Background/Question/Methods Human activities are quickly changing global climate, and scientists are faced with the challenge of predicting how ecosystems will respond. As part of a Distributed Graduated Seminar through the National Center for Ecological Synthesis, we examined plant functional traits as a means of predicting plant community responses to altered precipitation patterns at the Konza Prairie Long Term Ecological Research (LTER) station. Grasslands cover as much as 36% of the terrestrial land surface, sequester carbon in their soils, support large numbers of the world’s remaining megafauna, and are economically important. Global change from expected increases in green house gases is predicted to alter global and regional precipitation regimes, and grasslands may be highly susceptible to changes in both rainfall amount and variability. Using data from a long-term (1991-2006) irrigation experiment at the Konza Prairie Biological Station in northeastern Kansas designed to remove water limitation from tallgrass prairie, we examined the effects of water addition on plant community composition, structure and dynamics. Four treatments were established: upland control, upland irrigated, lowland control, and lowland irrigated. Plant species abundances were recorded and an extensive list of qualitative traits was compiled from the primary literature.
Results/Conclusions A PCA ordination of plant species in trait space showed little overall differences in trait response to irrigation or topographic position. Essentially, all treatments were dominated by C₄ clonal, perennial tall grasses. After 16 years of treatment, irrigation had little effect on species richness or total productivity. However, the relative abundances of functional groups (e.g., C₄ grasses, forbs) appear to be affected by precipitation. The ratio of grass cover to forb cover greatly decreased in the irrigated plots compared to control plots for both upland and lowland. No significant differences were found between uplands and lowlands across time. Preliminary results suggest that an increase in precipitation will cause an increase in forb abundance relative to total cover. This may drastically affect the ability of mesic tallgrass ecosystems to support large grazing herds and may have detrimental economic and biodiversity impacts.