Native plants in most California ecosystems are adapted to fire, but altered fire regimes and disturbance from firefighting activity, such as the construction of firebreaks or firelines, can change plant community composition and the ratio of native to nonnative species. In October 2007, a wildfire burned 710 acres through a chaparral/grassland mosaic on an ecological reserve, providing an opportunity to quantify fire and fireline disturbance impacts on native and nonnative species under differing disturbance conditions. In the spring of 2012 we sampled the plant community in three adjacent sites, focusing on Centaurea melitensis, which is a common nonnative invader after fire in California chaparral. The first site was burned and bulldozed, the second site was burned but not bulldozed, and the third site was not burned or bulldozed. The first site had also been sampled in the spring of 2008. After four years within the burned fireline site, the mean relative cover of C. melitensis decreased from 72% to 28%, but its density increased, and there were increases in the covers of nonnative annual grasses, litter, and native plants. Among the three sites in 2012, both of the burned sites had higher density and cover of C. melitensis and lower relative cover of annual grasses than the unburned site. The only site with notable native perennial presence was the burned fireline. The results of our study suggest that the recruitment of C. melitensis and some native species is promoted by fire. In the absence of additional disturbance by firelines, persistence of these taxa is limited by competition from nonnative annual grasses.
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Vol. 60 • No. 3