The 2007 Regional report by the Intergovernmental Panel on Climate Change predicted that the central grassland region of North America is very likely to warm substantially during the twenty first century. Modelers are less certain about changes in the timing and amount of precipitation in the region. Our research examines how changes in plant available water will affect critical biological processes in the central grassland region of North America, specifically comparing a site at the Shortgrass Steppe LTER to a site on the mixed grass prairie near Hays, KS. Changes in plant available water can affect key ecological processes by altering plant species assemblages, functional type, and spatial arrangement of species. Our research focuses on the response of plant species composition and community structure in plots that receive different precipitation treatments. The importance of grasslands in North America and worldwide provide a strong argument for the urgency of understanding the potential impact of climate change on these systems.