Patrick Williston

M.Sc. (1999)

Thesis Title:

Floristics and Successional Patterns of Microbiotic Crusts in Ponderosa Pine Forests of Southern Inland British Columbia

Funded in part by BC Ministry of Forests

Abstract:  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 and contains a key to common species.  Successional patterns are described for vascular plants, 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.  Early successional sites were often dominated by xerophytic crustose and squamulose lichens, 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 describes the floristics and successional patterns of microbiotic crusts; this is important for managing species diversity in one of British Columbia’s most restricted ecosystems.