Fire season and simulated grazing differentially affect the stability and drought resilience of a C4 bunchgrass, C3 bunchgrass and C4 lawngrass

We used a fully factorial experimental design to examine the effects of fire season, simulated grazing and their interaction on the temporal stability (year-to-year variation in production) of the C4 bunchgrass, Bouteloua curtipendula, the C3 bunchgrass, Nassella leucotricha, and the C4 lawngrass, Buchloe dactyloides. Treatments included three levels of fire (winter fire, summer fire, and no fire) and two levels of grazing (simulated grazing and no grazing). Additionally, a severe drought during the fourth year of the five year study allowed us to examine each species’ post-drought resilience. In the southern Great Plains, USA, these three perennial grass species are economically and ecologically important; each species is a dominant member of their functional group and important as livestock forage. Temporal stability and drought resilience of the C4 bunchgrass, Bouteloua, were significantly greatest in the summer fire treatments. In contrast, temporal stability of the C3 bunchgrass, Nassella, was significantly greatest in the no-fire treatments and its drought resilience was significantly greatest in the no-graze treatments. Temporal stability and drought resilience of the C4 lawngrass, Buchloe, were not affected by any of the treatments. The contrasting effect of fire on the C4 and C3 bunchgrasses is consistent with the hypothesis that fire favors C4 over C3 grasses due to differences in post-fire soil conditions such as increased temperature, reduced moisture and reduced mineralizable nitrogen.