WILLISTON, PATRICK S. Department of Botany, University of British Columbia Herbarium, #3529-6270 University Boulevard, Vancouver, B.C., Canada, V6T 1Z4. - Successional patterns of microbiotic crusts in ponderosa pine forests of southern inland British Columbia.
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
Key words: British Columbia, cryptogamic crust, microbiotic crust, ponderosa pine forests, positive feedback, succession