Interpretation of environmental gradients which influence sagebrush community distribution in northeastern Nevada

Abstract

Sagebrush stands on the Humboldt National Forest, northeastern Nevada, were classified by two-way indicator species analysis (TWINSPAN) into 15 community types. Detrended correspondence analysis (DECORANA) was used to ordinate samples and plant species and characterize environmental gradients regulating community structure. Regression of soil attributes with sample ordination scores suggested that the plant communities respond to a complex gradient involving soil depth, water holding capacity, mollic epipedon thickness, clay content, and effective rooting depth. Soil chemical properties which displayed significant correlations with sample ordinations included pH, base saturation, calcium, total nitrogen, organic matter, and phosphorus. These soil properties are considered to either directly influence or indirectly reflect the available soil moisture of a site. The transition from black sagebrush (Artemisia nova Nels.) to low sagebrush (A. arbuscula Nutt.), basin big sagebrush (A. tridentata Nutt. ssp. tridentata) and mountain big sagebrush (A. tridentata Nutt. ssp. vaseyana) stands along DECORANA Axis 1 appeared to represent a gradient of increasing available soil moisture. Elevation and aspect were not correlated with sample ordination scores. This lack of correspondence is presumably due to various soil properties (e.g., depth, rock content, texture) which modify the direct effects of elevation and aspect on available soil moisture.