A Comparative Study of Lichen and Bryophyte Communities on Sandstone and Ultramafic Bedrocks Along a Maritime Gradient in Central California

Aims Lichens and bryophytes are an often overlooked, yet dominant biotic component of rock outcrops and other lithic habitats. Saxicolous lichen and bryophyte communities are frequently species‐rich and play important ecological roles, including rock weathering, soil formation, and vascular plant recruitment. In this study, we test whether saxicolous communities differ between two substrate types along a coastal to inland spatial gradient. Location Ultramafic and sandstone rock outcrops in central California in San Luis Obispo, Monterey, and Kern counties. Methods We sampled saxicolous communities of eight ultramafic and eight sandstone outcrop sites along a 70 km maritime influence gradient using 20 × 20 cm quadrats stratified between north‐ and south‐facing rock aspects. For each quadrat, species composition, distance above the ground, and rock microtopography characteristics were recorded. For each site, rock elemental composition and climate parameters including rainfall, temperature, and fog were documented. Results We recorded 132 lichen and seven bryophyte taxa across 128 quadrats. Saxicolous communities were significantly different between ultramafic rock and sandstone, as well as between coastal, intermediate, and inland sites. Ultramafic rocks hosted fewer species overall but had a higher abundance and diversity of cyanolichens. The effect of rock type on species composition was mediated by maritime influence, with coastal samples showing greater cross‐substrate differentiation than intermediate and inland samples. Conclusions Our results demonstrate the interactive roles of substrate, climate, and microtopography in shaping saxicolous communities. The role of substrate in structuring saxicolous communities is mediated by climate and accentuated by the different microtopography profiles of the ultramafic and sandstone rocks. Improving our understanding of how saxicolous communities vary across the landscape is an important step in identifying conservation priorities for these highly diverse and ecologically significant communities.