Seasonally Flooded Marsh

Crane nest in seasonally flooded marsh

Freshwater marshes make up the most common form of wetland in North America and provide critical habitat for a plethora of wildlife.

This habitat type, measuring approximately 17,000 to 18,000 acres, exists within a mosaic of wet meadow and open water areas. Emergent marshes are found throughout the southern Blitzen Valley, become less extensive north of Buena Vista, and occur in the southern half of the Double-O Unit. Common emergent plant species include burreed, bulrushes, cattails, sedges, rushes, and spike rushes. Refuge emergent marshes are dominated by hardstem bulrush, cattails, or broad-fruited burreed. These emergents typically tolerate fluctuations in water availability ranging from 3 feet (1 m) above to 4-5 inches (10-12 cm) below the soil surface. Submergent plants such as pondweeds, bladderworts, waterweeds, and duckweeds occur in adjacent deeper open water areas. Willow species can occur along elevated ecotones along marsh perimeters.

Wildlife species associated with these marsh habitats include greater sandhill cranes, trumpeter swans, overwater nesting ducks (diving ducks and mallards), rails, bitterns, black and Forster’s terns, coots, marsh wrens, common yellowthroats, and yellow-headed and red-winged blackbirds. Marshes provide foraging, resting, pairing, and nesting habitat for these species. Emergent vegetation in marshes provides escape cover for broods of numerous species, particularly late-season nesters such as gadwall, redhead, and grebes.

The maintenance of existing emergent communities is artificial, requiring extensive infrastructure and active water diversion. Tools such as burning, mowing, disking, and using herbicides have been used to enhance this habitat type. Herbicides are occasionally used to control invasive species within this community.

The greatest challenge associated with this habitat is maintaining an adequate prescribed fire cycle to remove excess litter, create open water areas, and generally make it more conducive to use by wildlife (e.g., nesting cranes and mallards). The two prevalent invasive species within emergent marshes are common reed and hybrid cattail. Some emergent stands in the Blitzen Valley (i.e., common cattail) have expanded and encroached into adjacent wet meadow and open water areas in the past decade, reducing habitat values for some nesting birds.