PONDEROSA PINE-OREGON WHITE OAK FOREST (57)

Geographic Distribution. A low elevation forest found on the eastern flanks of Mount Hood and into the Columbia River Gorge. The type extends south to the Mutton Mountains of Wasco County. This type is also found in the foothills vegetation of southwestern Oregon, especially in the Rogue River Valley around White City.

Structure and Appearance. Open to closed canopy forest with small stature ponderosa pine (Pinus ponderosa), co-dominant with Oregon white oak (Quercus garryana). Ponderosa may be the canopy dominant but is considerably smaller than ponderosa grown in other environments. Except for an occasional Douglas fir (Pseudotsuga menziesii) around Mt. Hood and incense cedar (Calocedrus decurrens) in the Rogue River Valley other trees are absent from this type. Locally, white oak can be very dense. Shrub cover is typically sparse in this type, but rich in herbs and grasses.

Composition. Overstory tree species are ponderosa and white oak. Commonly associated shrubs with the type include: squaw carpet (Ceanothus prostratus), deerbrush (C. integerrimus), snowberry (Symphoricarpos mollis), serviceberry (Amelanchier alnifolia) and bitterbrush (Purshia tridentata).

Commonly associated forbs include western yarrow (Achillea millefolium), hawkweed (Hieracium albiflorum), smooth prairiestar (Lithophragma glabra), American vetch (Vicia americana), tailcup lupine (Lupinus caudatus), arrowleaf balsamroot (Balsamorhiza sagittata), and nineleaf lomatium (Lomatium triternatum). Indicator grasses include: prairie junegrass (Koeleria macrantha), Idaho fescue (Festuca idahoensis), California brome (Bromus carinatus), cheatgrass (B. tectorum), bluebunch wheatgrass (Agropyron spicatum), elk sedge (Carex geyeri), and bulbous bluegrass (Poa bulbosa).

Landscape Setting. The ponderosa/white oak type is an indicator of warm, dry environments.

This type usually forms the lower treeline zone and grades into unimproved pastures that were formerly grasslands. Grazing and selective logging pressure is high in these easily accessible environments. Frequent disturbance will decrease abundance of ponderosa and promote the spread of white oak.

References. Eyre 1980, Kagan and Caicco 1992, Topik et al. 1988, Williams, 1978.