WESTERN JUNIPER WOODLAND (61)

Geographic Distribution. Western juniper (Juniperus occidentalis) is a common foothills vegetation type for many of the mountain ranges of eastern Oregon. Juniper reaches its greatest extent in the High Lava Plains Ecoregion centered on Bend, Oregon.

Structure and Appearance. This woodland type is typified by its open canopy (less than 30% crown closure), single story, short stature (6-20 feet tall) trees. Understory vegetation in these stands tends to be dominated by sagebrush species, although introduced annual grasses and native bunchgrasses can be important depending on site history and disturbance. As site productivity conditions improve, or as soil moisture availability increases, the pure stands of juniper give way to mixed stands of juniper and ponderosa pine (Pinus ponderosa).

Composition. In most stands western juniper dominates the tree layer. The most frequently encountered shrubs in this cover type are sagebrush species. Big sagebrush (Artemisia tridentata) is the most common with rigid sagebrush (A. rigida) and low sagebrush (A. arbuscula) also commonly found. Other shrubs associated with this type are mountain mahogany (Cercocarpus ledifolius), bitterbrush (Purshia tridentata), and rabbitbrush (Chrysothamnus nauseous and C. viscidiflorus).

Grasses characterize the herbaceous layer. Cheatgrass (Bromus tectorum) and bottlebrush squirreltail (Sitanion hystrix) are typical and dominant on overgrazed or disturbed sites. Native bunchgrasses can usually be found. Idaho fescue (Festuca idahoensis), bluebunch wheatgrass (Agropyron spicatum), Thurber's needlegrass (Stipa thurberiana), and Sandberg's bluegrass (Poa secunda) are the most commonly encountered.

Landscape Setting. Western juniper occupies the transition zone between conifer dominant uplands and the shrub-steppe basins of eastern Oregon. In the driest mountain ranges of southeastern Oregon, i.e. the Trout Creek and Pueblo Mountains, juniper is found at all elevational ranges. Western juniper's range is increasing in Oregon. Overgrazing and fire suppression are considered to be the primary factors for the spread of this type.

References. Crawford and Chappell 1999, Dealy et al. 1981, Monzingo 1986, Kagan and Caicco 1991.