Populus balsamifera ssp. trichocarpa

Salicaceae -- Willow family

    Dean S. DeBell

    Black cottonwood (Populus trichocarpa) is the largest of  the American poplars and the largest hardwood tree in western  North America. Known also as balsam cottonwood, western balsam  poplar, and California poplar, it grows primarily on moist sites  west of the Rocky Mountains. The most productive sites are the  bottom lands of major streams and rivers west of the Cascade  Range in the Pacific Northwest. Pure stands may form on alluvial  soils. Black cottonwood is harvested and used for lumber, veneer,  and fiber products. Many kinds of wildlife use the foliage,  twigs, and buds for food, and the tree is planted for shade and  in windbreaks and shelterbelts.

General: Willow Family (Salicaceae). These are native trees up to 30-60 m tall, usually with a straight, branch-free trunk for more than half its length, forming a broad, open crown in open sites; bark gray to gray-brown on mature trees, deeply furrowed into flat ridges on older portions. The leaves are deciduous, simple, alternate, ovate-lanceolate to deltate but variable in size and shape on same tree, rounded or cordate at base, 7-12 cm long, 3.5-7.5 cm wide, hairless or nearly so, the margins finely toothed, dark green above and slightly paler beneath, commonly with whitish or brownish resin blotches, turning yellow in autumn, the petioles round, 3-4 mm long. Flowers male (staminate) and female (pistillate), on separate trees (the species dioecious), each type borne in pendent catkins, the female elongating to 6-8 cm long. Fruits nearly globular capsules 3-4 mm long, splitting to release the seeds; seeds ca.2 mm long, each with a tuft of long, white, silky hairs (“cotton”), easily blown by the wind. The common name is in reference to the dark colored bark.

Black cottonwood is the largest American poplar and the largest hardwood tree in western North America.

Variation within the species: black cottonwood is most commonly and widely known as the distinct species Populus trichocarpa but is sometimes treated as Populus balsamifera var. trichocarpa, the western North American segment of the broader species P. balsamifera (Brayshaw 1965, 1976). Black cottonwood and balsam cottonwood have similar appearances, biological features, and ecology, and they hybridize and introgress where their ranges overlap. Still, they have essentially separate geographic ranges, and, like various other species of Populus that are separated by relatively small differences, black cottonwood and balsam poplar differ in a number of technical features, as partly summarized here.

1. Petioles 7-10 cm long, often with glands at base; terminal bud with 5 scales; staminate catkins 7-10 cm long; mature pistillate catkins 10-13 cm long; fruits ovoid, 6-7 mm long, splitting into 2 parts. .......... P. balsamifera

1. Petioles 3-4 cm long, without basal glands; terminal bud with 6-7 scales; staminate catkins 4-5 cm long; mature pistillate catkins 12-15 cm long; fruits nearly globular, 3-4 mm long, splitting into 3 parts. ........ P. trichocarpa

Brayshaw has recognized two varieties within “subsp. trichocarpa:” Var. trichocarpa (in central and coastal British Columbia and southward) and Var. hastata (Dode) Brayshaw (mainly in the Rocky Mountain region and central British Columbia)

Natural hybrids occur between black cottonwood and other species: narrowleaf cottonwood (P. angustifolia), eastern cottonwood (P. deltoides), Fremont’s cottonwood (P. fremontii), and rarely even aspen (P. tremuloides).

Common black cottonwood, balsam cottonwood, western balsam poplar, California poplar; Populus trichocarpa Torr. & Gray

Black cottonwood is distributed from the Kenai Peninsula of Alaska to Baja
California, east to Nevada, Utah, Wyoming, Idaho, Montana,
North Dakota, and Alberta [77]. 
The U.S. Geological Survey provides a map of black cottonwood's distribution (follow the link to Populus trichocarpa).

