A Relict Area in the Central Oregon Juniper Zone

Vegetational and soil characteristics of two relatively undisturbed associations on a semi—isolated plateau in the central Oregon juniper zone were studied and related. Agropyrom spicatum was the most abundant herbaceous perennial in both entities. Artemisia tridentata was specific to the Juniperus/Artemisia/Agropyron association. Purshia tridentata was specific to the Juniperus/purshia/Agropyron association. The specificity of these species was related to the way soil characteristics affected the soil water regime and rooting resistance. Purshia tridentata occurred on coarse—textured stony soils overlying cracked bedrock. Artemisia tridentata occurred on finer textured nonstony soils with dense, clayey subsoils. Other differences in floristics, soils, and soil—factor effects between the two units were sufficiently great to warrant classification of the entities as individual ecosystems. The annual Bromus tectorum was a conspicuous part of the vegetational of both units. Juniperus occidentialis was not abundant in either association. It occurred in small clumps or as individual trees unevenly distributed throughout the area. Wildfires appeared to have been a major factor controlling the distribution of the species.