Distribution of Corticolous Noncrustose Lichens on Trunks of Rocky Mountain Junipers in Boulder County, Colorado
Abstract
Nineteen species of noncrustose lichens were found on juniper bark. Of these, three species had relatively high cover and frequency values and were characterized as typical lichens of Rocky Mountain junipers: Xanthoria fallax, Phaeophyscia hirsuta and Physcia caesia. Total cover per tree was low (4%), and most species preferred the north and east sides of trunk bases. These distributional trends may reflect gradients of exposure to wind, insolation, and rate of bark exfo- liation. The trunk of a tree provides a wide spectrum of microhabitats for epiphytic vegetation. The physical and biotic factors that interact to create these environments have been dis- cussed in great detail by Barkman (1958). Horizontal and vertical gradients of light, water, and temperature depend upon direction of trunk exposure and height above ground. Bark hardness, texture, water-holding capacity, and acidity vary among tree species and within species according to age of the bark. In the Front Range area of Colorado, tree-host preferences and horizontal and vertical tree-trunk distributions of epiphytic lichens have been examined for riparian deciduous trees (Carmer 1975) and for Douglas fir and subalpine fir (Gough 1975), but not for Juniperus scopulorum Sarg., Rocky Mountain juniper, which is common in the open park-like stands of ponderosa pine found on south-facing slopes in the foothills. The objectives of this study were to identify the lichen species epiphytic on Rocky Mountain junipers and to measure their horizontal and vertical distributions on trunks.
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