Can prescribed fires restore C4 grasslands invaded by a C3 woody species and a co-dominant C3 grass species?

Prescribed fire is used to reduce woody plant invasion and restore herbaceous production and diversity in grasslands and savannas worldwide. Here we determined if a concentrated series of repeated-winter, repeated-summer, or alternate-season (winter and summer) fires in a short timeframe (“transition fires”) could catalyze the restoration of C4 perennial grasses in Southern Great Plains, USA grasslands that had become dominated by a fire-tolerant C3 woody N2-fixer (honey mesquite, Prosopis glandulosa) and a C3 perennial bunchgrass (Texas wintergrass, Nassella leucotricha). We applied transition fires over a 5-year span, and maintenance fires on a portion of each plot 7 or 8 years later. We measured herbaceous standing biomass and cover and soil variables (soil organic C, N, δ13C and δ15N) in unburned, transition-burned and maintenance-burned treatments. Greater δ13C at 10-20 (-17 ‰) than 0-10 (-20 ‰) cm depth increment confirmed that vegetation was historically mostly C4 grassland that ...