wetland species. Flooding depths are critical to successful moist-soil management. Many species of wildlife including most ducks prefer water depths of less than 6 inches and as little as 2 to 3 inches. Flooding marshes too deep is not only costly but often puts food too deep for wildlife to utilize.
The above drawdown procedure should produce a variety of moist-soil plants, including: smartweeds, wild millet, rice cutgrass, beggar-ticks and many others. During long summer dry periods, shallow re-flooding (irrigation) will stimulate moist-soil plants and can even kill or set back undesirable plant species, such as cocklebur and morning glory. Moist-soil plants are not adversely affected by summer flooding, as long as one-third of the growing plant is out of the water.
Some moist-soil plants can become too dense or reach heights which make them unavailable to many wildlife species. Midsummer mowing to a height of 18 inches will make these areas more attractive. Mowing native plants that have already produced viable seed is no longer considered baiting for waterfowl.
Most desirable moist-soil plants occur in early stages of plant succession in a marsh community. Seed production for these plants is also usually highest in the early stages. Although units vary, most marshes should be disked once every three to five years to set back plant succession. This disking will also help control woody plant invasion and can be used to control undesirable plants like cocklebur. When possible disking should be rotated over a unit so that all parts have been disked in a three- to five-year period. A late summer disking followed by a shallow flooding is especially attractive to shorebirds and early migrant waterfowl. Invading woody plants and other undesirables can also be temporarily controlled by mowing. Mowing is especially effective when desirable moist-soil plants occur under rank cocklebur. The mowing will remove shade and competition, and moist-soil plants will begin growing rapidly, especially if irrigated. Remember that mowing is usually only a temporary cure, as most woody plants will re-sprout after being mowed. Disking the ground is a better practice, because it will help remove woody plants and encourage moist-soil plant production.
Seasonally Flooded Croplands
Cultivated crops, especially corn and milo, can provide an important component in wetland management They provide an excellent source of carbohydrates, often replacing the energy needs for wildlife historically provided by acorns in flooded bottomland forests. They also serve as an important tool in moist-soil management. The soil disturbance associated with planting row crops, when rotated through a marsh, helps keep the unit in an early successional stage, thus encouraging moist-soil plants. Naturally occurring weeds in cultivated crops, such as ragweed, foxtail, millets and smartweeds, add additional food sources for many wetland wildlife species.
Water management for cultivated crops should be similar to moist-soil units, although slightly earlier drawdowns and later re-flooding may be necessary. Japanese millet that is obtained commercially is often used in mud flats or disked areas to supplement natural foods. It should be planted at two week intervals from late June through July at rates from 10 to 15 pounds an acre. Japanese millet often takes a rain or irrigation to stimulate germination. Mowing Japanese millet back to a height of 12 inches when the first seed head is seen often increases seed production, while making the plants less attractive to blackbirds and more available to other wetland wildlife.
Managing Wetlands: Greentree Reservoirs (Flooded Live Timber)
The availability of flooded bottomland hardwood timber from late fall to early spring is critical to the breeding success of the mallard duck. Many other species also depend on this important wetland habitat.
Several million acres of bottomland hardwood timber once occurred in Missouri and throughout the lower Mississippi River valley. Today only a fraction of this unique wetland habitat remains. Recent studies have shown that the availability of flooded bottomland hardwood timber from late fall through early spring is critical to the breeding success of the mallard duck. Other studies have shown that many other species of wildlife also depend on this important wetland habitat.
- Historically, greentree reservoirs (leveed bottomland timber that is artificially flooded) were developed to attract waterfowl during the fall and winter hunting season. Studies have shown that flooding these units the same time and depths year after year resulted in a reduction in acorn production and tree vigor, as well as causing timber mortality. Today, managers realize that long-term productivity and survival of the forest should be their management priority. To ensure that greentree reservoir habitat is available for generations to come, owners and managers should implement the following techniques:
- Vary flooding and de-watering dates. Try to emulate natural water regimes. Timber should not be artificially flooded before leaves begin to turn color in the fall, and timber must be drained before new leaves appear in the spring. Vary the dates of flooding in the fall up to a month and de-watering in the spring by up to three months. Vary flooding dates from year to year over a several year period. Flood slowly to provide optimum habitat conditions over an extended time period. Leave the unit unflooded one out of every six to eight years.
- Vary flooding depths. Flood at different depths from year to year and even within the same fall-winter period. Remember the preferred feeding depths of many ducks is less than six inches. Partial drawdowns that produce "puddling" of water tends to concentrate invertebrates that live in the leaf litter and provide an important food source.
