Biotic soil crust lichen diversity and conservation in shrub-steppe habitats of Oregon and Washington

Biological soil crusts are ecosystem engineers in arid and semi-arid habitats; they affect soil chemistry, stability, and vegetation. Their ecosystem functions may vary depending on species composition; however, lichen species diversity is poorly known in the Pacific Northwestern drylands of North America. We sampled 59 random and 20 intuitive plots throughout central and eastern Oregon identifying 99 lichen taxa, 33 of which occurred in only one plot and seven of which were new to Oregon (Acarospora obpallens, A. terricola, Catapyrenium psoromoides, Placidium fingens, P. pilosellum, P. yoshimurae and Psora luridella). We compile records from herbaria and other studies to evaluate the rarity of observed species and potentially rare species known from nearby locations. We conclude that 37 species are likely rare or uncommon in our study area. Many of these appear to be associated with calcareous substrates. We model occurrences in relation to climate and soil variables for four uncommon lichen species: Acarospora schleicheri, Fuscopannaria cyanolepra, Rhizocarpon diploschistidina, and Texosporium sancti-jacobi. Based on climate and soil variables, we map regions of Oregon that may support new populations of these species and overlay habitats unsuitable for biotic crusts due to development and agriculture. These species, except Fuscopannaria cyanolepra, are strongly associated with the fine soils along the Columbia and Treasure Valleys that are most intensively used for agriculture. We anticipate that our summaries will further the understanding of lichen component of biological soil crust communities in eastern Oregon and suggest focal species for future conservation efforts.