COS 157-3 - Interactive effects of drought and erosion push the thermal limits of grasses on the shortgrass steppe

Background/Question/Methods

The shortgrass steppe (SGS) of Eastern Colorado is dominated by C₄ perennial grasses, which heavily rely on below ground meristems for the next year’s production. Because these meristems are found in the crown tissue below the soil surface, they are generally protected from aboveground disturbances like fire, grazing, and heat waves. However, erosion can expose the crown tissue and roots to a harsher microclimate than beneath the soil surface. A notable example is that the soil provides insulation around the crown tissue preventing it from reaching the thermal limits of the meristems during fires and heat waves. To investigate the impacts of erosion on the meristems, we quantified the erosion severity in under multiple grazing intensities by separating the severity into classes and then quantified the potential for tiller production for each erosion severity class. We also analyzed several climatic variables to understand what is driving erosion and surface temperatures on the SGS.

Results/Conclusions

Although fires have been commonly studied in grasslands, the intense solar radiation received by the SGS can also lead to high temperatures at the soil surface. The surface temperature on the SGS have been recorded at temperatures over 70°C during years with low precipitation. These low precipitation years are also accompanied with limited aboveground production. Meaning that any crown tissue that has been eroded likely lacks the shading effects of the canopy and can also experience temperatures up to 70°C. Exposure to this temperature, even for a limited amount of time, has been shown to be lethal to the meristems, substantially contributing to the lag effect that is observed when grasslands are recovering from droughts.