- De-water slowly. Nutrients associated with leaf litter decomposition that promote invertebrates and good timber vigor usually peak in early spring. A rapid de-watering of a greentree unit flushes away these nutrients. Always remove water that has been in the unit during the fall and winter slowly (one inch water level per day or less).
- Remove flood waters without delay. Flood water that inundates the wetland unit during the growing season should be removed as quickly as possible. Flooding during the growing season can cause stress and, ultimately, tree mortality if not removed within a few days. Constant monitoring of water control structures is necessary to make sure that flood waters are being drained during the timber's growing season.
- Practice good timber management. Acorn production, regeneration and reforestation all depend on a good forest management plan. Consult your local district forester to help with timber management.
Farm Ponds and Small Lakes
Farm ponds and small lakes generally are not well suited for successful marsh management. When drainage of these areas is possible, a slow 1- to 2-foot drawdown in early June usually will stimulate the growth of beneficial plants on the exposed mud flats. Fall and early winter rains will refill these ponds and lakes, making food and cover available to marsh dwellers until the next drawdown. Establish food and cover strips around the water's edge and sow Japanese millet on mud flats, if production of natural plants is limited. Protecting the shoreline from livestock is essential for ponds to remain valuable to waterfowl.
Although the numbers of natural sloughs and oxbow lakes have dwindled considerably over the last few decades, they still are valuable wetlands in many areas of Missouri. When water control is possible, an owner can use the same drawdown techniques described earlier. When water control is impossible, the following steps will make these areas more attractive to wetland wildlife:
- Establish food and cover strips around the slough and encourage production of native plants.
- Plant strips of corn or milo to attract a variety of wildlife, if the slough is located on open bottom-lands.
- Plant bottom-rooted marsh plants in shallow water areas.
- Plant pin oaks and pecans near the water's edge.
- Control bottom-feeding fish, such as carp and bullheads, to obtain the clear water needed by aquatic insects and plants.
- Sow Japanese millet or smartweed seed at the water's edge when evaporation exposes mud flats.
In some sloughs, overcrowding of aquatic plants is a problem. Plants, such as cattails, bulrushes and lotus, can take over in shallow marshes. When drawdown is possible, this vegetation can be mowed and burned allowing the soil to dry. Once dried, disking will remove undesirable species and stimulate the germination of more desirable moist-soil plants.
When drawdown is not possible there are some alternatives. For example, muskrats can control dense vegetation. The best waterfowl marshes seem to have about equal amounts of plant cover and open water. During the fall, muskrats cut plants for use in lodge construction and for food, creating marsh openings that balance open water and cover. But muskrats need control, too. High muskrat populations can damage levees and strip off too much vegetation, literally eating themselves out of house and home. Control of furbearers is covered elsewhere in this site.
Managing Wetlands: Opportunistic Flooding Management Options
Several landowners have developed shallow water impoundments where a guaranteed water source for re-flooding is not available. Under this circumstance, management practices may vary from those discussed earlier where re-flooding capabilities do exist. The first option to consider is whether to de-water the unit to encourage a vegetative response or to hold the water through the year. One option would be to conduct a drawdown, as discussed in the moist-soil management section, then allow the unit to re-flood opportunistically in late summer through fall or even winter. This water would then be held in the unit throughout the next year or two. Under this management plan, moist-soil plant seeds would be available immediately after initial flooding, then invertebrates would be available until the unit is again de-watered in late spring up to two years later.
Another option is to hold water in a unit from three to five years to encourage emergent or aquatic vegetation. This technique will provide a lower number of plant seeds, but will still provide an important wetland habitat type for many wildlife species. In this option, food sources would be mainly invertebrates associated with a more stabilized water agent system would be de-watered every three to five years to allow plant regeneration and encourage nutrient cycling (release of nutrients from organic matter by decomposition, making nutrients available for plant growth). Once the unit is de-watered, disturbing the soil by disking will encourage moist-soil plants to return. After disking, one of the above management options could again be initiated.
A third option is to manage these units in a moist-soil system. Following an annual spring drawdown, the unit might remain dry in the fall, but would often refill sometime in the winter or spring. Fall habitat would sometimes be available, but newly flooded habitat would be available in late winter or early spring in most years. These newly flooded spring areas are important and increasingly rare habitats for many migrating birds.
Whichever management option you select, remember that water will not necessarily be available when you want it. You should plan ahead and make the most of the water when it does become available.
