Comparison of Reconstructed and Remnant Prairies

Perhaps the most important question in restoration ecology is, how well can we restore a native ecosystem? To address this question, we compared restored prairies to remnants. We compared plant species diversity, net primary productivity, and community stability at several different paired sites in Iowa and Texas. Results suggested that restorations are able to establish the common native species and reduce exotic biomass to remnant levels (Polley et al. 2005, Martin et al. 2005). However, species diversity (especially species richness) at all scales remained well below remnant levels (Polley et al. 2005, Martin et al. 2005). The proportion of beta diversity can be lower (Polley et al. 2005) or higher (Martin et al. 2005) in restorations compared to remnants, depending on the amount of topographic relief, seeding regimes and patch size in recruiting plants. We also tested whether low diversity in restorations is caused by seed limitation or by a lack of disturbance by native ungulates (bison and elk) at Neal Smith National Wildlife Refuge. Results suggested that seedling emergence of rare species can be increased with a combination of seed additions and grazing.

Native cover crops and community assembly

We are conducting experiments in Iowa (Western Research and Horticulture Farms) and Kansas (Ft. Riley) that compare how prairie communities assemble and how species diversity varies among plots as a function of early-emerging plant species composition. Historical effects, dispersal limitations, or timing of disturbance can cause very different species to be initially present among patches or fields. We are testing how these differences in species identity will affect the outcome of community development. Community assembly theory predicts that different species compositions will be found depending on which species is present initially, and predicts that alternate stable states will occur. Alternatively, succession theory predicts that species composition will not vary across initial species treatments, and that species composition will converge on a small subset of species best adapted to the climate and soil conditions of the site. Neutral theory predicts that species composition will closely match the seed-mix composition. If differences in species composition are found among treatments, it would be important because this type of patchiness is what underlies beta diversity, which is expecially high in tallgrass prairies (Wilsey et al. 2005). An experiment was established in 2004 that varied the identity of the early emerging species. Species treatments were black- eyed susan Rudbeckia hirta, Canada wildrye Elymus canadensis, partridge pea Chamaecrista fasciculata, Illiniois bundleflower Desmanthus illinensis, or side-oats grama Bouteloua curtipendula, as well as a control (no initial species present). These species emerge early and have the potential to impact species diversity as prairie communities develop. Species were allowed to establish in replicated plots for one growing season before a prairie seed mix of 27 species was added. A second study includes native cover crops, timing of seeding (summer of winter), and priority effects (adding seed mix with the cover crop or in the year after). Data from our experiments will help differentiate among these important alternative hypotheses for how prairies establish. Furthermore, our results will provide one of the first experimental tests of whether native cover crops can help to establish prairies.

Prairie plots containing Rudbeckia hirta left or control right.