In Alaska and the Yukon Territory, black cottonwood
is primarily a coastal species, though 2 interior populations have been
studied in the Yukon [73]. Black cottonwood is present in British Columbia in
a thin strip along
the coast in the northern portion of the province and across most of the southern
portion [28]. It is present in only in the southwestern part of Alberta, often intergrading
with balsam poplar [69]. In Montana, black cottonwood is widespread west of the continental divide, and present in central and eastern Montana
in higher elevations [59]. In California black cottonwood is
widespread, though absent from the Mojave and Sonoran deserts of the southeastern
portion of the state [67]. The species is present throughout Idaho,
Washington, and Oregon. Black cottonwood is not widespread in Utah, Wyoming, or North Dakota. It is
found only in
Utah, Washington, and Wasatch counties in Utah; in Sweetwater,
Uinta, and Teton counties of Wyoming; and in
Foster, Golden Valley, Grand Forks, Grant, and Griggs counties of North Dakota
[37]. Black cottonwood is present only in the northern part of the Baja
California in 2 isolated populations [67,98].

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

BLM PHYSIOGRAPHIC REGIONS [13]:

2 Cascade Mountains

3 Southern Pacific Border

4 Sierra Mountains

5 Columbia Plateau

6 Upper Basin and Range

8 Northern Rocky Mountains

16 Upper Missouri Basin and Broken Lands

AKCAIDMTNVNDORUTWAWY

ABBCYK
MEXICO

The range of black cottonwood extends northeast from Kodiak Island  along Cook Inlet to latitude 62° 30° N., then southeast  in southeast Alaska and British Columbia to the forested areas of  Washington and Oregon, to the mountains in southern California  and northern Baja California (lat. 31° N.). It is also found  inland, generally on the west side of the Rocky Mountains, in  British Columbia, western Alberta, western Montana, and northern  Idaho. Scattered small populations have been noted in  southeastern Alberta, eastern Montana, western North Dakota,  western Wyoming, Utah, and Nevada.

   
  -The native range of black cottonwood.

Populus trichocarpa var. ingrata (Jeps.) Parish:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Populus trichocarpa Torr. & A. Gray:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Populus balsamifera subsp. trichocarpa (Torr. & A. Gray) Brayshaw:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Canada

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Black cottonwood grows on alluvial sites, riparian habitats, and moist woods on mountain slopes, at elevations of 0–2100(–2750) meters. It often forms extensive stands on bottomlands of major streams and rivers at low elevations along the Pacific Coast, west of the Cascade Range. In eastern Washington and other dry areas, it is restricted to protected valleys and canyon bottoms, along streambanks, and edges of ponds and meadows. It grows on a variety of soils from moist silts, gravels, and sands to rich humus, loams, and occasionally clays.

Black cottonwood is a pioneer species that grows best in full sunlight and commonly establishes on recently disturbed alluvium. Seeds are numerous and widely dispersed because of their cottony tufts, enabling the species to colonize even burn sites, if conditions for establishment are met. Seral communities dominated or codominated by cottonwood are maintained by periodic flooding or other types of soil disturbance. Black cottonwood has low drought tolerance; it is flood-tolerant but cannot tolerate brackish water or stagnant pools.

Flowering occurs in late March to May (-June), just before or during leaf emergence and fruiting occurs in late May to early or mid-July.

The range of black cottonwood extends from Alaska, including various islands, through coastal regions of western Canada (Yukon, British Columbia, and Alberta) into the northwestern US (Washington, Oregon, Montana, Idaho, and Nevada; rare in North Dakota, Wyoming, Utah, and California) and as far south as Baja California Norte. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

More info for the term: tree

Black cottonwood typically has a straight, branch-free trunk for more than half
its length and a broad, open crown [11]. In closed stands, the crown tends to be
narrow, with few branches growing into the lower 2/3rds of the trunk [117].
Black cottonwood develops extensive forests along major rivers, narrow forests
along smaller streams, and sometimes irregular populations on gravel bars,
floodplains, and terraces [58]. Establishment by seed is episodic, often creating
stands of several well-defined age groups [89]. Black cottonwood is a fast growing,
native deciduous tree, growing to 100 feet (30 m)
high [36,159] though occasionally as high as 160 feet (50 m) [159]. Basal diameter is commonly 3.5 to 5 feet (1-1.5 m)
[36,159]. Black cottonwood commonly lives 100 to 200 (or occasionally more)
years [19].

