Responses of exotic plant species to fires in Pinus ponderosa forests in northern Arizona

Changes in disturbance due to fire regime in southwestern Pinus ponderosa f orests over the last century have led to dense forests that are threatened by widespread fire. It has been shown in other studies that a pulse of nati ve, early-seral opportunistic species typically follow such disturbance eve nts. With the growing importance of exotic plants in local flora, however, these exotics often fill this opportunistic role in recovery. We report the effects of fire severity on exotic plant species following three widesprea d fires of 1996 in northern Arizona P. ponderosa forests. Species richness and abundance of all vascular plant species, including exotics, were higher in burned than nearby unburned areas. Exotic species were far more importa nt, in terms of cover, where fire severity was highest. Species present aft er wildfires include those of the predisturbed forest and new species that could not be predicted from above-ground flora of nearby unburned forests.