This habitat description is reprinted by permission from the report:  Kiilsgaard, C. 1999. "Land Cover Type Descriptions, Oregon Gap Analysis (1998 Land Cover for Oregon)." Oregon Natural Heritage Program, Portland, OR.


STREAMSIDE ALDER/ COTTONWOOD
(formerly termed Red Alder (63)
& Red Alder/Big Leaf Maple Forest (64))

Geographic Distribution. Lowland riparian and low montane forest common in northwestern Oregon and found throughout the Coast Range mountains and the low elevation forests along the western margin of the Cascades. Big leaf maple (Acer macrophyllum) is most prevalent in the foothills region of the Cascades and the eastern side of the Coast Range. Maple is a minor deciduous component along the coastal margin.

Structure and Appearance. Moderate height (20-50 feet) closed canopy deciduous forest. Upland red alder (Alnus rubra) and alder/big leaf maple forests are early seral forests to the low elevation conifer forests of Douglas fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western red cedar (Thuja plicata). Red alder also is a common overstory tree along many streamside corridors within the Coast Range.

Composition. In early seral stages red alder and big leaf maple dominate the overstory. As the stand matures conifers overtop the deciduous trees and dominate the crown layer. In this advanced forest successional stage deciduous trees maintain a hold within the stand as sub-canopy trees in the large gaps among the overstory conifers.

Understory vegetation is prominent and diverse. Indicator shrubs are vine maple (Acer circinatum), salmonberry (Rubus spectabilis), thimbleberry (R. parviflorus), evergreen huckleberry (Vaccinium ovatum), and salal (Gaultheria shallon).

Herbaceous layer is rich in species and usually has one or more of the following moist site indicators: oxalis (Oxalis oregana), swordfern (Polystichum munitum), foamflower (Tiarella trifoliata), vanillaleaf (Achlys triphylla), beadlily (Clintonia uniflora), skunk cabbage (Lysichitum americanum), coltsfoot (Petasites frigidus), and twinflower (Linnaea borealis).

Landscape Setting. Alder stands are important colonizers of sites following timber harvest and act to stabilize hill slopes and retard erosion. Alder and big leaf maple stands are indicative of warm, moist sites. Alder regeneration and establishment is always better on southerly exposures.