Climate is a critical driver of grassland structure and function. Grasslands occur in areas that are prone to occasional drought and are characterized by highly variable patterns of rainfall, both between (inter-annually) and within (intra-annually) years. North American grasslands were formed by climate changes originating during the Miocene-Pliocene transition, and their present day distributions depend on regional temperature and precipitation gradients, as well as periodic extremes (e.g., droughts). Research at the Konza Prairie (KNZ) LTER site is addressing to the role of natural climatic variability on a broad range of ecological processes and interactions. For example, analysis of climate data and long-term records of plant productivity have provided insights into critical climate periods during the year that have the greatest impact on plant growth or flowering. Comparisons of KNZ data with other sites has demonstrated that variability in precipitation affects productivity more in grasslands than in other North American biomes. However, results based on the climate of the recent past may not reflect responses to a warmer and more variable future climate. To address the impacts of future climate change, we have designed experiments that allow us to manipulate patterns and amounts of rainfall and temperature to simulate future climates.
For the Central Plains, mean temperatures are predicted to increase and rainfall is expected to become more variable and extreme, with increased frequency of large rain events and extended droughts. Our research is addressing these two important aspects of climate change, and their interactions, within a unique experimental facility (the Rainfall Manipulation Plots (RaMPs)) capable of simultaneously altering rainfall timing and temperature over plots of native prairie. The RaMPs facility includes shelters that allows for replicated, experimental manipulation of the timing and quantity of rainfall. We use infrared lamps to increase the temperature of smaller plots nested within the RaMPs shelters. The RaMPs experiment is one of the longest running climate change experiments in the world and a unique field experiments focused on the consequences of changes in climatic variability (precipitation) as well as interactions with predicted shifts in climatic means (temperature). Results to date have demonstrated that a repackaging of rainfall into fewer larger events results in increased plant water stress, reduced plant productivity, altered soil C and N cycles, and potential changes in the genetic composition of the dominant grasses. We will continue to assess the long-term legacy of these changes in ecological processes, as we begin the next phase of the experiment to assess how long-term exposure to a more variable climate influence the ability of these grasslands to respond to, and recover from, a severe 2-year drought.