Controlling Undesirable Species
Undesirable plants are defined as plants that can cause problems in wetlands under certain conditions. These plants in turn can provide beneficial conditions in other circumstances. For example, marsh smartweed, being a perennial, produces very little seed and can crowd out other more beneficial plants, but it provides an excellent environment for invertebrates, another important food source for many wetland wildlife species. In some cases, plants are listed as undesirable because they are very aggressive and will crowd out other plants, resulting in a monotypic stand, which is less desirable than a mixture of plants.
Problem Plants and Their Control
- Cocklebur: Summer flooding with shallow water when plants are less than 12 inches. Mowing to 4 inches when plant begins to put on seed. Shallow disking any plant height. 2-4D at 1/4 to I/2 pound per acre.
- Willow, cottonwood, maple, green ash: Heavy/deep disking in summer. Double-cross disking in growing season. Mowing in fall, followed by flooding next growing season.
- Marshmallow, buttonbush: Heavy offset disking in summer, repeated 2-4 weeks. Spraying Rodeo in early growing season at rate 1 pint to 1 quart per acre. Weed wipe 50 percent Rodeo.
- Cattails, river bulrush: Burn twice in summer, flood 3 feet deep from fall through next growing season. Muskrat populations to create openings. Spray Rodeo, 1 quart per acre.
- American lotus: De-water in February or at any point before new leaves reach water surface, optional shallow disking after de-watering. Spray Rodeo, 1 quart per acre.
- Marsh smartweed (P. coccirzeum): Heavy deep disking in summer followed by herbicide treatment of regrowth. Apply Rodeo at 1 quart per acre.
- Purple loosestrife: Applying Rodeo during full bloom (July-August) in a 1- to 2-percent solution with a surfactant is the only reliable control technique.
Wood Duck Nesting Program
In the early 1900s, habitat destruction and overharvesting pushed the wood duck to the brink of extinction. Today, thanks to hunting restrictions and concern for improved nesting and brood areas, the wood duck is once again a common Missouri resident. Nevertheless, it is still important to continue to help increase the population of this beautiful bird by providing artificial nest structures in wetland areas.
Traditionally, wood ducks nested in hollow trees along streams, rivers and natural wetlands throughout Missouri. Artificial nest boxes can be placed in areas wood ducks frequent but where natural nest sites no longer exist or are limited. Lakes and ponds containing or surrounded by standing timber are ideal for nest boxes. Woodies will use boxes placed over or near water, and duckling survival is greater when the boxes are within one-half mile of water. That is because the ducklings leave the nest and walk to the nearest body of water shortly after hatching. Besides being close to a wetland, the nest box should face water.
A good wetland site for woodies should have three characteristics:
- Approximately half of the wetland should be open water, with the remainder in green plant cover.
- A supply of animal foods, such as insects and other invertebrates. These are critical, especially for ducklings less than four weeks old.
- Water that will remain until the ducklings are able to fly--eight to 10 weeks.
To install a nest box, place it above the spring high-water mark. Wood ducks will use boxes regardless of height, so attach boxes to trees no higher than is convenient for maintenance. Only a few boxes--from one to five--are necessary the first year. Add more boxes later, if the first ones are used. When making a wood duck box remember:
- Make the entrance hole 4 inches wide, whether the hole is circular or oval.
- Put hardware cloth beneath the entrance on the inside of the box so the ducklings can climb out.
- Put drain holes in the bottom of the box to prevent rain from flooding the eggs.
A successful wood duck nest-box program requires annual inspection in January or February. At this time, repair all boxes, remove old nests and add fresh material--wood ducks do not carry nesting materials to build their own nest. Put wood shavings, a mixture of sawdust and shavings, ground corn cobs or similar materials in the boxes at a 3- to 5-inch depth. Also check predator guards annually. The best way to keep predators from boxes on trees is to install metal bands at least 50 inches wide flush around the trunk; for boxes on posts, use an inverted metal cone below the box. Make sure you remove overhanging limbs that are close to the box. Black snakes and raccoons can use these overhanging limbs to approach nest boxes, making predator guards worthless.
A design for a wood duck box is available from the Conservation Department. Follow the instructions closely because the specifications provide guidelines to ensure that wood ducks using the structures will have the best opportunity for nesting success.
Giant Canada Geese and Wetlands
Restoration of giant Canada geese in Missouri began during the late 1940s and early 1950s. Initial restoration attempts occurred on Conservation Department lands but was later expanded to private lands at the request of private landowners. The primary method used during restoration was to relocate groups of 6- to 9-week-old goslings. The goslings would usually remain in the general location where they learned to fly, and it would become their home area where they would later nest.
