Restoration of C4 grasses with seasonal fires in a C3/C4 grassland invaded by Prosopis glandulosa, a fire‐resistant shrub

Abstract

AbstractQuestions: Can prescribed fire restore C4 perennial grasses in grassland ecosystems that have become dominated by fire‐resistant C3 shrubs (Prosopis glandulosa) and C3 grasses? Do fires in different seasons alter the direction of change in grass composition?Location: Texas, USA.Methods: We quantified short‐ and long‐term (12 yr post‐fire) herbaceous functional group cover and diversity responses to replicated seasonal fire treatments: (1) repeated‐winter fires (three in 5 yr), (2) repeated‐summer fires (two in 3 yr), and (3) alternate‐season fires (two winter and one summer in 4 yr), compared with a no‐fire control.Results: Summer fires were more intense than winter fires, but all fire treatments temporarily decreased Prosopis and C3 annual grass cover. The alternate‐season fire treatment caused a long‐term increase in C4 mid‐grass cover and functional group diversity. The repeated‐summer fire treatment increased C4 short‐grass cover but also caused a long‐term increase in bare ground. The repeated winter fire treatment had no long‐term effects on perennial grass cover. Mesquite post‐fire regrowth had increasingly negative impacts on herbaceous cover in all fire treatments.Conclusions: Summer fire was necessary to shift herbaceous composition toward C4 mid‐grasses. However, the repeated‐summer fire treatment may have been too extreme and caused post‐fire herbaceous composition to “over‐shift” toward less productive C4 short‐grasses rather than C4 mid‐grasses. This study provides some of the first long‐term data showing a possible benefit of mixing seasonal fires (i.e., the alternate‐season fire treatment) in a prescribed burning management plan to restore C4 mid‐grass cover and enhance overall herbaceous diversity.