Gradient Analysis of Vegetation Dominated by Two Subspecies of Big Sagebrush

Abstract

Stands of vegetation dominated by basin big sagebrush (Artemisia tridentata Nutt. subspecies tridentata) intergrade with stands dominated by Wyoming big sagebrush (A rtemisia tridentata Nutt. subspecies wyomingensis) on the Idaho National Engineering Laboratory in southeastern Idaho. Detrended correspondence analysis and correlation were used to elucidate potential relationships between vegetation patterns and soil factors along a gradient from stands having only the subspecies tridentata to stands having only the subspecies wyomingensis. Distributions of the subspecies were consistently associated with gradients in soil texture. Basin big sagebrush was most abundant on sandy soils and Wyoming big sagebrush was dominant on finer textured soils. Mixed stands occurred on central portions of the gradient. Similar results for 3 study areas were observed, despite differences in soil texture between areas. Thus, the distributional patterns are associated with changes in soil texture rather than actual amounts of sand, silt, or clay. Sagebrush shrublands of the Intermountain West and Great Basin regions are managed for a variety of uses, such as livestock grazing, wildlife habitat, and recreational activities. Because management practices often affect biotic and abiotic components of the environment, the relationships between various plant species on these shrublands and the environmental factors that the plants Authors are senior research assistant and professor, Department of Biological Sciences, Idaho State University, Pocatello 83209. Authors thank Dr. O.D. Markham for his support, N. Cole and D. Pavek for field assistance, D. Floyd and S. Strahm for computer assistance, M. Jensen for soil profile descriptions, and Dr. R. Nowak and two anonymous reviewers for reviewing the manuscript. This paper is a contribution from the Idaho National Engineering Laboratory Ecological Studies Program, supported by the Office of Health and Environmental Research, U.S. Department of Energy, contract no. DE-AS07-76ID01529. Manuscript accepted 7 August 1985. experience is of interest. The relationships between Artemisia species and environment have commanded particular attention. Distributions of various species of Artemisia are correlated with a variety of soil and climatic factors (e.g., Robertson et al. 1966, Fosberg and Horonaka 1964, Sabinske and Knight 1978, West et al. 1978). A study of sagebrush distribution at the Idaho National Engineering Laboratory (INEL) in southeastern Idaho (Shumar 1983) identified both pure and mixed stands of basin big sagebrush (Artemisia tridentata Nutt. subspecies tridentata; Beetle 1960) and Wyoming big sagebrush (Artemisia tridentata Nutt. subspecies wyomingensis; Beetle and Young 1965). (Pure refers to species assemblages containing one subspecies or the other but not both; mixed stands contain both subspecies.) The size of the basin big sagebrush stands was unexpected because previous reports suggested that the expansive lava flows and flats of the upper Snake River Plain were predominantly occupied by Wyoming big sagebrush (Harniss and West 1973, McBride et al. 1978) and contained of basin big sagebrush (Winward 1970). However, some of these basin big sagebrush patches on the INEL may be as large as 65 km2 (Shumar 1983). General descriptions of the soil properties associated with the distributions of basin big sagebrush and Wyoming big sagebrush occur in the literature. Basin big sagebrush occurs on deep (Beetle 1960, Hironaka 1978, Winward and Tisdale 1977), well-drained (Tisdale and Hironaka 1981), often sandy soils (Morris et al. 1976), in valley bottoms, on foothills, or along drainages. Its distribution often coincides with high water tables or deep moisture accumulations (Morris et al. 1976). Wyoming big sagebrush can be found on moderately deep to shallow soils (Hironaka 1978) of medium texture that often limit water penetration (Morris et al. 1976). These plants sometimes occur on immature soils (Morris et al. 156 JOURNAL OF RANGE MANAGEMENT 39(2), March 1986 This content downloaded from 207.46.13.66 on Sun, 12 Jun 2016 05:53:39 UTC All use subject to http://about.jstor.org/terms 1976) or slightly saline soils (Tisdale and Hironaka 1981). This subspecies is found on lower slopes of major drainages (Winward and Tisdale 1977) or on hilltops and flats (Beetle and Young 1965). Because of the extent of the pure and mixed stands of the 2 sagebrush subspecies on the INEL, and because of the generalized nature of the information on their relationships to environment, it seemed that an intensive study employing ordination procedures might provide insights into the factors affecting their distributions. The objective of this study was to generate hypotheses about relationships between the distributions of the sagebrush subspecies and characteristics of the soil using ordination and correlation analyses.