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NORTH PACIFlC
Black Cottonwood- Willow
"Fore:; -+e>tS
222
Definition and composition. -Black cottonwood
generally comprises the majority of the stocking and
sometimes is pure, but arborescent willows often
are present in mixture and may predominate lo­
cally. Major willow species include Pacific, north­
west, river, and,.Scouler willow (Franklin and
Dyrness 1973). Red alder may be present. Minor as­
sociates in the type include bigleaf and vine maples,
Oregon ash, black hawthorn, and other bottomland
hardwood species. Occasionally, Douglas-fir, grand
fir, western hemlock, Sitka spruce, and western
redcedar may occur. Stands are even aged and usu­
ally originate on moist alluvial soU which was bared
or ne'f.lY deposited by flooding.
Geographic . distribution.-The black cotton­
wood-willow type is widespread and occurs on
bottomlands, river bars, and forest meadows and
stream banks of the Pacific Coast from COok Inlet in
coastal Alaska to southern California. It is rare in
the islands of the Alexander Archipelago, where red
alder is common (Viereck and Little 1972). Con­
versely, on the mainland of British Columbia it is
prevalent and extends far up the Fraser, Skeena,
and other rivers into the interior, where the red
alder type is absent. The black cottonwood-wil­
low type is common along the bottomlands of the
Columbia and WUlamette rivers as well as along
major rivers origin,ting on the west side of the Cas­
cade Range in Oregon and Washington.
Ecological relati nships.- The type .is seral and
colonizes freshly exposed sandbars and banks along
rivers and streams (Maini and Cayford 1968). Black
cottonwood is very intolerant of shade, has rapid
early growth, and can compete favorably with
slower,.growing associates. It is a prolific seeder,
but successful establishment requires favorable.
seedbed conditions-wet river bottoms or. other
moist, bare humus or sandy soils. The species can
maintain itself by sprouting from stumps an .roots.
It also has the unusual ability to abscise small shoots
complete with greJn leaves (Galloway·imd Worrall
1979). These drop to the ground and may root
where they fall or be dispersed by water transport.
In some situations, abscission. may be one means of
colonizing exposed sandbars.
Black cottonwood may live to be 200 years old or
more but, barring recurrent catastrophes such as
flooding, it eventually m y be replaced by forest
types composed of shade-tolerant conifers. The type
is best developed in lowland floodplains of .major
rivers in Washington, Oregon, and souther British
Columbia. In some locatipns the willow ·compo­
nent, in combination with lesser vegetation, may
form a nearly impenetrable understory (Franklin
and Dyrness 1973). Shrub species readily claim low­
land sites where black cottonwood and wlllows ei­
ther have not regenerated successfully or have been
kill.ed or damaged by destructive agents such 1l5 fire.
-
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c,
Variants and associated vegetation. -This type
extends inland to meet other closely related types
and forms complex transition zones. In south cen­
tral Alaska, British Columbia, and northern Idaho
and Montana, the type meets forests of balsam pop­
lar and birch. At low elevations in the interior and
semiarid regions of the western United States, the
cottonwood--willow type (No. 235) predominates.
The latter is distinguished from the black cotton
wood-willow, type by absence of any arborescent
alders.
Good sites for black cottonwood and willow are
characterized by salmonberry, stinging nettle,
swordfern, and ladyfern, as well as by vigorous
gro h of hazel and elderberry. On medium sites,
red-osier dogwood, bearberry honeysuckle, and
common snowberry are dominant shrubs. Horse­
tails are most prevalent on poor sites subject to pro­
longed flooding (Smith 1957).
DEANs. DEBELL
USDA Forest Service
Pacific Northwest Forest and
Range Experiment Station
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