The Dalles Ecological Province

 

 
 
 

Location

The Dalles Ecological Province in north-central Oregon lies along the lower eastern slopes of the Cascade Mountains generally between about 2,000 and 4,000 feet elevation in the northern part and between about 2,500 and 4,500 feet elevation farther south, on the Warm Springs Indian Reservation. The province is relatively narrow, varying from about 6 to 15 miles wide east to west, and extends about 100 miles north to south.

This strip of country lying parallel to the Cascade Mountains is an area in which the hot, dry eastern Oregon summer climate significantly affects the ecology along the east slopes of the Cascades. It constitutes the transition between normal grasslands of Columbia Basin Province and Douglas-fir–hemlock forests of Cascade Province (Fig. 42).

Figure 42: A mosaic of natural grasslands and stands of deciduous and coniferous trees typifies The Dalles Province, Oregon

In Oregon, the province covers about 530,000 acres mainly in Wasco and Jefferson counties with a small proportion in Hood River County and a very small proportion in Deschutes County near Black Butte. The province extends north across the Columbia River into Washington.

In Oregon, The Dalles city is in the extreme northeast corner of the province. Mosier is in the northwest corner. Friend, Wamic, Pine Grove, and Simnasho are just inside the eastern boundary; there are no towns in the southern part of the province.

 
 

Description

Physiographically, The Dalles Province in Oregon consists mainly of east-sloping foothills and mountain slopes bisected west to east by numerous drainages, many having abrupt basalt cliff canyons originating in the Cascades and draining into Deschutes and Columbia rivers. Elevations range from about 100 feet along the Columbia River between Mosier and The Dalles to 5,110 feet on the north end of Green Ridge near Metolius River in the southern portion of the province.

 
 

Soils

Soils typifying The Dalles Province in Oregon have developed in a variety of parent materials related to the geology of the eastern slopes of Mt. Hood and the Cascade Mountains. Included are aeolian silts and volcanic ash, andesitic, basaltic, and sedimentary colluviums, and glacial outwash. Some small areas of alluvial soils lie along stream channels.

The major cultivated area in the province in Oregon lies south and west of The Dalles city. The soils are Chenoweth and Cherryhill loams and silt loams formed in old alluvium and consolidated colluvium on undulating 1 to 50% slopes. At one time much of this area was in orchards.

From The Dalles city south to about Wamic along the eastern portion of the province is a sloping plateau dissected from west to east by numerous drainages, many basalt rimmed. Some small areas in the plateau have been dry farmed for cereal grains. Soil series typifying this plateau are Ortley and Wamic which are formed in aeolian silts and volcanic ash overlying basalt bedrock.

Noncultivated soils can be grouped according to the natural vegetation produced: upland natural grasslands; bottomland natural grasslands; Oregon white oak; mixed ponderosa pine/oak; pine/bunchgrass; mixed ponderosa pine/Douglas-fir; and Douglas-fir/grand fir forest.

Soils associated with upland natural grasslands are on steep south-facing slopes along major drainages in the low-elevation northeastern part of the province. These soils are shallow cobbly loam with 45 to 75% slopes. A major soil series is Bodell, which is formed in basaltic colluvium over basalt bedrock.

Soils associated with bottomland natural grasslands are limited to certain reaches in major drainages. These alluvial soils are nearly level, deep sandy loams derived from an aggregation of upstream parent materials. A major bottomland soil series is Tygh.

Soils associated with nearly pure stands of white oak are mainly in the northern part of the province on steep south-facing slopes in higher, more moist elevations than where upland natural grasslands occur on similar topography. These soils are shallow to moderately deep cobbly loam with 35 to 65% slopes. Soil series include steep phases of Wamic, Skyline, and Hesslan, which are formed in a mix of aeolian and colluvium materials over basalt or sedimentary bedrock.

