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.