Brood-rearing takes place on or near permanent water such as lakes, rivers or large permanent wetlands. Goslings are flightless for about 10 weeks and are restricted to feeding areas within walking distance of water. Geese use a variety of wetland plants for food; but compared with ducks, they are primarily grazers of mowed or grazed upland grasses. Pastures are commonly used in rural areas, and the manicured and fertilized grasses of lawns and golf courses are highly preferred in urban settings. During late summer and fall, the diet of geese includes more seeds. Geese are adept at stripping seeds from mature heads of grasses such as bluegrass and crab grass. During fall through early spring, agricultural crops such as corn, wheat, and milo become important food sources.
Public viewing and hunting of giant Canada geese is now available throughout the state. However, positive aspects of increasing numbers of geese are offset by a growing number of complaints. Owners of private ponds and wetlands, especially near urban locations, should be aware that actions to encourage Canada geese can often become too successful, resulting in more geese than desired. The use of artificial nesting structures and practices such as feeding birds by hand can result in future problems, which is why the Conservation Department does not recommends these practices. Landowners who provide good wetland management practices will likely have geese use their wetland during a portion of the year, but hopefully in numbers that are in balance with the surrounding habitats.
Management of Wetlands for Shorebirds
In addition to waterfowl, several other groups of birds are frequently associated with wetlands. Among these are shorebirds, which are represented in Missouri by more than 40 migrant species. Shorebirds, such as dowitchers, sandpipers and yellowlegs, typically have long, somewhat flexible bills for picking and probing for food and fairly long legs for wading in shallow water.
Although four shorebird species--killdeer, upland and spotted sandpiper and American woodcock--regularly nest throughout Missouri, none of the four nests in wetlands. Therefore, management activity should be directed toward providing feeding and resting habitat during spring and fall migration, rather than during the breeding season.
The food habits, feeding behavior and habitat requirements of shorebirds differ from those of migrant waterfowl and warrant some special consideration in the design and management of wetland areas. Most shorebirds prefer feeding areas that include shallow water up to 3 inches deep and exposed, bare mud flats containing short, sparse vegetation. Shorebirds migrate later in the spring and earlier in the fall than most waterfowl. Therefore, in the spring, the most effective strategy is simply keeping the same water level throughout the winter, followed by a gradual drawdown to expose only the most elevated areas during the last week of March and the first week of April. Shorebird migrations usually continue through the first week of June. This spring-management sequence is compatible with waterfowl, since deeper water habitats are available during peak duck migrations in late February or March. The shallow areas created by the initial drawdown for shorebirds also are attractive to most late migrant puddle ducks, such as shovelers and teal.
The fall migration begins in midsummer and requires a different strategy than used in the spring. Impoundments that often contain water in the spring are dry and covered with vegetation at the beginning of the fall migration. Disking, followed by shallow flooding in July, will provide excellent shorebird areas. Disking reduces the dense summer vegetation, creates bare soil and exposes insects found below the surface. Flooding up to a 3-inch depth creates a habitat that is used almost immediately by migrant shorebirds.
The major problem of fall shorebird management is maintaining high-quality habitat throughout the lengthy migration. Solitary and least sandpipers arrive by July 1; the long-billed dowitchers and dunlins persist until the water freezes, often in early November. If two or more impoundments are available, one should be flooded early in July, the other in September. The following criteria must be considered when selecting a site and developing it:
- Sites on rich bottomland soils offer the greatest potential.
- Sites containing areas of porous sands should be avoided.
- Impoundments as small as one to two acres can be successfully managed for migrant shorebirds; however, larger areas can be managed more efficiently for shorebirds and will provide habitat for migrant waterfowl at the same time.
- Because the best water depth for feeding shorebirds is three inches or less, levee heights should not be as great as those for waterfowl marshes.
- The depth of the water should be sufficient to allow for the gradual drawing down over the period from late March through the first week of June.
- The drawdown rate must be based on the available water supply, the slope of the ground and the evaporation rate. Care must be taken to ensure that water is not released so rapidly that it creates premature drying while migrant birds are still present.
- A dependable source of water must be available for July impoundment flooding for the late summer and fall migration period. The water requirements may be met by pumping from a well, stream, nearby lake or higher reservoir.
- Several types of water-level control structures are possible, but whichever one you choose, make sure it allows you to change the water level in increments as small as one-half inch and to rapidly and completely drain the impoundment. A stop-log type of control structure is best. It allows changes in water elevations by adding or removing fitted boards of varying thicknesses.
