Because our study plots span a gradient in abundance of exotic plants, we are able to examine changes in populations of native plants across this gradient before and after fire. The exotic herbs on our study plots, common throughout the range of coastal sage scrub, are well suited to exploit the open ground uncovered by fire or other disturbances. Thus they are expected to return rapidly to their previous abundance or even increase after a fire. Exotic plants, in large numbers, could compete with the resprouting shrubs or seedlings of native plants, as well as with the native herbs that generally flourish following fire, inhibiting native plants’ recovery. Our study will evaluate how quickly exotics return to or increase their former abundance after fire and how this change interacts with native plants’ recovery over time.
Since spring 2002, each plot has been sampled annually. On each plot we established four permanent belt transects of 50 m × 1 m, between and parallel to the trap lines for rodents. During each vegetation survey we (a) count plant species richness within each belt transect; (b) estimate plant cover and height along each transect, using a point-intercept sampling method; and (c) estimate shrub densities (unburned shrubs, resprouting shrubs, and seedlings) within 12 quadrats measuring 1 m2 each along each transect. Within each 1-m2 quadrat we also visually estimate the percentage covered by exotic and native plants and count plant species richness.