Can prescribed fire be used to manage a C4 invasive grass in a C4 grassland?
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Invasive species control is most difficult when the invasive species and native species community have many physiological and morphological traits in common. I tested the hypothesis that the careful timing of prescribed burns can be used to target the non-native C4 perennial grass KR bluestem (Bothriochloa ischaemum) while minimizing collateral damage to the native C4 perennial grass little bluestem (Schizachyrium scoparium). I burned individual plots containing bunches of either KR bluestem or little bluestem six times between June 2011 and January 2012 inside a 46 cm diameter steel barrel. To assess recovery, I counted the first cohort of tillers resprouting immediately after each burn as well as all live tillers on a common date in spring 2012. To assess burn damage more directly, I also counted tiller numbers in plots that were clipped but not burned on the same days. To identify potential physiological or environmental drivers of burn damage, I also recorded the phenological index, their water potentials and biomass at burn time, as well as fire temperatures and mean temperature and precipitation before and after treatments. Diverse covariance models were evaluated through AIC analysis. Analyses indicated that KR bluestem had consistently greater reductions in tiller growth due to burning compared to little bluestem. Date of burning did indeed affect the spring tiller count and indicated that, for both species, the June 2011 burn was most damaging, the January 2012 burn least damaging. The best model (lowest AIC score) average biomass at burn time to have significantly negative effects on recovery growth in KR bluestem. By contrast, plant condition did not predict recovery growth of little bluestem, but there was a small negative effect of higher environmental temperature post treatment. The experiment supported my main hypothesis that careful timing with respect to the physiological state of the invasive species can be an effective tool for invasive grass control.