- The presence of raised hills or mounds within an impoundment increases the attractiveness of the area for shorebirds, because of the presence of drier sites for resting and preening and a greater shoreline area for feeding.
- If possible, large impoundments should be subdivided so that several water depths and management strategies are possible, resulting in greater wildlife diversity. Interior levees should be constructed along contours, preferably at 6-inch contour intervals.
Mammals in Wetlands
Muskrats thrive in wetlands. Their feeding habits can help control the amount of open water and vegetation in a wetland, but can also destroy the aquatic vegetation on which they and other wildlife depend. Trapping can help control muskrats and prevent destructive burrowing by these animals.
There are several kinds of mammals that thrive in wetlands. The two that have the most influence on wetland plants and, hence, on the entire ecosystem are the muskrat and beaver.
Muskrats primarily feed on aquatic plants. Their feeding habits can help wetland managers maintain the proper proportion of open water and vegetation for waterfowl. Too much muskrat activity, however, can destroy the aquatic vegetation on which they and other wildlife depend. Fortunately, such "eat-outs" are not common in Missouri.
Because the muskrat's reproductive capacity is great, in most aquatic environments the animal can withstand heavy trapping. Muskrat trapping helps create and maintain the proper habitat for wildlife and the fur from this extremely renewable resource is a valuable product. Perhaps the muskrat is most troublesome because of its digging and burrowing. Many marsh-dwelling muskrats live in lodges made from marsh plants, but in man-made wetlands, ponds and creeks, bank burrowing is normal. Fluctuating water levels aggravate burrowing problems by forcing the animals to continually dig to keep their living quarters above the water level. Vehicles or livestock can collapse the burrows, further damaging the levee or dam. Trapping is the best tool for controlling muskrat damage in severe burrowing situations. When animals are taken from bank burrows, fill the burrow and the den itself with soil so another muskrat won't move in.
Beavers can also have a major influence on wetland areas. During warm seasons beavers feed on aquatic plants but switch to a diet of bark during the fall and winter.
Known for their engineering ability, beavers create their own impoundments with dams made of sticks and mud. They also create channeled runways to allow them access to shallow areas. Beaver activities can complement managed wetlands; their impoundments create attractive waterfowl habitat.
As was the case with muskrats, too many beavers or beavers in the wrong areas can cause problems. Permanent flooding from beaver dams can destroy valuable trees. Extensive bank burrowing may cause problems similar to those caused by muskrats, except on a larger scale. The animals might also block drainage and water-control structures, which would interfere with agricultural activities.
Beavers can be controlled by trapping, but, unlike the muskrat, beaver reproductive capacities are not extremely high and precautions are necessary to prevent elimination of a colony. Limiting the catch is one way to ensure the beaver's continued presence. A previously untrapped colony led by a mature 3-year-old, can normally tolerate an annual harvest of three or four animals each year without jeopardizing the future of the colony. Beaver colonies are not permanent. When food resources dwindle, the animals will move to a new site. An advantage to limited trapping in beaver colonies, where their activities are beneficial, is that the annual removal of some animals will lengthen the life expectancy of the colony by reducing the rate at which they deplete the available food.
Managing Wetlands: Invertebrates in Wetlands
Invertebrates play a vital role in all wetland communities. They provide an important component in the food web, recycle nutrients and contribute to the breakdown of organic matter. Waterfowl, shorebirds and herons select invertebrate prey during high-protein and calcium-demand periods, such as egg-laying time. Several fish species feed almost entirely on aquatic insects, and raccoons often feed on crayfish during drying conditions in wetlands. True aquatic invertebrate organisms include crayfish, dragon flies, damselflies, mayflies, midges, water-boatmen and snails. Organisms found in moist, exposed soils include ground beetles, pirate spiders and diptera (fly) species.
The amount of invertebrates in wetland systems can vary depending on management practices. Moist-soil management produces excellent habitat for numerous mammals and birds as well as for many species of invertebrates. In this management technique, drawdown and refolding releases nutrients from the soil, which encourages robust stands of emergent vegetation, important as substrata for dynamic populations of invertebrates. Early summer drawdowns concentrate invertebrates, resulting in optimum feeding habitat for young waterfowl, shorebirds and herons.
Permanently flooded wetlands also provide important invertebrate habitat when water clarity allows aquatic plant growth. Submergent and emergent aquatic plants provide places for invertebrates to hide, cling to, graze and lay eggs. Although the populations of invertebrates supported by these wetlands are not as dynamic as those produced during moist-soil management practices, they do provide habitat for many invertebrates important to a balanced wetland community.