A Relict Area in the Central Oregon Juniper Zone

Abstract

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.

Roadless Habitats as Refuges for Native Grasslands: Interactions With Soil, Aspect, and Grazing

“…It was surprising to find such clear evidence for the importance of distance from roads given the 200-yr history and severity of invasion in the grasslands of the California floristic province (Mooney et al 1986, Murphy and Ehrlich 1989, Heady 1995, Gerlach et al 1998. Although it is premature to say whether our results are likely to be general, we speculate that the effects of distance from roads may be even more pronounced in less thoroughly invaded landscapes, such as remote grasslands and shrublands of the Colorado Plateau and Great Basin (Driscol 1964, Kindschy 1994J. L. Gelbard, personal observation).…”

Persistence of Idaho Fescue on Degraded Sagebrush-Steppe

“…Site descriptions are summarized in Tables 1 and Defchutes Co. 2 and Figure 2. As far as is known, the Island has been grazed only by sheep for 2 successive summers during the 1920s (Driscoll 1964). Collected seeds were mechanically threshed and a seed blower was used to sort filled seeds from chaff and unfilled seeds.…”

“…Idaho fescue (Festuca idahoensisElmer), a native perennial bunchgrass, persists on degraded central Oregon sagebrush-steppe despite invasion by cheatgrass(Mack 1981), increased tree and shrub density from fire suppression Wigand 1994, Burkhardt andTisdale 1976), and overgrazing by livestock since the late 1800's(Galbraith and Anderson 1971, Strong 1940). Long-term grazing and alien invasion have extirpated some populations of Idaho fescue from similar sites in central Oregon(Driscoll 1964). Persistence of Idaho fescue on degraded sites may be explained by ecotypic differentiation, because introductions of cheatgrass and domestic livestock changed selective pressures importante que celle de l'espece introduite.…”

Western Juniper Expansion on Adjacent Disturbed and Near-Relict Sites

“…Grazing is not allowed, fire suppression is not active, and the plateau is controlled by Oregon State Parks personnel with usage limited to scientific and educational activities. The area has not been grazed for over 70 years, and the only historical account of livestock grazing was for sheep during 2 consecutive summers sometime between 1922 and 1928 (Driscoll 1964).…”