Coyote Brush as Facilitator of Native California Plant Recovery in the Santa Monica Mountains

Abstract

Exotic annual grasses now cover large areas of southern California that were once stands of native California sage scrub (CSS), or a mixture of native grasses, forbs, and CSS. Both CSS and California grasslands are threatened habitats, where restorations of type-converted landscapes are often burdened by the persistent dominance of non-native annual grasses. Research finds that once exotic grasses take hold in these areas, native plant communities are extremely slow to recover, if they recover at all. Coyote brush (Baccharis pilularis DC) is a native shrub common to CSS habitat and often appears in a complex mosaic with other vegetation types including grasslands. Coyote brush has been documented invading grasslands, resulting in a change of state from grassland to shrubland in northern California. This study investigates the long-term consequences of coyote brush invasion in a type-converted landscape of southern California. Stands of expanding coyote brush were transected to identify species composition along a spatial and temporal continuum. Results show that, following initial invasion, non-native species are gradually replaced by, not only coyote brush, but also several other noteworthy native species. This study finds that over the 37 yr timeframe, exotic grasses gradually decline while native plant cover increases in landscapes invaded by coyote brush. We conclude that in the Santa Monica Mountain areas studied, coyote brush invasion of type-converted landscapes leads to increased native plant diversity that includes native grasses and a variety of shrubs.