Flowers grow in catkins. Staminate catkins are
usually about 1 inch (2-3 cm) long, though occasionally up to 2 inches (5 cm)
long. Pistillate catkins are 3 to 8 inches (8-20 cm) long
[68]. Capsules are subsessile and 0.2 to 0.32 inch (5-8 mm) long; each
capsule contains 3 (occasionally 2 or 4) carpels [156]. Seeds bear long, white, "cotton" fibers that aid in
dispersal via wind and/or water [57]. Each cottonwood seed weighs approximately
0.3 to 0.6 mg [19].

Much
genetic variation occurs in black cottonwood with respect to flooding
tolerance [130] and cold tolerance [92]; responses to these
extremes are influenced by the site from which experimental
cuttings are gathered [92,130].

Roots: Black cottonwood develops a "shallow,
spreading root system" [11]. In the Tacamahaca section rooting depth
is commonly 10 to 16 feet (3-5 m), occasionally deeper [19]. Roots
of the Populus genus have well-developed laterals. Eighty percent of the roots of a black cottonwood × plains
cottonwood hybrid were horizontal roots (oriented between 0° and 30°).
Horizontal roots grow between approximately 2 and 8 inches (5 to 20 cm) below
the soil surface. Some roots observed in this study, termed
"sinker" roots, originated as horizontal roots, extended laterally a
short distance, and then grew downward much like a taproot [113]. 
Fine root production in black cottonwood is episodic and much
more variable than the production and survival of leaves [113].

Mycorrhizal colonization of cottonwoods may be influenced by
stand development stage and site characteristics. Members of the Populus genus are typically
ectomycorrhizal [38,113,148], but may be colonized by
arbuscular mycorrhizal
fungi early in stand development or when the site is flooded [38].

More info for the terms: association, codominant, cover, density, fern, forbs, shrub, shrubs, tree

Alaska: In the Tanana, Yukon, and Susitna valleys, black cottonwood and
balsam poplar stands are some of the most productive in Alaska. American green alder
(Alnus viridus var. crispa) and thinleaf alder (A. incana subsp.
tenuifolia) are usually present throughout stand development; willows (Salix
spp.) are less
common when cottonwood and balsam poplar are mature. Common
associates include prickly rose (Rosa acicularis), viburnum (Viburnum spp.),
red-osier dogwood (Cornus sericea), devil's club (Oplopanax horridus),
horsetails (Equisetum spp.), and bluejoint (Calamagrostis canadensis) [101].
On Sheep Creek, near Juneau, Alaska, black cottonwood grows with salmonberry (Rubus
spectabilis), elderberry (Sambucus spp.), cranberry, and Sitka alder (Alnus
viridis subsp. sinuata) [12]. On the Kenai Peninsula black cottonwood is common on wet
sites; co-dominants include balsam poplar, black spruce (Picea mariana),
Scouler's willow (Salix scouleriana), Barclay's willow (S. barclayi), and
American green alder [135,155].

Yukon: Stanek and others [137] describes "Populus balsamifera"
(likely including black cottonwood, balsam poplar, and their hybrids) in
the mountain alder (Alnus incana)-balsam poplar-field horsetail (Equisetum arvense)
vegetation type as well as the balsam poplar-arctic lupine (Lupinus arcticus)-bog birch (Betula nana) vegetation type. The
former is confined to permafrost-free terraces and floodplains,
and the latter is present on southwest aspects on lower slopes on alluvium.

