Invasions of forests by functionally unique species, such as non-native grasses, can profoundly affect ecosystem functioning and reduce forest resilience to disturbances, especially fire. Fire is widely used to manage forests, often with the goal of increasing understory biodiversity, and promoting ecologically and economically important tree species. However, by altering fire regimes, grass invasions may make it difficult to achieve these goals. Here, I bring together several studies on Microstegium vimineum, a widespread non-native invasive grass, to illustrate how grass invasions can affect forest resilience through a positive feedback with fire. In doing so, I highlight how expanding our spatial and temporal perspectives can lead to a fuller understanding of how grass invasions affect forest resilience.
Results/Conclusions
In temperate forests, grass invasions can dramatically increase the intensity and extent of fire by enhancing ecosystem flammability. These changes increase soil nutrient availability, decrease the abundance and diversity of native species, and expose bare ground, all of which can promote further invasions and lead to a positive disturbance-mediated feedback. Invasion may also increase the susceptibility of forests to fire-induced nutrient losses by shifting a greater proportion of ecosystem nutrient capital aboveground, where it is more vulnerable to loss through volatilization by fire. At the landscape scale, however, topographically driven variation in soil moisture limits the effects grass invasion on forest resilience. Additionally, repeated fire has the potential to weaken the grass-fire feedback over time because of mismatches in the timing of nutrient release and plant nutrient uptake. These findings underscore the importance of considering feedbacks between grass invasion and fire and demonstrate that broad spatial and temporal perspectives are needed to predict the consequences of grass invasions on forest resilience.