Soils associated with stands of mixed oak and ponderosa pine are mainly in the northern and eastern parts of the province at mid-elevations on plateaus and steep south-facing slopes. On some plateaus, the soils are in a complex soil pattern of nonstony mounds interspersed with very shallow stony soils, a pattern called biscuit scabland. Oak and pine grow on the biscuits which are typified by Ortley, Wamic, and Skyline soil series; they are derived from aeolian materials overlying basalt or sedimentary bedrock. The interspersed scabland is Bakeoven series which, in this province in Oregon, atypically does not produce a low-growing species of sagebrush. For one explanation of the origin of this patterned land, refer to the section on Columbia Basin Ecological Province in which biscuit scabland is a prominent, widespread phenomenon.

On other plateaus, mixed oak and pine grow on relatively level soils having deep, medium-texture surface layers and loamy subsoils. A representative soil series is Wamic, which is formed in aeolian materials over basalt bedrock.

In more moist, higher elevations, mixed oak and pine are on steep (45 to 75%) south-facing slopes of soils that are moderately deep cobbly or stony loams. A representative series is Bald, which is formed in aeolian materials and basalt colluvium overlying basalt bedrock.

Soils associated with ponderosa pine and bunchgrass plant communities lie mainly in the south half of the province, on the Warm Springs Indian Reservation. These soils include Booten and Shiva, which are sandy loams formed in basalt colluvium; Tenwater, Milldam, and Tolius, which are very cobbly silt loams formed in glacial outwash; and Hehe and Teewee, which are very stony loams formed in basalt colluvium.

Soils associated with ponderosa pine and Douglas-fir forests are in higher footslopes throughout the length of the province in Oregon. In the north, these soils include Bald, Wamic, Ketchly, and Frailey, which are formed in aeolian materials and colluviums over bedrock. Farther south on the reservation, these soils include series such as Smiling, Simnasho, and Pipp, which are strong sandy loams formed in colluvium of igneous rock and ash.

Soils associated with Douglas-fir and grand fir forests, which are mainly on north exposures at higher elevations in the northern part of the province in Oregon, are typified by such soils series as Bins and Fouts. These soils are formed in aeolian materials and basaltic and andesitic colluviums over bedrock.

 
 

Climate

Based on six official weather stations in the eastern low-elevation portion of The Dalles Province in Oregon, average annual precipitation in this area is about 14.5 inches of which about 25% occurs during the herbaceous native-plant growing season, March through June. October through February (winter) precipitation is about 66% of total annual precipitation. Average January maximum and minimum temperatures for this portion of the province are 38.7 and 22.6°F, respectively. Average March through June maximum and minimum temperatures are 65.5 and 36.5°F, respectively.

A precipitation map53 shows about 50 inches or more annual precipitation along the western boundary of The Dalles Province in Oregon. Temperatures at about 4,000 feet elevation, which is the western boundary of the province in Oregon, are not represented in data from official weather stations.

Along the province’s eastern boundary in Oregon, precipitation increases from east to west as elevation increases. The southernmost weather station, Montgomery Ranch south of Metolius River in Jefferson County, is both drier and warmer than stations farther north. This correlates with the previously described phenomenon of the advent of western hemlock at increasing elevations from north to south along the Cascade Mountains in Oregon.

 
 

Vegetation

According to the 1936 State of Oregon Forest Type Map54 which predates extensive logging, about 85% of The Dalles Province in Oregon was covered by coniferous and mixed coniferous and oak forest. About 5% was covered by Oregon white oak savannah, and about 10% was nonforested, conceivably natural grasslands (less than 10% canopy cover of shrubs). According to this map, ponderosa pine was by far the dominant tree species in the province. Based on field ecological studies, other coniferous tree species include Douglas-fir, grand fir, western white pine, lodgepole pine, western larch, and western red cedar, depending on the effective environment of the particular site.

Natural grasslands in The Dalles Province in Oregon are primarily on arid south-facing slopes in lower elevations along the northeastern portion of the province. Dominant species include bluebunch wheatgrass, Sandberg bluegrass, Idaho fescue, prairie junegrass, Lemmon needlegrass, and a wide variety of perennial forbs such as arrowleaf balsamroot, barestem and heartleaf buckwheats, carrotleaf and barestem lomatiums, yarrow, and lupine.

Sagebrush is not a component of upland plant communities in The Dalles Province even under deteriorated conditions. This includes very shallow, very stony scablands which normally grow low or rigid sagebrush in other provinces. However, sagebrush has encroached on some deteriorated bottomland sites. Gray rabbitbrush, gray horsebrush, and poison-oak grow in minor amounts on upland grassland sites.

