The vegetation in the ancient lake basin portion of Columbia Basin Province in Oregon is a natural shrub–grassland (10% or more canopy cover of shrubs) based on soil and ecological site studies made during the 1950s and 1960s.38
Shrubs, such as big sagebrush, rubber rabbitbrush, green rabbitbrush, and broom snakeweed are prominent throughout the lake basin area on deep sandy soils, on sandy soils overlying buried sedimentary deposits, and on shallow silty soils overlying the sedimentary lakeshore terrace. Broom snakeweed was called “matchweed” by local old-timers because sheepherders wintering flocks on this “desert range” would crumple a handful of the resinous shrub as tinder to start a warming fire.
The 1937 Western Range Survey of USDI Grazing Service District 7, which extended more or less from Arlington east to the Stanfield area and from the Columbia River south to about the present southern boundary of the Bombing Range, mapped extensive areas of bitterbrush. This federal grazing district was, at that time, used primarily to winter sheep and cattle. Subsequent soil and site studies reveal that bitterbrush grows in this area on relatively deep sands and on stabilized sand dunes. In this location and climate, bitterbrush does not grow on sites where the sandy surface soil overlying sedimentary deposits is relatively thin nor on sites where the surface soil is loamy or silty. This suggests that there is a soil–moisture relationship.
The presence of vigorous bitterbrush on sandy soils in this location under a climate of less than 9 inches annual precipitation, over 60% of which falls in winter, is indeed an ecological oddity given the normal habitat of bitterbrush in Oregon. Ecological site studies in Oregon over many years indicate that bitterbrush requires effective moisture of 12 inches annual precipitation or more. 5 In the case of this lake basin, some combination of ecological factors obviously is producing the required effective environment. Possible factors might include the region’s fog patterns and soil characteristics.
This basin is noted for dense fog in winter which might augment precipitation records significantly because plant foliage intercepts fog moisture and directs it into the soil profile. Actual annual precipitation may exceed 9 inches in some years.
Sandy soils characteristically absorb water readily; a high percentage of water absorbed is readily available to plants; and absorbed water penetrates deeper in sandy soil during a given period than in soils of finer texture.
Sandy soils actually retain water at depths for longer than one might expect because sand itself acts as a mulch that protects deep soil moisture from excessive evaporation and desiccation. Capillary movement of water upward is less among coarse soil particles than among fine soil particles. Early soil and site studies in this basin revealed moist to wet sand below about 6 feet deep in July and August. However, the possibility that the moisture was wicked up from an underground aquifer is not improbable in those days before irrigation from wells lowered the water table. Bitterbrush is a very deep-rooted plant once established, and it can utilize such deep soil moisture.
The water-holding capacity of various soil textures (Table 12) indicates that there is a greater increment in moisture equivalent (field capacity) between several sandy-soil textures than there is between loamy soils or soils of finer texture.19, 20
An interesting factor in soil–plant relationships is presented by the incremental increases in field capacity—such as the ability of the soil profile to retain water, from coarse sand to fine sand and likely on to loamy sand—and then the decreasing increment between loamy sand and sandy loam textures. The relationship between the incremental increase of field capacity in various sandy textures and the occurrence of bitterbrush in this sandy basin is not clear.
However, a cursory study of relationships between bitterbrush stands and soil textures in this sandy lake basin was made during the 1950s or 1960s.38 Auger holes at most section corners and quarter-corners provided a uniform grid sampling in an area about 4 miles from east to west and 2 miles from north to south. The area had sporadic stands of vigorous bitterbrush, some 30 to 40 sample plots. Essentially all plots with soil described as loamy sand or fine sand produced bitterbrush. In virtually all locations where soil was described as sandy loam there was no bitterbrush.
The phenomenon of loamy sand plots with no bitterbrush suggests a wildfire pattern. The major habitat for bitterbrush in this lake basin portion of Columbia Basin Province are the Quincy loamy fine sand and Koehler loamy sand soil series.
