Microbiotic crusts are an important component of the ecology and species diversity of terrestrial ecosystems in semiarid regions. This study documents 72 lichen species and 48 bryophyte species occurring in the ponderosa pine forests of southern inland British Columbia. Successional patterns are described for lichens and bryophytes along a disturbance gradient reflecting past grazing activity by livestock. While species richness among vascular plants varied little with disturbance, microbiotic species richness was found to differ significantly. Maximum richness occurred in moderately disturbed sites. Indicator species for early versus late successional sites were discerned using Principal Components Analysis. Xerophytic crustose and squamulose lichens often dominated early successional sites, while late successional sites also supported foliose lichens, fruticose lichens, and bryophytes. It is hypothesized that this trend from smaller to larger species relates to increased moisture retention, and denotes a positive feedback mechanism. This study contributes to our understanding of the ecology of one of British Columbia's most restricted ecosystems.

Key words: British Columbia, cryptogamic crust, microbiotic crust, ponderosa pine forests, positive feedback, succession