California’s coastal sage scrub (CSS) habitats are among the most threatened habitats in the state’s Mediterranean regions, due to invasion by exotic annual vegetation in concert with anthropogenic disturbances. Bromus species are among the most abundant invasive annual grasses, and they appear to be able to dominate for long periods of time, interfering with CSS establishment. Restoring CSS involves both control of exotic annuals, and reintroduction of natives. We evaluated methods for reintroducing CSS species to a site dominated by Bromus diandrus (ripgut brome) for over 60 years, following prescribed burning or tillage (hereafter, management treatments). We compared CSS establishment between seeded, transplanted and no-revegetation (control) subplots, crossed with hand-weeding of Bromus across management treatments.
Results/Conclusions
CSS species had low seedbank representation, thus fewer species established in control compared to seeded and planted subplots. However, control subplots in managed treatments had greater recovery than in an unmanaged treatment. In each management treatment the addition of planted seedlings led to immediate increases in native richness, while in seeded subplots richness increased slowly over two growing seasons. Richness across management treatments declined after several more growing seasons due to competition between establishing natives. Native percent cover increased significantly and equally between planted and seeded areas over time. Hand-weeding significantly increased richness and cover across management treatments over time, but in few of these treatments individually. The timing of revegetation after Bromus management was critical: recovery was significantly less if revegetetation was delayed beyond the first post-burn growing season.