Fire season and simulated grazing differentially affect the stability and drought resilience of a C 4 bunchgrass, C 3 bunchgrass and C 4 lawngrass

Abstract

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 C 4 bunchgrass, Bouteloua curtipendula, the C 3 bunchgrass, Nassella leucotricha, and the C 4 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 C 4 bunchgrass, Bouteloua, were significantly greatest in the summer fire treatments. In contrast, temporal stability of the C 3 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 C 4 lawngrass, Buchloe, were not affected by any of the treatments. The contrasting effect of fire on the C 4 and C 3 bunchgrasses is consistent with the hypothesis that fire favors C 4 over C 3 grasses due to differences in post-fire soil conditions such as increased temperature, reduced moisture and reduced mineralizable nitrogen.