Simulated Fire Season and Temperature Affect Centaurea stoebe Control, Native Plant Growth, and Soil (±)-catechin

Invasive species, including the non-native forb Centaurea stoebe (spotted knapweed), constitute a threat to degraded and restored native prairies. Considering the threat that C. stoebe poses to prairie ecosystems, we examined the effectiveness of fire as a control for C. stoebe and (±)-catechin, a known allelopathic compound. We conducted an experiment in a reconstructed tallgrass prairie community at Pierce Cedar Creek Institute in Barry County, Michigan starting in May 2016. Our experiment consisted of individually burning 60 1-m² plots with a propane torch to achieve high (316°C) and low (103°C) temperatures across spring and summer seasons over two years, then planting and seeding six native prairie plant species to monitor their establishment after burning. We compared the effects of the different burn treatments on the plant community by estimating percent cover and biomass of all species within each plot in August 2017. We also examined the effects of the simulated burn treatments on soil (±)-catechin levels, which we quantified using High Performance Liquid Chromatography. Centaurea stoebe was less dominant in burned plots than unburned plots, with summer-burned plots having the lowest biomass and cover. Differences in burn temperature failed to produce significantly different results. Planted native grasses increased more after spring burns than after summer burns. Preliminary findings suggest that high-temperature spring burns may indirectly reduce soil (±)-catechin levels. Overall, these results indicate that prescribed burning is an effective tool for controlling C. stoebe and promoting native species establishment in restored tallgrass prairies.