We examined biotic soil crust communities in the Horse Heaven Hills of Benton County, Washington, USA. Our study area consisted of over 5,000 acres of arid shrub-steppe habitat dominated by Pseudoroegneria spicata and Poa secunda, with scattered patches of Artemisia tridentata. We stratified the area into six topographic positions: ridges, toe slopes and benches, cool slopes, warm slopes, cool draws, and warm draws. We collected abundance data on species and morphological groups of terricolous lichens and bryophytes in 350 plots. Dominant species and morphological groups at this site include Tortula ruralis, short mosses group, Cladonia pocillum group, Diploschistes muscorum, Leptochidium albociliatum, Leptogium spp., and Trapeliopsis bisorediata sp. nov. We found that the biotic soil crusts communities varied by topographic position and previous soil disturbance. Warm draws and cool draws had the lowest crust cover and the fewest species. Crust cover and diversity were inversely related to cover of Bromus tectorum. In addition, community composition varied by aspect, slope, and soil chemistry. The biotic crust communities appeared resilient to historical fires known from the past 18 years. Overall, we found considerable variation in biotic soil crust communities within this study area. We recommend that land managers consider the landscape level variability in soil crusts when monitoring and assessing impacts to these organisms.

Key words: biotic soil crusts, bryophytes, composition, gradient analysis, lichens, shrub-steppe