The growing season of bitterbrush in the lake basin is very much earlier than any other bitterbrush site in eastern Oregon. Here, bitterbrush flowers at least 30 days earlier than in other locations where it is common. That indicates the annual growth cycle of bitterbrush in the basin has adapted to begin and end while adequate soil moisture is available.
The herbaceous vegetation on these sandy sites is dominated by needle-and-thread, Indian ricegrass, Sandberg bluegrass, and varying amounts of Columbia milkvetch, wormwood, pteryxia, Gorman lomatium, and Carey balsamroot. Cheatgrass is a strong winter annual which forms rosettes 3 to 6 inches in diameter over the course of the winter and provides excellent spring forage for various classes of grazing animals. These sandy sites also are well known as nesting habitat for curlews.
The herbaceous vegetation on stabilized sand dunes is dominated by Indian ricegrass, yellow wildrye, Sandberg bluegrass, squirreltail, and a variety of perennial forbs such as buckwheat, Gorman lomatium, wormwood, pteryxia, scurfpea, yellow spiderflower, veiny dock, and pricklypear.
Around the southern perimeter of the lake basin, the natural plant community on the silty lake terrace site is one of the simplest natural plant communities in Oregon. It consists of a shrub–grassland in which big sagebrush, gray rabbitbrush, and broom snakeweed constitute slightly more than 10% canopy cover. Bluebunch wheatgrass and Sandberg bluegrass strongly dominate the total cover, and perennial forbs, such as yarrow, snow buckwheat, woollypod loco, and spreading phlox are sparse in the canopy cover. A good example of this site in reasonably natural ecological status is The Nature Conservancy’s Boardman Research Natural Area in the southeast corner of the Boardman Bombing Range.
Based on 171 recordings representing examples of eight major ecological sites in this province in southern Umatilla, Morrow, Gilliam, and Sherman counties on which native vegetation was in high ecological status, the natural vegetation of silty uplands in Columbia Basin Province in Oregon is a natural grassland, i.e., less than 10% canopy cover of shrubs (Fig. 16). Data from these 171 recordings show that low gray rabbitbrush was on 87% of the plots but in very minor amounts. In contrast, big sagebrush was recorded on only 29% of the plots and only in minor amounts. It is typical of the rangelands throughout the silty uplands of this province in Oregon to have low gray rabbitbrush and broom snakeweed, rather than big sagebrush, as the shrub component of native plant communities in deteriorated ecological status. Natural revegetation of abandoned croplands in this province results in gray rabbitbrush as the primary shrub component. Other shrubs that are sparse in examples of high-ecological-status plant communities include rose, gray horsebrush, and green rabbitbrush.
Figure 16: Managed natural upland grasslands in Columbia Basin Province, Oregon
Obviously, the question of fire arises in discussions of whether these plant communities are natural grasslands. Fire can temporarily eliminate big sagebrush and may even aggravate growth of gray rabbitbrush. However, the area represented by the recordings is extensive, so it is not reasonable to assume that all the examples of high ecological status had uniform and comparable fire histories and that an original sagebrush cover had been uniformly and permanently altered by fire over the entire area.
Based on ecological site studies, the natural shrub pattern on silty upland ranges in Columbia Basin Province of Oregon changes from east to west. East of the southwest corner of Morrow County, big sagebrush is minimal, if present at all, in native plant communities in high ecological status. Big sagebrush is not a prominent shrub even under deteriorated ecological status. However, in the vicinity of southeastern Gilliam County and west into southern Sherman and Wasco counties, the likelihood of big sagebrush increases somewhat, especially under deteriorated ecological status. Still, shrubs collectively usually do not make up 10% canopy cover on silty upland ranges in that portion of the Columbia Basin Province.
Several broad ecological factors are related to this phenomenon.
