DOUGLAS FIR-OREGON WHITE OAK FOREST (53)

Geographic Distribution. Foothills forest type found in the Willamette and western interior valleys of western Oregon. The type is also found in diminishing frequency in the Puget Trough of western Washington. This particular cover type description will pertain to the Willamette Valley communities.

Structure and Appearance. Mosaic cover type where patterns of dominance and co-dominance between Douglas fir (Pseudotsuga menziesii) and Oregon white oak (Quercus garryana) vary based on local environment and stand history. Understory vegetation conditions range widely as well. Ungrazed stands can have prominent shrub and herbaceous layers, while stands that are part of unmanaged pasture mosaics typically have understories where introduced annual grasses dominate.

Composition. Douglas fir and Oregon white oak are the dominant overstory trees. Grand fir (Abies grandis) and Pacific madrone (Arbutus menziesii) may be present, but limited in numbers. Sub-canopy tree layers can be dense in some stands and dominated by California hazelnut (Corylus cornuta), the invasive sweet cherry (Prunus avium), black hawthorn (Crataegus douglasii), and Indian plum (Oemleria cerasiformis).

Commonly associated shrubs for this type include poison oak (Rhus diversiloba), tall OregongrapeOregon-grape (Mahonia aquifolium), snowberry (Symphoricarpos mollis), trailing blackberry (Rubus ursinus), serviceberry (Amelanchier alnifolia), and baldhip rose (Rosa gymnocarpa).

The grass and forb layer typically includes cleavers (Galium aparine), blue wildrye (Elymus glaucus), western iris (Iris tenax), bracken (Pteridium aquilinum), hairy honeysuckle (Lonicera hispidula), and a variety of introduced grasses that seed in from adjacent pasturelands.

Landscape Setting. Hot, dry forests on the fringe between coniferous and valley bottom. Moisture is probably the most limiting characteristic. Douglas fir is invading these predominantly white oOak stands so stand composition typically grades from white oak dominance at lower treeline to co-dominance as the type merges with adjacent conifer forests. The hot, dry conditions of this cover type preclude seedling establishment of shade tolerant conifers, i.e. western hemlock (Tsuga heterophylla) and western red cedar (Thuja plicata). It is the lack of regeneration (and eventual stand succession), of shade tolerant species that distinguishes this cover type from the more mesic upslope conifer forest types.

References. Chappell et al. 1998