Oak savannahs are primarily on south-facing slopes ranging from about 1,200 to 3,500 feet elevation and on steep north-facing slopes from about 1,000 to 3,000 feet elevation in the northeastern part of the province in Oregon. On south-facing slopes, the stand of oak is sparse; however, it dominates the aspect of the site. The understory is strongly dominated by bluebunch wheatgrass, Sandberg bluegrass, and Idaho fescue. A variety of perennial forbs and a few shrubs and oak reproduction are common. On steep north-facing slopes, oak grows with good stand density. Occasionally there are ponderosa pine and Douglas-fir. Idaho fescue, bluebunch wheatgrass, Sandberg bluegrass, and big and Kentucky bluegrasses are prominent. A wide variety of perennial forbs and such shrubs as bitterbrush, deerbrush ceanothus, serviceberry, snowberry, rose, gray rabbitbrush, and both oak and sparse pine reproduction are common.

The most arid portion of coniferous forest in The Dalles Province in Oregon is in stands of mixed ponderosa pine and Oregon white oak which are on ridgetops and sloping areas ranging from about 1,000 to 2,500 feet elevation. The overstory consists of ponderosa pine and oak; all age classes of both species are represented. A wide variety of perennial bunchgrasses and forbs constitute the understory along with abundant bitterbrush, deerbrush ceanothus, rose, serviceberry, snowberry, poison-oak, greenleaf manzanita, and both oak and pine reproduction.

As the effective environment improves due to increased elevation and/or increased moisture, conifer forest areas of The Dalles Province in Oregon are characterized by different plant communities; for example, ponderosa pine/bitterbrush/bunchgrass sites; ponderosa pine/Douglas-fir/mixed shrubs/elk sedge sites; mixed fir/ponderosa pine forest sites; and mixed fir forest sites.

Ponderosa pine/bitterbrush/bunchgrass sites occur from about 1,700 to 2,700 feet elevation. The shrub understory is dominated by bitterbrush. Dominant grasses include Idaho fescue and bluebunch wheatgrass.

Pine/Douglas-fir/mixed shrubs/elk sedge sites lie from about 1,200 to 3,000 feet elevation. The herbaceous understory typically consists of a wide variety of perennial species such as elk sedge, Idaho and western fescues, spike trisetum, Alaska oniongrass, Kentucky and pine bluegrasses, blue wildrye, pinegrass, and mountain brome. The forb component consists of such species as peavine, American vetch, woollyweed, cinquefoil, shiny frasera, Douglas deervetch, white hawkweed, licoriceroot, lupine, penstemon, strawberry, yarrow, big deervetch, mountain sweetroot, and arrowleaf balsamroot. The shrub component is also typified by numerous species in abundance. It commonly includes species such as bitterbrush; redstem, deerbrush and squawcarpet ceanothus; mockorange; blue elderberry; serviceberry; pipsissewa; oceanspray; greenleaf and pinemat manzanita; shinyleaf spirea; low Oregon-grape; rose; snowberry; and hazel. Ponderosa pine, Douglas-fir, incense-cedar, and white oak of all age classes may be in the stand.

The mixed fir–pine forest grows from about 2,500 to about 2,800 feet elevation on north-facing slopes and sloping areas. It has a relatively dense tree canopy cover which may include minor amounts of grand fir. The midstory consists of about 25% canopy cover of tall shrubs such as willow, thimbleberry, rose, blue elderberry, serviceberry, redstem and deerbrush ceanothus, mockorange, Cascade Oregon-grape, hazel, ninebark, trailing blackberry, oceanspray, snowberry, pinemat manzanita, pipsissewa, and birchleaf spirea. Both grasses and forbs constitute a sparse stand of shade-tolerant species such as pinegrass, elk sedge, blue wildrye, Kentucky bluegrass, false-solomonseal, woollyweed, and strawberry.

