PONZETTI, JEANNE* AND BRUCE MCCUNE. Department of Botany and Plant Pathology, Cordley 2082, Oregon State University, Corvallis, OR 97331-2902. - Biotic soil crusts of the Columbia River Basin: landscape level variation in community composition.
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