Monday, July 13, 2009

US FISH AND WILDLIFE SERVICE ARTICLE ON prairie wildflower restoratioin

Prairie flowers – Photo credit: U.S. Fish and Wildlife Service / Shawn May

Nearly 99% of the native tallgrass prairie has been lost to the plow and to development in the Detroit Lakes Wetland Management District, and this loss of habitat directly impacts many species of wildlife. Grasslands provide shelter for birds, mammals, reptiles, and insects. Species like greater prairie chickens, marbled godwits, short-eared owls, bobolinks and other song birds require large tracts of grasslands to make their homes. All species of ground nesting birds like waterfowl, pheasants, and songbirds need grasslands in which to build and conceal their nests.

The native grass species found in the Northern Tallgrass Prairie vary in height, from side-oats grama (that is about 1 foot tall), to prairie cordgrass and big bluestem (which can reach 7 feet tall). These plants develop root systems that are sometimes twice as long as the plants are tall. Because of this dense root system, these plants form sod that has a tremendous capacity to absorb run-off and rain water. The plants can take up chemicals and nutrients that are carried into the grassland by run-off thus filtering the water that flows through a tract of grassland.

Grassland Restoration and Management

When a new tract of land is acquired, it has usually been farmed, and a majority of the wetlands frequently have been drained. Due to the high density of wetlands in many areas of the District, the uplands are seeded to native grasses and forbs (wildflowers) first and allowed to establish before the wetlands are restored. The District harvests most of the needed seed from local native prairies which are diverse and of local origin. We also purchase some local origin grass and forb seeds to diversify our seed mix.

Seeding is done in the early spring, when the snow is melting and the sun's rays are getting warmer. The prairie mix of seed is generally broadcast into soybean stubble, however grass stubble and burned grass (ash) is also sometimes used as a seedbed.

Snow seeding – Photo credit: U.S. Fish and Wildlife Service / Les Peterson

A diverse seed mixture is important because the wildflowers provide food for many species of insects. Grassland birds and many other species of wildlife feed on the insects found in these prairies. Plant species diversity also provides variability in the grassland structure. Some wildlife species need dense grasses overhead and passageways near the ground; others like shorter, open areas in a grassland. Increased plant diversity provides better cover, nesting habitat and food for a larger variety of wildlife species.

Many prairie seedings would turn into a beautiful stand of grasses and wildflowers if given enough time, and the proper management to allow this to occur. Management actions often prescribed when a grassland is establishing, such as repeated weed clipping or spraying grasslands with chemical, can eliminate the diversity from a prairie seeding for the future. In the first couple years of growth, native plants grow downward as much, if not more, than they grow upwards. Having a deep root system allows prairie adapted plants to withstand severe droughts. Because native plants put so much energy into root growth when a grass stand is establishing, thistle will sometimes take advantage of the lack of competition for daylight. During this important time for the new seeding, weed control such as repeated clipping or chemical application can be detrimental to the long-term diversity of the grass stand and may actually perpetuate the problem. Management of weeds on the District focuses on the long-term control of invasive weed species in order to control the spread of noxious weed seed across the countryside. If properly managed, a diverse native plant community that has laid its roots deep, will out-compete many weed species for the long term. After a seeding has been established, it is difficult for many weeds to invade these dense native grass stands with their robust root systems.

Rarely do weeds invade native prairies or established native grass seedings; however, this can happen with some species of particularly invasive weeds (eg. crown vetch). Weed species can also invade grass seedings when soils are disturbed or seeded plants are sparse. When necessary, the District uses an integrated approach to control invasive plants in the short-term, with the goal of long term control being provided culturally through the establishment of a diversified grassland plant community.

Utilizing cultural, mechanical, chemical, and biological control techniques in combination is often more effective than using a single control technique. The District has used new technologies, such as a wetblade© mower that combine mechanical and chemical control into a single operation. An example of an effective biological control is the use of flea beetles for leafy spurge control. These insect species are native to Eurasia, where they naturally controlled spurge populations. Flea beetle larvae feed on the roots of the spurge plants, which keeps them from growing and may eliminate them completely from a grassland when conditions are ideal. Using its' natural insect predator, biological control can be a cost effective and species specific method of weed control. Research continues on biological controls for other problem weed species such as spotted knapweed and Canada thistle.

Wetblade mower – Photo credit: U.S. Fish and Wildlife Service / Kent Jensen

Fire is typically not used on a new seeding until the fifth to seventh year after seeding in order to allow the new plants time to establish themselves. After that initial period, a fire rotation of 3 to 5 years is used in order to stimulate the production of seed.

When fire has been absent from a tract of grassland for many years, trees and brush can invade. The Northern Tallgrass Prairie on average receives enough rain to support trees, but historically trees did not survive here unless they were near rivers or lakes. Oak savannas are another habitat type found in the District where invading trees are altering the landscape. Frequent disturbance from fire, bison grazing, and drought allowed these prairie communities to dominate the landscape. With the elimination of these periodic disturbances over the past 100 years, tallgrass prairies and hilltops once covered with scattered oaks and prairie grasses have gradually grown up in green ash, Siberian elm, and cottonwoods. In the portions of our District that were historically prairie or oak savannas, we are actively eliminating invading or previously planted trees using mechanical cutting and prescribed fire.

Last updated: July 9, 2008

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