Period: January 30, 2005 – April 15, 2010
Objectives: The dominant paradigm for prairie reconstructions has been to use tillage for seed bed preparation and plant seeds, commonly on sites recently removed from row cropping and therefore characterized by bare ground without significant cover of perennial native or non-native species (Morgan 1997). However, in cases where it is desirable to avoid severely damaging components of the existing vegetation, other methods must be pursued. The practice of introducing seed into existing turf of established vegetation is known as interseeding. The Tallgrass Restoration Handbook (Packard and Mutel 1997) and other publications (Packard 1994; Foster 2001) have addressed interseeding on degraded remnant prairies and cool season grass fields; however, interseeding wildflowers and other forbs into established native warm season grass stands has been poorly studied. Our previous research indicates that forbs have great difficulty becoming established in native warm season grass stands (Kindscher and Tieszen 1998). While one justification for using the interseeding method is to retain the established warm season grass species, the biomass density of a pure warm season grass stand is a very competitive environment for the establishment of forb seedlings. The dense growth and thatch of the grasses limits the amount of light reaching the soil surfacefor germination and seedling establishment, and the extensive root structures limit the availability of moisture and nutrients in the soil for development and growth of young forbs. Therefore, the goal of interseeding forbs into a warm season grass stand is to use a disturbance regime that inhibits the growth and vigor of the established grasses without causing extensive mortality, thus creating a more favorable environment for the establishment of forb species.
When the vegetation and thatch of an area to be overseeded is dense enough to limit the amount of light reaching the soil surface, as is the case in an established warm season grass planting, the accepted remedy is to conduct a prescribed burn. The increased soil exposure following prescribed burns also improves seed to soil contact. Prescribed burns conducted during the summer, at the time when warm season grasses are investing their energy into reproduction, have been demonstrated to reduce the vigor and dominance of warm season grasses and increase plant diversity by favoring subdominant species (Howe 1999, Copeland 2002). While these experiments have demonstrated the role of summer burning as a dominance-reducing measure in established prairies and restorations, they have not directly investigated the reduction of native grass dominance for the enhancement of forb interseeding.
Mowing for 1 or more years following seeding is another common practice for facilitating seedling establishment in restorations by reducing the shading effect of established vegetation (Ross and Vanderpoel 1994; Packard 1997). This
approach is commonly applied to decrease annual weed cover in “plow and seed” restorations, but it is also used to reduce shading by dominants when interseeding.
Shallow disking and the use of grass specific herbicides are existing approaches to decreasing the dominance of warm season grasses for the specific purpose of forb interseeding in established stands. Light disking at a depth of no more than 3–4 inches following a burn has led to observations of increased forb abundance and diversity (Anon. 2001). The application of the grass-specific herbicide Poast or Poast-Plus in the spring following a summer burn, as the warm season
grasses are ending dormancy, has successfully increased forb establishment in warm season grass stands (Randy Arndt, personal communication, 2004).