Post-fire recovery of desert bryophyte communities: effects of fires and propagule soil banks

摘要

Questions As changing wildfire regimes modify North American deserts, can fires of greater severity and frequency negatively impact the recovery of native bryophyte communities, which are not adapted to such disturbances? Does post-fire recovery result from the survival of existing surface plants, dormant propagules in sub-surface soil banks (dispersal in time) or aerial immigration into burned sites (dispersal in space)? Do wildfires negatively affect the survival of propagules in bryophyte soil banks? Location Continental arid shrublands, Mojave Desert, southwestern US. Methods We characterized bryophyte communities along a post-fire chronosequence spanning three decades across sites where fires had different severities, ages and potential fuels. Three community profiles (surface, soil and aerial) were surveyed with a combination of on-site surveys and emergence germination techniques. We tested for differences in beta diversity, species composition and richness with PERMDISP, PERMANOVA and linear mixed models, respectively. Results Burn severity was associated with differences in beta diversity, species composition and richness, while burn age was associated only with different composition and richness. No effect of potential fuel availability was found. More variation in composition was explained by significant differences among profiles than by other fire attributes. Species richness (but not beta diversity) was higher in soil profiles than in aerial spore rain or existing surface communities. Soils from the oldest and least severe burns had a greater number of species than soils from recent and more severe burns. Conclusions Bryophyte soil banks are common elements of desert soils that facilitate post-disturbance recovery of communities, but soil banks are themselves threatened by the intensifying frequency and severity of wildfires in North American deserts. Recovery of desert bryophyte communities seems to begin (but not necessarily conclude) within 30yr after wildfires. In the near future, communities may become perturbed from historical patterns as contemporary fire regimes undergo extensive changes.