COS 237-2 - Prescribed fire timing drives differing emergence phenology in tallgrass prairie species

Abstract: Disturbance by fire plays an important role in temperate grasslands by removing buildup of senesced plant material, stimulating grass and forb productivity, and promoting native species diversity. In tallgrass prairies in the midwestern United States, fire is typically prescribed on the shoulders of the growing season, in either early spring or late fall. Yet, the timing of fire, even when prescribed during the dormant season, can alter prairie plant community composition. Numerous studies have examined the impact of fire seasonality on the relative abundance of early- and late-flowering prairie species, but species-specific responses within that framework have substantial nuance. Spring emergence timing is an understudied aspect of plant community response to fire and one potential diver behind long-term changes in plant community composition depending on the timing of prescribed burns. To better understand how fire seasonality effects change in grassland plant community composition, we examined emergence timing and subsequent life history events of tallgrass prairie species and whether responses differed depending on flowering guild (i.e., early- or late-flowering species). We hypothesized that spring prescribed burns would delay emergence for early-flowering species when compared to fall-burned conspecifics. We further predicted that delays in emergence would impact flowering phenology. To test our hypotheses, we collected weekly data on emergence and first flowering date for eight species in plots that have been burned annually in either April or November since 2016. We also looked at soil temperature, soil moisture, and photosynthetically active radiation at the soil surface to better understand how environmental conditions that are influenced by fire impact plant responses. We found that fall prescribed burns accelerated emergence timing by up to two weeks for some early-flowering species when compared to spring-burned or unburned conspecifics, which may have implications for flowering phenology and seed production. This study suggests that emergence timing is one mechanism that drives long-term plant community responses to dormant season burns, potentially due to subsequent effects on flowering phenology and seed production.