British Columbia: On floodplains, black cottonwood is
dominant, commonly with red-osier dogwood. Western redcedar (Thuja
plicata) and hybrid white spruce (Picea glauca) × Engelmann
spruce (P. engelmannii), though present,
typically do not become dominant because of frequent flooding and sediment
deposition [57]. Other codominants in these black cottonwood communities include
Pacific willow (Salix lucida subsp. lasiandra), red alder (Alnus rubra),
Sitka alder, Himalayan blackberry (Rubus discolor), devil's club, stink
currant (Ribes bracteosum), and
occasionally Sitka spruce (Picea sitchensis) [81]. Forbs in
black cottonwood dominated floodplains include fragrant bedstraw (Galium triflorum), horsetails,
liverleaf wintergreen (Pyrola asarifolia), small enchanter's nightshade (Circaea
alpina), common lady
fern (Athyrium filix-femina), starry false Solomon's-seal (Maianthemum
stellatum), sweetcicely (Osmorhiza berteroi), dwarf red blackberry (Rubus
pubescens), bride's feathers (Aruncus dioicus), common cowparsnip (Heracleum
maximum), stinging nettle (Urtica dioica), slough sedge (Carex obnupta), and
arctic sweet coltsfoot (Petasites frigidus var. palmatus) [57]. 
Along the Blaeberry River near Golden, British Columbia, black cottonwood and
white spruce are codominant on "stable" islands; dwarf fireweed (Epilobium latifolium)
is dominant in the understory
and Hervey's aster (Aster hesperius), Lindley's aster (A. ciliolatus),
scarlet Indian paintbrush (Castilleja
miniata), northern green orchid (Platanthera hyperborea), and
Aleutian selfheal (Prunella vulgaris) are also present [46].
Other woody species in these floodplain communities include quaking aspen (Populus
tremuloides), Farr's willow (Salix farriae), and Wolf's willow (S. wolfii).

Western Washington: Black cottonwood is an early
seral species in western hemlock (Tsuga heterophylla) communities including
western hemlock/skunk cabbage (Lysichiton americanus), western hemlock/common lady fern, and western
hemlock/devil's club habitat types. It is also present in wet and/or cool
grand fir (Abies grandis), Douglas-fir, and western redcedar habitat
types [147]. On the Hoh River on the Olympic Peninsula, a Sitka spruce-bigleaf maple-black cottonwood association occurs
on first terraces. Subdominant trees include red alder and Douglas-fir and
western hemlock if the site is not disturbed. The understory of these communities includes
the grasses redtop (Agrostis gigantea) and fowl bluegrass (Poa palustris) and the forbs
Oregon oxalis (Oxalis oregana), western sword fern (Polystichum munitum), and
small enchanter's nightshade [44].

Eastern Washington and northern Idaho: Black
cottonwood frequently occurs (though never in great abundance) in the seral
stages of the development of western hemlock and western redcedar habitat types,
and is sometimes a minor component of old-growth stands of these types [99].
Black cottonwood is prevalent at lower elevations on floodplains and
terraces where frequently it is mixed with ponderosa pine and Douglas-fir
[33,88]. In drier
areas, like the Palouse River, black cottonwood is dominant with western water
hemlock (Cicuta douglasii) dominant in the understory. Many of these communities have been
disturbed by human activities [32]. In mountainous areas of
eastern Washington, Idaho, and northwestern Montana, black cottonwood sometimes
grows in avalanche chutes with mountain alder, Saskatoon serviceberry, Rocky Mountain maple (Acer glabrum), and quaking aspen
[56].

Oregon: In bottomland forests of the Willamette
Valley of western Oregon, black cottonwood, Douglas-fir (Pseudotsuga
menziesii), big-leaf maple (Acer macrophyllum), and
white ash (Fraxinus americana) are common, all occurring with about the same density.
Subdominant trees in these communities include
Oregon white oak (Quercus garryana), California laurel (Umbellularia californica),
alder (Alnus spp.), bitter cherry (Prunus emarginata), and willows, and the understory usually includes Oregon- grape (Mahonia
repens), salmonberry, rose (Rosa spp.), Douglas' spiraea (Spiraea
douglasii), Pacific ninebark (Physocarpus capitatus), and Pursh's
buckthorn (Frangula purshiana).
Many of
these community types have declined due to cultivation and hydrologic
alterations [54,136]. In the Catherine Creek watershed of eastern
Oregon, black cottonwood is dominant with ponderosa pine (Pinus
ponderosa) in structurally diverse riparian communities.
Subdominants include mountain alder, black hawthorn (Crataegeus
douglasii), Woods' rose, Kentucky bluegrass (Poa pratensis), and common snowberry
(Symphoricarpos albus). Black
cottonwood is commonly the only tree present on recently formed gravel bars
[79].

