Climate change in the Great Plains: More extreme precipitation patterns impact ecosystem function differentially across the central US

Future climate scenarios for the central US include a shift to more extreme precipitation patterns in which growing season rainfall events will be fewer in number but larger in size.  Within this region, a strong west-east precipitation gradient (350 to 850 mm) gives rise to three distinct grassland types – the shortgrass steppe, mixed grass prairie, and tallgrass prairie – which differ strongly in ecosystem structure and function.  Aboveground net primary productivity (ANPP) is characteristically water-limited in each of these grasslands.  A shift to fewer rainfall events is likely to alter soil water availability for plant uptake via changes in rates of evaporation, transpiration, and runoff.  To investigate how ecosystem function may be impacted by shifts in precipitation patterns, we conducted a multi-site study in which growing season precipitation was manipulated through the use of small-scale rainout shelters (n=15 per grassland). Beneath these, we varied rainfall distribution through application of 12, 6, or 4 events/season, while maintaining cumulative amounts at 30-yr averages. Reducing event number had dramatic but opposite effects across the precipitation gradient.  In tallgrass prairie, a reduction from 12 to 4 events resulted in a 15% reduction in ANPP.  In contrast, an increase in ANPP of 30% and 70% was observed in short- and mixed- grass prairie, respectively, as event number decreased (but event size increased).  Data suggest that changes in precipitation patterns strongly influence soil moisture dynamics and soil water content, which, in turn, drive ecosystem function.