Tallgrass prairie restoration has been practiced for more than 75. years, yet few studies have systematically tested restoration methods over large geographic regions with the intent of refining methodology. In this study, we used three planting methods (dormant-season broadcast, growing-season broadcast and growing-season drill) fully crossed with three levels of seed species richness (10, 20, and 34 spp). We replicated the study on nine former agricultural fields located from east-central Iowa (Neal Smith National Wildlife Refuge) to northwestern Minnesota (Litchfield, Fergus Falls and Morris Wetland Management Districts), USA, within the northern tallgrass prairie biome. Objectives were to evaluate the relative influences of planting method, seed mix richness, and their interactions, on (1) planted cover (both total and by guild) and richness, (2) exotic species cover, and (3) non-planted native species cover. Optimal techniques varied between the two study areas: the dormant broadcast method produced greater cover of planted species at the Minnesota sites and the growing-season drill method produced greater cover of planted species at Iowa sites. The dormant broadcast method strongly favored establishment of perennial forbs while the growing-season drill favored warm-season grasses. Although increasing richness of the seed mix produced greater planted species richness, this did not result in greater resistance to exotic invasion. We conclude that, if planting during the growing season, drilling seed is preferable to broadcasting, but if the choice is between broadcasting seed in the dormant or growing season, the dormant season is preferred.
Bibliographical noteFunding Information:
We thank the dedicated staff and volunteers of the participating Refuge and Wetland Management District stations who helped with plot layout, site preparation, seeding, mowing, and vegetation monitoring. Amy Symstad, Susan Galatowitsch and three anonymous reviewers provided helpful comments on earlier versions of the manuscript. This work was supported by U.S. Fish and Wildlife Service Region 3, U.S. Geological Survey Science Support Program and Northern Prairie Wildlife Research Center. Use of trade names does not imply endorsement by the federal government.
- Exotic species
- Perennial forbs
- Restoration methods
- Tallgrass prairie
- Warm-season grasses