The diverse lichen flora of the Pacific Northwest is being impacted by population growth and by forest management practices. Accumulating information about our lichen flora will improve our conservation strategies. This dissertation first collects information to improve our understanding of how lichen communities vary among forests of differing structure, and across the western Oregon landscape. It then proposes a method to predict species occurrence in unsampled sites by utilizing the information on forest characters and environmental gradients at sampled sites. Macrolichen communities sampled in coniferous forests revealed that old-growth stands (>200 yrs old) harbored communities that differed from those in young forests (50-110 yrs old). Even more atypical communities occurred in macrolichen hotspots, which were primarily in riparian zones. Many macrolichen species were associated with these hotspots, including numerous nitrogen-fixing cyanolichens. Macrolichen species associated with old-growth forested plots included the nitrogen-fixing lichen Lobaria oregana and several forage-providing alectorioid lichens. The presence of remnant old trees apparently increased the occurrence of old-growth associates in young stands. The calicioids, a group of microlichens investigated only in the Cascades, had a strong association with old growth forest and remnant trees. Diversity of calicioids may also be increased by legacy structures such as old snags and wolf trees. These structures increase continuity between current and previous stands. Macrolichen communities varied between the Coast and Cascade Mountain Ranges, following climatic gradients, particularly annual precipitation. Successional patterns in macrolichen communities appeared to differ between the mountain ranges. The modeling method proposed for using habitat associations to predict occurrence has several advantages over common modeling methods, such as regression. The method is simple, avoids parametric assumptions, provides easy updating of models as additional sites are sampled, and automatically accounts for interactions among predictor variables. It can be linked with GIS data and software to map estimated probability of occurrence across landscapes. The data on calicioids from the Cascades, supplemented with additional stand inventories, were used to test and demonstrate the modeling method. / Graduation date: 2001

Pendent Usnea species were collected in western Oregon and examined. Character states, such as cortex-medulla-axis ratio; fibril length; papilla diameter; branching patterns; and presence or absence of fibrils, papillae, soredia, isidia; plus chemistry, were recorded and analyzed by inspection for differences. Historical names were researched in the literature. A comparison was made between species concepts used in these accounts, with many conflicting concepts encountered. Selected morphological characters were examined by scanning electron microscope, or dissecting microscope, described, and illustrated. The characters reviewed included articulate fissures; isidia and soredia; cortex-medulla-axis ratio; papillae; and foveate pits. Species determinations were made for field collections. Names were found for all specimens inspected without introducing new names at this time. Eight pendent species were found in western Oregon; they are Usnea cavernosa, Usnea ceratina, Usnea fillpendula, Usnea hesperina subsp. liturata, Usnea inflata, Usnea leucosticta, Usnea longissima, and Usnea merrillii. A practical key to taxa with descriptions is provided and geographic distributions are recorded in tables and maps. / Graduation date: 1995