Source-population characteristics affect switchgrass biomass but not community biodiversity or productivity in establishing prairies

Background/Question/Methods

Successful restoration requires balancing trade-offs between adequate establishment and aggressiveness in restored populations. Poor establishment can cause restoration failure, especially if a site is subsequently colonized by exotic species. Aggressive establishment by restored populations may limit colonization by exotics but may also decrease biodiversity in restored communities. The outcome of these trade-offs may be affected by population-source characteristics including the intensity of artificial selection and the number of source populations used in developing restoration germplasm. Determining the relationship between these population-source characteristics and the establishment-aggressiveness trade-off is of particular importance for switchgrass (Panicum virgatum). This warm-season native grass is a common component of prairie restorations and is being developed as a biofuel feedstock. Using eleven commercial switchgrass strains, we investigated the extent to which artificial selection (cultivar, ecotype) and source-population number (one, multiple) affected (1) alpha diversity in establishing prairies, (2) community productivity, and (3) switchgrass establishment, persistence, and productivity. We addressed these questions using a three-year, multi-site common garden experiment in which switchgrass was seeded at a single density into experimental, establishing prairie communities.

Results/Conclusions

After three growing seasons, we found no evidence that switchgrass source-population characteristics affect community species richness, evenness, or aboveground biomass. However, artificial selection, source-population number, and site significantly affected the switchgrass proportion of aboveground community biomass. Cultivars derived from single- and multiple-source populations comprised 14.5% and 6.4%, respectively, of total biomass at the St. Paul (MN) site. Single- and multiple-source ecotypes at this site comprised 9.5% and 3.1% of biomass. At the Waseca (MN) site, multiple-source strains comprised approximately 1.2% of community biomass for both cultivars and ecotypes, whereas single-source strains comprised <1% of community biomass. In contrast to these differences in biomass, source-population characteristics did not significantly affect switchgrass establishment or persistence over three growing seasons. These results suggest that (a) differential growth rather than mortality may be responsible for differences in productivity among source-populations of switchgrass, (b) artificially-selected switchgrass strains do not significantly reduce community biodiversity or productivity when seeded at the densities used, which (c) may be insufficient for establishment of switchgrass ecotypes in prairie restorations.