California: In the North Coast Ranges and Klamath Mountains,
black
cottonwood grows with red alder; older stands with less disturbance also
support grand fir, Sitka spruce, Douglas-fir, western redcedar, or western
hemlock. Black cottonwood is dominant in montane riparian forests of the Sierra Nevada
where Jeffrey pine (Pinus jeffreyi) is a common associate; shrub cover
(red-osier
dogwood, western juniper (Juniperus occidentalis), willows, and common
chokecherry) is commonly about 25% [70]. In southern California, Fremont cottonwood is dominant along
washes and streams in lower elevations and black cottonwood is dominant in
similar habitats at higher elevations [108,146]. Common associates
in the black cottonwood communities include bigleaf maple, white alder (Alnus rhombifolia),
willows, and California laurel [146]. In the South Coast Ranges, Fremont cottonwood and
California sycamore (Platanus
racemosa) are dominant, but black cottonwood and coast live oak (Quercus agrifolia) are also
present [70]. Off the coast near Santa Barbara, on Santa Rosa,
Santa Cruz, and Santa Catalina islands, riparian woodlands are dominated by
black cottonwood with Fremont cottonwood; Tracy willow (Salix lasiolepis var.
lasiolepis) and blue elder (Sambucus mexicana) are also present. Herbaceous vegetation
consists of saltgrass (Distichlis spicata), annual rabbitsfoot
grass (Polypogon monspeliensis), redtop, and tropical medicineplant (Adenostoma
verbesina) [27,110]. Near drainageways in the San Dimas Forest near Los Angeles, black
cottonwood is a dominant with coast live oak, California sycamore, bigleaf
maple, white alder, and willows in open stands [40].

Alberta: In southern Alberta, most riparian
communities in the semi-arid portion of the province are dominated by cottonwoods, including black
cottonwood, eastern cottonwood (Populus deltoides),  narrowleaf
cottonwood (P. angustifolia), and balsam poplar. Shrubs include common chokecherry (Prunus virginiana), Saskatoon serviceberry (Amelanchier
alnifolia), Wood's rose, and
western snowberry (Symphoricarpos occidentalis) [49].

North Dakota: Black cottonwood occurs with green ash
(Fraxinus pennsylvanica) and American elm (Ulmus americana) in riparian areas in western North Dakota
[71].

Montana: In
western Montana, the most common codominant tree with black cottonwood is ponderosa
pine. Others include Douglas-fir, Engelmann spruce, western redcedar, Rocky Mountain juniper
(Juniperus scopulorum), and
quaking aspen. The shrub component includes Wood's rose, mountain alder, Bebb willow (Salix
bebbiana), common chokecherry, red-osier dogwood,
western snowberry, and common snowberry
[60]. Herbaceous
species commonly dominant include quackgrass (Elytrigia repens),
Kentucky bluegrass, creeping bentgrass (Agrostis
stolonifera), starry false Solomon's seal, Virginia strawberry (Fragaria virginiana), and
fragrant bedstraw [60,62]. In central and eastern Montana black cottonwood grows with narrowleaf and
eastern cottonwoods in transitional zones (narrowleaf and eastern cottonwoods
are dominant at lower elevations) [60]. Along the North Fork of the
Flathead River, near Glacier National Park, 3 black cottonwood community
types were studied by Jenkins and Wright [75].  In early successional
communities the black cottonwood overstory is approximately 50%. Coniferous
canopy cover is low (<5%), and shrubs are not prominent. Other species
present on these sites include common yarrow (Achillea millefolium),
mountain alder, asters (Aster spp.), fireweed (Epilobium spp.),
prairie Junegrass (Koeleria macrantha), timothy (Phleum pratense),
bluegrass (Poa spp.), and Canada goldenrod (Solidago canadensis).
In later-successional community types the canopy cover of hybrid spruce (white
spruce × Engelmann spruce) increases to approximately 50% and gradually
replaces black cottonwood. Shrubs include red-osier dogwood, roses (Rosa
spp.), and common snowberry; these species become less prominent with increasing
hybrid spruce canopy cover.

