Prairies in the loess hills are dominated by little bluestem (Schizachyrium scoparium) and side-oats grama (Bouteloua curtipendula) on south- and west-facing slopes. Tall grasses like big bluestem (Andropogon gerardii), switchgrass (Panicum virgatum), and indian grass (Sorghastrum nutans) are dominant on north- and east-facing slopes and in lowlands. Cool season grasses such as junegrass (Koeleria macrantha), porcupine grass (Stipa spartea), Canada wildrye (Elymus canadensis) and Dichanthelium spp. are important as well. Many interesting forbs are also found, including many species that are at their eastern-most range limit, such as yucca (Yucca glauca) and skeleton rush (Lygodesmia juncea). Dozens of forb species are found even in small remnants (Wilsey et al. 2005 Conservation Biology), and forbs make up a large portion of the species diversity of a given site.
We have conducted studies on what determines species diversity in restored prairies of the Loess Hills at the Western Research farm near Castana. Studies looked at how native grass species identity (5 common grass species), species richness (1 vs. 5 species mixtures), and seed source (local vs. cultivar seed) might impact prairie forb recruitment following over-seeding of experimental plots (see pictures below, Wilsey 2009). It is poorly known how grass species identity influences diversity, and which species traits are associated with species diversity suppression. Measurements of species growth rates, height, and lateral spread were measured to develop a mechanistic understanding of how species impact the diversity of developing prairie communities, and in turn, how differences in diversity will impact ecosystem processes (Wilsey 2009). Grasses dominate restorations via two mechanisms: 1) by growing tall and capturing light (e.g. Panicum virgatum), or 2) by quickly filling in bare space by spreading horizontally through rhizome growth in short species (e.g. Bouteloua curtipendula). The first mechanism is widely acknowledged, but the second mechanism was reported for the first time.
Captions: Top, Sylvan Runkel preserve in Monona County, Iowa. Center, Grass plots in the first year of establishment. Plots were established by planting equal-mass seedlings. Bottom, Grass plots in their fourth year, in a year of above-average rainfall (2008). Wayne Roush is pictured.