The reintroduction of fire to Pacific Northwest prairies has been useful for removing non-native shrubs and supporting habitat for fire-adapted plant and animal species. However, very little is known about the influence of fire on prairie bryophyte and lichen communities. In this study, we investigated the effects of fire on ground-dwelling bryophytes and lichens by estimating standing biomass, cover, mat depth and functional group diversity in burned and unburned plots at five prairie sites located in the south Puget Sound bioregion of Washington State. After accounting for differences among sites, the bryophyte and lichen ground layer in burned plots had about 18% the biomass and about 60% the cover of unburned plots. All ground layer functional groups had lower average biomass in burned plots, except for ephemeral mosses, which had greater biomass. Forage lichens and nitrogen-fixing lichens were absent from all five burned plots. Of particular concern are the regionally rare, state-listed reindeer forage lichens (Cladonia ciliata var. ciliata, Cladonia ciliata var. tenuis and Cladonia portentosa ssp. pacifica), which occur at three of the five prairies we surveyed. Our results indicate that some lichen populations could be extirpated from these sites if they are not considered in prescribed burn management plans. We suggest some options that could maintain ground layer integrity while balancing other management objectives in the south Puget Sound prairies.