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In recent years, agricultural producers and non-governmental organizations and agencies have restored thousands of hectares of cropland to grassland in the Great Plains of the United States. However, little is known about the relationships between richness and seeding density in these restorations and resistance to invasive plant species. We assessed the effects of richness and seeding density on resistance to invasive and other unseeded plant species in experimental tallgrass prairie plots in central Nebraska. In 2006, twenty-four 55 m x 55 m plots were planted with six replicates in each of four treatments: high richness (97 species typically planted by The Nature Conservancy), at low and high seeding densities, and low richness (15 species representing a typical Conservation Reserve Program mix, CP25), at low and high seed ng densities. There was a significant negative relationship between richness and basal cover of unseeded perennial forbsllegumes and unseeded perennial/annual grasses, abundance of bull thistle (Cirsium vulgare), and the number of inflorescences removed from smooth brome (Bromus inermis) transplants. Invasion resistance may have been higher in the high richness treatments because of the characteristics of the dominant species in these plots or because of greater interspecific competition for limiting resources among forbs/legumes with neighboring plants belonging to the same functional group. Seeding density was not important in affecting invasion resistance, except in the cover of unseeded grasses. Increasing seed mix richness may be more effective than increasing the seeding density for decreasing invasion by unseeded perennial species, bull thistle, and smooth brome. [ABSTRACT FROM AUTHOR]

In the montane grasslands of Rocky Mountain National Park, Colorado, non-native plant species are affecting the distribution and cover of native plant species. Two exotic nitrogen-fixing Eurasian sweetclover species (Melilotus officinalis and M. alba) occur in patches that have less available nitrogen (N) and a species composition different from surrounding grassland patches. I tested whether burning sweetclover-invaded patches would increase native grass and perennial diversity and available soil nitrogen at this elevation. I burned 24 sweetclover-invaded and noninvaded field plots with a propane torch in May 1999. Burning increased species richness and ground cover. Specifically, one year later native, grass, and perennial species increased in previously invaded patches and sweetclover or other exotic species associated with sweetclover did not increase. Soil ammonium (NH4+) levels increased immediately after the burn in May, and nitrate (NO3-) levels increased later in July and August. New species appeared only in burned plots. While other methods to reduce sweetclover might remove resources, fire increases light, space, and nutrient availability for native species that, in turn, suppress the exotic species. [ABSTRACT FROM AUTHOR]

The article presents information on research papers related to grasslands. The paper "Grazing and Wildlife," by S. Clubine, published in the "Native Warm-Season Grass Newsletter," discusses the problems grazing cattle cause for grassland nesting birds. The greatest concern is nest trampling, especially in densely stocked paddocks grazed in rapid rotations. The paper "Application of the Fire-grazing Interaction to Restore a Shifting Mosaic on Tallgrass Prairie," by S.D. Fuhlendorf and D.M. Engle, published in the "Journal of Applied Ecology," compares ecologically based rangeland management with traditional management to see if either could produce a shifting mosaic of vegetation characteristic of pre-Columbian tallgrass prairie. The paper "American Prairie Overlooked No More," by S. Kinzer, published in the June 2004 issue of the journal "New York Times," highlights the Midewin National Tallgrass Prairie, the first federally designated prairie preserve in the United States. The paper "Dominance Not Richness Determines Invisibility of Tallgrass Prairie," by M.D. Smith, J.C. Wilcox, Theresa Kelly and Alan K. Knapp, published in the journal "Oikos," examines the effects of species richness and dominance on invasion by yellow sweet clover, an exotic legume, in a tallgrass prairie in Kansas.