Climate Change and Tallgrass Prairies: Exploring the Interaction of Extreme Weather and Invasion in Managed Prairie Systems

Abstract

Climate change will increasingly shift seasonal timing and increase the frequency and intensity of extreme events like drought and severe wet conditions, all of which threaten to amplify other global change drivers like invasion. Consequently, understanding how conservation management actions like prescribed burning interact with climate is increasingly pressing for invasive management. Although prescribed burning has been widely demonstrated to increase native plant diversity and suppress a number of invasive species, understanding under what current and future conditions burning will be most effective remains an ongoing focus of applied prairie ecology research. Earlier springs and extended growing seasons will shift the timing and availability of resources and niche space, which may disproportionately advantage invasive species and also influence the outcome of burning. Furthermore, northern tallgrass prairies will experience intensified extreme precipitation patterns characterized by more precipitation falling in fewer events interspersed with longer dry periods and amplified evapotranspiration. Because moisture availability functions as a key determinant of prairie composition, theory and evidence suggest drought conditions will hinder invasion, whereas wetter conditions will enhance invasion. Here, I conducted two analyses exploring the effect of weather on prairie invasion dynamics from 2010-2019 in 25 observed prairie sites and 267 transects spread throughout Minnesota, USA. First, I estimated the effects of burning, start time of the growing season, and their interaction. Second, I estimated how an increase in extremely wet or dry months altered invasive abundance and influenced the effectiveness of burning. For the first analysis, I determined that burning reduced both total invasive and invasive cool season grass abundance, and that this reduction persisted over time for invasive cover but quickly waned for frequency. Additionally, I found that growing season start does indeed influence community composition but that later starts rather than earlier increased invasive abundance. For the second analysis, I found that a greater occurrence of abnormally wet months increased invasive abundance and minimal evidence that abnormally dry conditions hinder invasion. Furthermore, I did not observe additive interaction effects of drought and prescribed burning but did find that an increase in the number of wet months reduced the effectiveness of burning. Together, these results suggest that, although earlier spring timing is unlikely to be a primary mechanism driving increased invasion, more frequent extremely wet and dry months may intensify invasive dominance and hinder our ability to suppress invasion species via prescribed burning. Ultimately, I propose that future research should seek to better understand abiotic controls on invasive species’ phenologies, how precipitation seasonality influences invasive performance, and also identify potential thresholds in ecological processes to understand whether responses in community invasion dynamics are abrupt or gradual.