Vegetation responses to wildfire in native versus exotic Arizona grassland

Grass and herb cover, and woody plant densities were measured on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. At least 40 yr previously, the exotic plots had been seeded with two species of lovegrasses (Eragrostis spp.) native to southern Africa. A 1987 wildfire burned 11 native and 11 exotic plots. The fire reduced cover of both native and African grasses for two post‐fire growing seasons. Herb cover as a whole increased after the fire for 2 yr, although there were important differences among species. One of two dominant shrubs (Haplopappus tenuisectus) was killed by the fire, while the other (Baccharis pteronioides) was little affected. Mesquite trees (Prosopis juliflora) were killed to the ground by the fire, but 62 of 66 trees had re‐sprouted to an average 48% of pre‐burn height by 1990. Native and exotic grasses appeared equally tolerant of fire, probably because both evolved in fire‐type ecosystems. There was no evidence that fire can be used to permanently restore the diverse native flora to species‐poor plantations of the South African exotics.