Climate change and plant species composition and community structure in the central grassland region of North America

Precipitation and temperature are recognized as important drivers of plant community structure and function across ecosystems worldwide. The seasonality and quantity of precipitation combine with temperature to influence soil water balance, which is a primary determinant of terrestrial vegetation. Aspects of soil water balance have been shown to affect many properties of plant communities. The distribution of the earth's major biomes, for example, can be largely predicted from temperature and precipitation. Abundant evidence supports a strong relationship between actual evapotranspiration (AET) and aboveground net primary production (ANPP), and strong relationships exist between precipitation and species richness as well. Yet recent predictions of an increase in mean global temperature and changes in precipitation timing and quantity have the potential to alter terrestrial communities in novel ways by changing both the strength of abiotic controls on ecosystem processes as well as changing biotic interactions such as predation, competition, and trophic interactions in plant communities. As strongly water-controlled systems, grasslands may be particularly sensitive to predicted changes in climate. Using the central grasslands of North America as my study region, I examined how predicted changes in climate will affect soil water availability, net primary production, and species composition and community structure at study sites located in the shortgrass steppe and mixed grass prairie.;My results demonstrate that ecosystems located within the same biome may respond differently to similar changes in precipitation and temperature, primarily due to differences in community structure, interspecific competition, and patterns of soil water availability. Simulated future soil water availability revealed greater temporal and spatial changes in available water at the mixed grass prairie than at the shortgrass steppe site. Using a soil water manipulation experiment, I found that ANPP at the shortgrass steppe was insensitive to changes in soil water, while belowground net primary production (BNPP) was sensitive to changes in soil water, although the direction of the response differed between years. I observed the opposite pattern at the more mesic mixed grass prairie site. Here, there was a rapid ANPP response to the water manipulation treatments, but BNPP was insensitive to changes in soil water availability. Likewise, the shortgrass steppe plant community was fairly insensitive to manipulated soil water, while the mixed grass prairie plant community responded rapidly to manipulated soil water. The differences in community responses between my two sites highlight the importance of multi-site studies to refine our knowledge of the mechanisms and generalities of community response to climate change at the biome level.