Fire and non-native grass invasion across a heterogeneous landscape in the Central Hardwoods

Abstract

Non-native grass invasions have the potential to change natural and prescribed fire regimes by altering fuels, which in turn may promote further invasion. I examined if invasion by Microstegium vimineum, a non-native annual grass resulted in a positive invasion-fire feedback in eastern deciduous forests managed with prescribed fire and how this response varied across the landscape. Using paired invaded and uninvaded plots embedded in forest stands with or without a history of prescribed fire, I quantified differences in fire intensity and fuel loads, and fire effects on M. vimineum seed bank emergence and performance. Invaded sites had less leaf litter and fine woody fuels, and increased fire intensity. Although fire reduced emergence of M. vimineum from the soil seedbank, plots with a history of prescribed fire exhibited higher M. vimineum biomass and recruitment than unburned plots the following growing season. Soil moisture strongly modulated M. vimineum response to fire, such that the positive response of M. vimineum to soil moisture was greater at sites which were burned. These findings indicate that deciduous forests are vulnerable to positive invasion-fire feedbacks, although the positive effect of fire may be less pronounced where soil moisture is limiting. The interaction between soil moisture and fire effects can inform management decisions regarding where to combine prescribed burning with intensive invasive control measures such as torching, hand pulling, and herbicide application.