Plant invasions may change natural fire regimes by increasing fuel loads and fuel bed continuity, which may alter fire behaviors such as intensity, rate of spread, and extent. Fires can subsequently promote additional plant invasions by exposing soil and releasing nutrients, resulting in a positive feedback between plant invaders and fire. We are examining the interaction between fire and the invasive annual grass Microstegium vimineum (Japanese stiltgrass), including differences in fire behavior in invaded and uninvaded areas and the dynamics of invasions in response to fire, by evaluating large-scale prescribed burns at Big Oaks National Wildlife Refuge (BONWR) in southern Indiana. Microstegium invasions produce a widespread, dense layer of fine fuels following plant senescence. This unnaturally continuous and flammable fuel bed may result in abnormally intense fires. Increased fire frequency and severity in invaded areas may cause greater damage to native vegetation, unpredictable prescribed fire behavior, and further invasions.

Results/Conclusions

Our results indicate that fuel loads in areas invaded by Microstegium at BONWR are 24.8% greater than in areas that have not been invaded, primarily due to the biomass of the invader. Across eight field sites where Microstegium was experimentally removed, there was on average 42% less fine fuel. These differences in fuel abundance and continuity may significantly increase fire temperatures, the rate of fire spread, percent area burned, and damage to native plants. We are evaluating the response of four native tree species to fire in invaded and uninvaded areas to gauge how invasions may mediate the effects of fire on tree regeneration. Previous observations indicate significantly increased rates of invasion in burned areas, likely due to exposure of quality germination sites and reductions in competitive native species. Our results will provide valuable information to land managers regarding the effects of Microstegium invasions on fire behavior, the impact of fires on invasion dynamics, and how to control invasions in forests exposed to fire.