Journal of Arid Environments Journal of Arid Environments 61 (2005) 609–629 The influence of elevation, shrub species, and biological soil crust on fertile islands in the Mojave Desert, USA D.B. Thompson à , L.R. Walker, F.H. Landau, L.R. Stark Department of Biological Sciences, University of Nevada, P.O. Box 454004, Las Vegas, Nevada 89154-4004, USA Received 10 March 2004; received in revised form 27 September 2004; accepted 29 September 2004 Available online 9 December 2004 Abstract We quantified soil nutrients and biological crust cover (bryophytes and lichens) under the canopies of three species of Mojave Desert shrubs and in interspaces between shrubs at three elevations to determine the effects of shrub species, soil crust, and elevation on islands of soil fertility. Means of pH, organic matter, total Kjeldahl nitrogen, nitrogen mineralization, and gravimetric soil moisture are significantly greater in soils under Ambrosia dumosa (Gray) Payne, Larrea tridentata Cov., and Coleogyne ramosissima Torr. than soils from adjacent interspace microhabitats. Although soil moisture and soil organic matter increase by a factor of 1.5 from the low elevation to the high elevation site, the ratio of shrub to interspace concentrations, or the difference in mean soil variables between shrubs and interspaces, is effectively constant and independent of elevation. Total bryophyte and lichen cover is relatively low (24.5%), however, there are 11 species of bryophytes and two species of lichens distributed across three elevations with the highest species richness and cover at the low-elevation site. Bryophyte and lichen cover is correlated with silt but is not related, consistently, to soil nutrients. Overall, the balance of processes controlling spatial aggregation of soil nutrients under shrubs is remarkably insensitive to potential differences in organic inputs among elevations, shrub species, and soil crust surfaces. r 2004 Elsevier Ltd. All rights reserved. Keywords: Ambrosia dumosa; Coleogyne ramosissima; Soil crust; Elevational gradient; Larrea tridentata; Soil fertility ARTICLE IN PRESS www.elsevier.com/locate/jnlabr/yjare 0140-1963/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2004.09.013 à Corresponding author. Tel.: +17028953269; fax: +17028953956. E-mail address: dthompsn@ccmail.nevada.edu (D.B. Thompson).