Identifying practical, small-scale disturbance to restore habitat for an endangered annual forb

We sought to identify appropriate treatments to restore a small, urban patch of habitat for the endangered Clarkia franciscana (Presidio clarkia) in serpentine grassland. Goals included identifying effective and pragmatic treatments for introducing disturbance to the site and determining whether treatments used to establish Presidio clarkia would be appropriate in areas already occupied by this endangered serpentine endemic. This experiment tested fall burning, fall flaming, fall mowing with thatch reduction, fall scraping, fall tarping, spring burning, and spring mowing with and without thatch reduction. Half of all treated plots were seeded with clarkia. Clarkia density and vegetation composition were measured one and two years after treatment. Fall scraping, fall tarping, and fall flaming stood out as the most effective methods for increasing density. Fall scraping and fall flaming enhanced clarkia populations in unseeded plots where clarkia was initially present. In Year 1, these three treatments were also most successful in reducing annual grass cover and decreasing nonnative plant cover. Although other studies have shown spring treatments to be useful for reducing annual grass and thatch, and increasing native forbs, this study found that treating in late fall, after annual grasses had germinated, was critical for this site and not, as was previously presumed, harmful to the clarkia.