Trends in soil microclimate and modeled impacts on germination timing in the sagebrush steppe

Abstract

AbstractPast and projected changes in climate affect soil microclimate, impacting seeds that use soil moisture and soil temperature as cues for germination. Seed germination and plant establishment are among the most important processes regulating plant community assembly in response to climate change. Changes in germination timing expose seedlings to new abiotic and biotic risk factors that can affect recruitment success. Species with seed dormancy strategies to avoid harsh winter conditions could experience more mortality if changes in germination timing cause early germination and subsequent exposure to freezing conditions. We analyzed soil microclimate trends in the sagebrush steppe from 1979 to 2017 using a soil physics model (SHAW) and calculated the germination timing of native species used in restoration efforts with wet‐thermal response curves from lab trials. We applied the germination curves to modeled soil microclimate at 10 sites in the sagebrush steppe. Our results indicate that warmer and wetter fall seasons have become more prevalent and will likely lead to accelerated germination of several native restoration species in the sagebrush steppe. Changes to spring soil conditions favor slightly more germination in early spring, but strong trends of earlier onset of spring soil conditions were not evident. Trends in climate have created drier and warmer summer seedbed conditions, likely to increase stress on seedlings. Historic cycles of alternating slow or fast germination appeared less frequently during the last 12 years of the study (2004–2016). Seedbed microclimate trends will likely impact seedling establishment by altering germination timing and exposing seeds to more harsh abiotic conditions, likely resulting in decreased recruitment of native species and increased abundance of invasive annual grasses.