THE ROLE OF WATER DEPTH AND SOIL-TEMPERATURE IN DETERMINING INITIAL COMPOSITION OF PRAIRIE WETLAND COENOCLINES

In this study, we examined the effects of water depth and temperature on seedling recruitment from a prairie wetland seed bank. We collected seed-bank samples from natural and restored prairie pothole wetlands in northwestern Iowa and combined them into a single sample. We examin ed seedling recruitment from this seed-bank sample in an experimental study using a factorial design of 4 temperature treatments (5 degrees night and 15 degrees day to 20 degrees night and 30 degrees day) and 3 water-depth treatments (0, 2, and 7 cm). Principal Components Analysi s showed that both water depth and temperature had significant effects on the composition of the seedling community as measured by changes i n relative stem density and biomass. Water depth had its strongest eff ects on stem density while temperature had its strongest effects on bi omass. For the 22 most common species, stem density varied with water depth for 95% of the species and with temperature for 50% of the speci es. Most species with water depth responses had lower stem counts as w ater depth increased, and for the majority of species with temperature responses stem density increased with temperature. Total, annual, and perennial species richness was negatively correlated with water depth . Total and annual species richness was positively correlated to tempe rature, while perennial species richness was unresponsive to temperatu re. In addition, species found at low elevations as adults emerged at higher rates in the deep water treatments while species that occurred at higher elevations as adults had their highest emergence rates in th e low water treatments. Our results suggest that differences in enviro nmental conditions along coenoclines can affect the initial distributi on of species emerging from the soil seed bank. Water depth sorted see dlings according to their adult water-depth tolerances, and temperatur e determined the proportion of annuals in the seedling community.