The mixed-fir forest is on mountain slopes ranging from about 2,500 to 4,000 feet elevation. It is primarily a Douglas-fir–grand fir forest which may have an occasional ponderosa pine, western larch, or western white pine in the stand. The understory is very sparse and consists of shade-tolerant species. The herbaceous understory is typified by Alaska oniongrass, elk sedge, blue wildrye, western fescue, mountain brome, tall trisetum, white hawkweed, peavine, strawberry, sword fern, arnica, mountain sweetroot, trillium, bunchberry dogwood, meadowrue, solomonplume, phantom-orchid, cleavers bedstraw, sandwort, pathfinder, and starflower. The shrub understory is typified by willow, vine maple, serviceberry, redstem ceanothus, snowberry, rose, hazel, honeysuckle, oceanspray, thimbleberry, bittercherry, trailing blackberry, golden (bush form) chinkapin, pipsissewa, greenleaf manzanita, Cascade Oregon-grape, twinflower, and reproduction of both Douglas-fir and grand fir.

The Dalles Province in Oregon is noteworthy for its wide variety of shrub, grass, and forb species and their abundance under tree canopies.

 

 
 

Management Implications

A very large portion of The Dalles Province in Oregon is forest and rangeland. An area of Chenoweth and Cherryhill soils south and west of The Dalles city was at one time used for orchards. Some areas of Wamic and Ortley soils are used primarily for dryland farming for cereal grain. All these soils are subject to soil erosion during storm seasons and spring runoff.

The southern half of the province in Oregon lies in the Warm Springs Indian Reservation and in Deschutes National Forest. Much of the north half in Oregon lies in Mt. Hood National Forest. Only about 25% of the province in Oregon is privately owned.

 
 

Province Demarcation

The Dalles and Columbia Basin Demarcation

The line of demarcation between The Dalles Province and Columbia Basin Province in Oregon starts in the northeast corner of The Dalles Province on the Columbia River east of The Dalles city near the mouth of Fifteenmile Creek and The Dalles dam. From there, the line travels south about 2 miles east of The Dalles city and continues south to west of Dufur, which is in Columbia Basin Province. The line continues south to a point just east of Friend, which is in The Dalles Province, and to a point east of Wamic which also is, barely, in The Dalles Province. From Wamic, the line wanders southwest to near Smock Prairie and then south to Pine Grove on Highway 216. From Pine Grove the line goes southeast to the pass on the ridge where the Wapinitia–Warm Springs road crosses the major ridge going south, the top of the Mutton Mountains.

At this ridgetop crossing, Columbia Basin, The Dalles, and John Day provinces join.

The demarcation line between The Dalles and Columbia Basin provinces in Oregon is based on soil lines between Frailey, Wamic, and Skyline soils, which typify the eastern footslopes of Cascade Mountains—The Dalles Province—and Condon, Walla Walla, Wapinitia, and Maupin soil series, which typify Columbia Basin Province.86

The Dalles and John Day Demarcation

At the ridgetop where the Wapinitia–Warm Springs road crosses the major ridge going south, the line of demarcation between The Dalles and John Day provinces winds south to the vicinity of Simnasho, which is in The Dalles Province. The line circles around Simnasho to the east and south and then head west toward Hehe Butte, also in The Dalles Province. From Hehe Butte the line travels south at about 2,500 feet elevation passing near Sawmill Butte, across the headwaters of Tenino Creek, and then southwest to Metolius River. The line follows Metolius River downstream to Fly Creek and then up Fly Creek and around the east side of Squaw Back Ridge at about 2,500 feet elevation to what is locally called Lower Desert. It is at this location that The Dalles, John Day, and Mazama provinces join.

The line of demarcation between The Dalles and John Day Provinces is based on soil lines between soil series such as Smiling, Hehe, Simnasho, and Pipp, which typify The Dalles Province, and soil series such as Simas, Watama, Prill, Mutton, and Madras, which typify John Day Province on the Warm Springs Indian Reservation.96

The Dalles and Mazama Demarcation

From the location near Lower Desert, the line of demarcation between The Dalles and Mazama provinces goes south and west to encompass a small area in Deschutes County that is southeast of Black Butte, which is in Mazama Province.

From the east side of Black Butte, the line goes northerly along Green Ridge at about 4,500 feet elevation to about where Abbot Creek joins Metolius River. It is at this location that The Dalles, Mazama, and Cascade provinces join.

