Effects of fire timing and snow cover on tallgrass prairie plant re-emergence phenology, growth rate, and flowering.

In a time of unprecedented global change, understanding plant community responses to contemporary disturbance regimes is necessary to improve the predictability of restoration outcomes. Although fires in tallgrass prairies historically occurred throughout the growing season, contemporary prescribed fires are often conducted during the dormant season, in either spring or fall. Dormant-season burns remove vegetation and litter at different times of year, which has subsequent effects on microclimate dynamics. These dynamics may compound with projected changes in winter climate, including decreased snow cover and more variable soil temperatures. Short-term responses to microclimate conditions are most detectable early in the growing season, yet plant community metrics are often measured broadly at one or a few points during the peak growing season. Understanding how disturbance timing and a changing climate influence plant community responses through and beyond these early stages of growth is an imperative step toward improving the ability to predict long-term plant community responses during restoration. To evaluate responses to disturbance and winter climate, we manipulated fire application, fire timing, and snow depth in a tallgrass prairie restoration from 2016 to 2023, then evaluated re-emergence timing in spring and subsequent effects on relative growth rate and flowering effort throughout the 2023 growing season. Plants re-emerged earlier and grew more slowly in fall burn treatments than in spring burn and unburned treatments. Within their respective disturbance treatments, plants that re-emerged faster tended to grow faster, and relative growth rate was positively correlated with the probability of flowering. Winter snow cover was not correlated with re-emergence or growth rate, but snow removal tended to decrease the probability of flowering. Our results suggest resilience to winter climate change in the short term and demonstrate cascading effects of fire application and timing on tallgrass prairie plant phenology and fitness responses.