1. The reason big sagebrush is minimal, if present at all, east of Gilliam County may be that Blue Mountain Province native plant communities form a buffer zone between that portion of the Columbia Basin and the John Day Province to the south. Big sagebrush is a prominent component of the natural shrub–grasslands that typify the John Day Province. Blue Mountain native plant communities have evolved under very favorable soil and climate conditions, and a wide variety of other shrubs typify this province. For this reason, big sagebrush has not been able to encroach north through the vigorous Blue Mountain plant communities. This concept is supported by the fact that, throughout Blue Mountain Province, big sagebrush is not a prominent shrub no matter what the ecological status of the plant community.
2. West of Kinzua, the westernmost extent of Blue Mountain Province, a huge topographic saddle extends from Kinzua west about 50 miles to the Mutton Mountains in the northeast corner of Warm Springs Indian Reservation. The Deschutes and John Day rivers flow north through this saddle; however, the rivers’ tributaries generally are entirely within John Day or Columbia Basin province. The demarcation line between the two provinces essentially is the division between watersheds draining north into Columbia Basin from those draining south into John Day Province.
Along this huge saddle, the Columbia Basin and John Day provinces are contiguous at a relatively low elevation of 3,000 to 3,500 feet. Presumably, this offers less resistance to encroachment of vigorous shrubs, such as big sagebrush, from John Day Province into Columbia Basin Province, unlike the situation in the Blue Mountain buffer zone. Nevertheless, native plant communities in high ecological status on silty aeolian Columbia Basin sites, such as near Shaniko, generally do not support a 10% canopy cover of shrubs. This is in spite of the likelihood that native vegetation in the vicinity of Shaniko was decimated in early 1900s when Shaniko was the largest inland shipping center for wool in United States.
Two reasonable conclusions are that the natural native vegetation on upland silty aeolian soils of Columbia Basin Province in Oregon was not a shrub–grassland, and that big sagebrush is not a vigorous component of deteriorated plant communities, such as those in John Day Province.
Specimens of big sagebrush that look very old are in western Columbia Basin Province. They are almost exclusively along drainageway bottoms in the Deschutes and John Day river canyons and their tributaries. In this part of the province, these drainageway bottoms consist of deep, very gravelly and stony colluvial materials originating from nearby basalt rimrocks and canyon walls. These kinds of soils provide ideal sites for big sagebrush. In the same area, where silty alluvium from upland silty soils has accumulated as meadows in drainages, the natural vegetation consists of basin wildrye and associated meadow species, depending upon degree and duration of soil moisture.
It seems reasonable to assume that the incidence of big sagebrush in the western part of the province likely is related to the avenues for encroachment that have been provided over time by the Deschutes and John Day river canyons and their dendritic tributaries, which have suitably deep, coarse, colluvial soils.
In the Columbia Basin Province of Oregon, the silty upland ranges include a ecological site locally called scabland. It occurs along the outer edges of ridgetops and on sloping areas in minor drainages between about 1,000 and 3,500 feet elevation. Slopes vary from 2 to 20%. The soil of this site is very stony loam and is very shallow (7 to 10 inches) over basalt bedrock. Natural vegetation is dominated by Sandberg bluegrass and stiff sagebrush, i.e., a shrub–grassland. Some areas, however, have no stiff sagebrush although the soil and other components of the plant community remain the same.
Overall, the natural plant communities of silty upland sites throughout the Columbia Basin Province of Oregon consist primarily of bluebunch wheatgrass, Sandberg bluegrass, Idaho fescue, and a wide variety of perennial forbs. Idaho fescue is absent on the most droughty sites, such as south exposures, but it strongly dominates the plant community on more moist sites such as steep north exposures.
The cultivar ‘Sherman’ big bluegrass was originally selected from a grassland site near Moro in Sherman County. Beardless bluebunch wheatgrass, from which the cultivar ‘Whitmar’ was developed, has been recorded in the silty-soil site west of Boardman and north of the sandy-soil area. However, the type location from which Whitmar was selected is in Whitman County, Washington.