The line of demarcation between The Dalles and Mazama provinces is a relatively short distance of about 35 miles. The line is based on soil lines between soil series such as Hehe, Teewee, Smiling, and Pipp, which typify The Dalles Province on the Warm Springs Indian Reservation, and soil series such as Deschutes and Shanahan, which represent the pumice mantle that typifies Mazama Province lying to the south of the reservation.70, 96

The Dalles and Cascade Demarcation

From the point that The Dalles, Mazama, and Cascade provinces join, the line of demarcation between The Dalles and Cascade provinces in Oregon meanders northward along the mountains at about 4,500 feet elevation. This line is at the approximate elevation at which western hemlock becomes a component of forested plant communities in this area. The advent of western hemlock signifies the location on the upper Cascade footslopes and mountain sides where the hot, dry summer climate of eastern Oregon is no longer an ecological factor influencing forest composition. Below this line, the forest is typified by ponderosa pine, Douglas-fir, and Oregon oak; above the line, the forest is typified by Douglas-fir, true firs, and hemlocks.

Numerous field observations over several decades are that the advent of western hemlock in the forest composition is a reliable widespread ecological indicator of the location on the landscape at which a very significant ecological change occurs when transecting from arid and warm forest to moist and cold forest. Other species—trees, shrubs, and herbaceous—also change from zone to zone in transecting dry–warm to moist–cold conditions. However, western hemlock was chosen as the key indicator species to differentiate between some ecological provinces in western Oregon because, first, it is widespread at higher elevations on both east and west slopes of the Cascades and from the Coast Range west to the Pacific Ocean; and, second, being a tree, it reliably indicates average climatic conditions that have prevailed over long cycles.

Elevations cited as western hemlock’s entry level in the forested plant community are based on observations of sites representing the climatic climax, i.e., on relatively level topography not significantly influenced by topographic exposure and where the plant community and soils likely are in equilibrium with long-term climatic conditions. Obviously, western hemlock cited as occurring at about 4,000 feet elevation in a climatic climax location will be at somewhat higher elevations on more arid south-facing slopes and at somewhat lower elevations on more moist north-facing slopes because of the influence of topographic exposure.

In the southern part of Wasco County, the line of demarcation between The Dalles and Cascade provinces, which is based on the appearance of western hemlock, drops to about 4,000 feet as it goes north. Western hemlock’s occurring at lower elevations in northern parts of Oregon than in southern parts is true for both eastern and western slopes of the Cascade Mountains as well as along the eastern slopes of the Coast Range. Apparently, this is due to the overall warmer climatic conditions to the south, which causes western hemlock to first appear at a higher elevation on mountain ranges.

The line of demarcation between The Dalles and Cascade provinces runs north to a point near the southeast corner of the upper Hood River Valley. It is at this point that The Dalles, Cascade, and Willamette provinces join.

Although the line between The Dalles and Cascade provinces is based on the elevational at which western hemlock appears, the line also is indicated by the general occurrence of such forested soils as Smiling, Simnasho, and Pipp, which typify The Dalles Province, and Howash and Mackatie forested soils, which typify Cascade Province on the Warm Springs Indian Reservation.96 Farther north, the line of demarcation is indicated by the general occurrence of such forested soils as Bald, Ketchly, and Frailey, which typify The Dalles Province in Oregon, and Divers, Hutson, and Thader forested soils, which typify Cascade Province in Oregon.89

The Dalles and Willamette Demarcation

The line of demarcation between The Dalles and Willamette provinces in Oregon goes north from near the southeast part of upper Hood River Valley at about 4,000 feet elevation. It runs along the ridge east of the valley and winds around the head of Neal Creek and north down the ridge nearly to Highway I-84 along the Columbia River. Here it veers sharply upriver nearly to Mosier, which is in The Dalles Province. The town of Hood River and the entire Hood River Valley are in Willamette Province.

The line of demarcation between The Dalles and Willamette provinces in Oregon is based on soil lines between Bald, Bodell, Frailey, and Ketchly soil series which typify The Dalles Province in Oregon, and Hood, Van Horn, Oak Grove, and Bins soil series, which typify Willamette Province in Oregon.89