Great Basin Naturalist


Desert plants can influence the pattern of resources in soil resulting in small-scale enriched zones. Although conceptually simple, the shape, size, and orientation of these "resource islands" are difficult to study in detail using conventional sampling regimes. To demonstrate and alternative approach, we sampled soil under and around individual Artemisia tridentata (sagebrush), a dominant shrub of cool desert environments, and analyzed the samples with univariate statistics and geostatistics. Univariate statistics revealed that soil variables like total inorganic-N, soluble-C, and microbial biomass-C were distributed with highest mean values within about 25 cm of the plant axis and significantly lower mean values at distances beyond 60 cm. However, such simple analyses restricted our view of resource islands to identically sized, symmetrical accumulations of soil resources under each plant.

Geostatistics provided additional information about spatial characteristics of soil variables. Variography revealed that samples separated by a distance of less than about 70 cm were correlated spatially. Over 75% of the sample variance was attributable to spatial variability. We modeled these spatial relationships and used kriging to predict values for unsampled locations. Resulting maps indicated that magnitude, size, and spatial distribution of soil resource islands vary between individual plants and for different soil properties. Maps, together with cross-variography, further indicate that resource islands under A. tridentata are not always distinguishable from the surrounding soil by sharp transition boundaries and may be asymmetrically distributed around the plant axis.