The Effects of Fire on California Sage Scrub Germination Assemblages

California sage scrub is an endangered, shrub-dominated, southern California ecosystem threatened by increasing fire frequencies and type-conversion to non-native grasslands. Once non-native grasses become established, their presence promotes more frequent fires, perpetuating grass dominance. To better understand how fire influences soil seed bank assemblages, we examined soil seed banks in burned and adjacent unburned sage scrub at the Robert J. Bernard Field Station (BFS) in two areas that burned in September 2013 and May 2017. In contrast to a previous soil seed bank study in California sage scrub, we found that unburned soil seed banks in sage scrub at the BFS were primarily composed of native seeds (88% of sprouts in unburned areas were native), highlighting that soil seed bank dynamics differ among California sage scrub sites. Despite burned areas supporting elevated densities of non-native seeds (the majority of which included Festuca myuros, a non-native grass), soil seed banks in our burned areas retained native seeds (21% of sprouts in burned areas were native), including native shrub species, suggesting that not all sage scrub habitats are primed to transition to non-native grasslands following disturbances. However, elevated densities on non-native seedlings in burned areas highlight the vulnerability of sage scrub to fire disturbances and the subsequent establishment of non-native grasses.