Eastern and southern Idaho: Black cottonwood/red-osier dogwood is a common community type; it develops best along large rivers but
is also present in narrow bands along small streams in the subalpine zone [58]. Subdominant members of the
overstory include narrowleaf cottonwood,  lanceleaf cottonwood (P. acuminata),
and peachleaf willow (Salix amygdaloides var. wrightii). Common shrub associates include
sandbar willow (Salix exigua), water birch (Betula occidentalis), yellow willow
(Salix lutea), and Wood's rose [58,74].

Nevada: Confined to riparian areas, black cottonwood commonly grows with
lanceleaf and narrowleaf cottonwoods, with these 3 species having
approximately 85% canopy cover. Wood's rose is prominent in
these habitats (25-90% canopy cover); currants (Ribes spp.) and
red-osier
dogwood are also common [90]. In central Nevada, black cottonwood
is sometimes associated with big sagebrush (Artemisia tridentata) [15]. 

Classifications describing plant communities in which black cottonwood is a
dominant species are as follows:

Alaska [17,153]

California [27,70,108,147]

Idaho [58,74,149]

Nevada [90]

Montana [60,61,62,111]

Oregon [54,79,82]

Washington [32]

Wyoming [105]

British Columbia [81]

Yukon [137]

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This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

More info for the terms: cover, forb, shrub

SRM (RANGELAND) COVER TYPES [129]:

107 Western juniper/big sagebrush/bluebunch wheatgrass

109 Ponderosa pine shrubland

110 Ponderosa pine-grassland

201 Blue oak woodland

202 Coast live oak woodland

203 Riparian woodland

205 Coastal sage scrub

314 Big sagebrush-bluebunch wheatgrass

315 Big sagebrush-Idaho fescue

316 Big sagebrush-rough fescue

324 Threetip sagebrush-Idaho fescue

401 Basin big sagebrush

402 Mountain big sagebrush

403 Wyoming big sagebrush

404 Threetip sagebrush

405 Black sagebrush

406 Low sagebrush

407 Stiff sagebrush

408 Other sagebrush types

409 Tall forb

422 Riparian

901 Alder

917 Tall shrub swamp

921 Willow

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

More info for the term: cover

SAF COVER TYPES [42]:

16 Aspen

18 Paper birch

63 Cottonwood

201 White spruce

202 White spruce-paper birch

203 Balsam poplar

205 Mountain hemlock

206 Engelmann spruce-subalpine fir

210 Interior Douglas-fir

211 White fir

212 Western larch

213 Grand fir

215 Western white pine

216 Blue spruce

217 Aspen

218 Lodgepole pine

220 Rocky Mountain juniper

221 Red alder

222 Black cottonwood-willow

223 Sitka spruce

224 Western hemlock

225 Western hemlock-Sitka spruce

226 Coastal true fir-hemlock

227 Western redcedar-western hemlock

228 Western redcedar

229 Pacific Douglas-fir

230 Douglas-fir-western hemlock

233 Oregon white oak

234 Douglas-fir-tanoak-Pacific madrone

235 Cottonwood-willow

237 Interior ponderosa pine

243 Sierra Nevada mixed conifer

244 Pacific ponderosa pine-Douglas-fir

246 California black oak

247 Jeffrey pine

249 Canyon live oak

250 Blue oak-foothills pine

251 White spruce-aspen

252 Paper birch

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

KUCHLER [84] PLANT ASSOCIATIONS:

K001 Spruce-cedar-hemlock forest

K002 Cedar-hemlock-Douglas-fir forest

K003 Silver fir-Douglas-fir forest

K004 Fir- hemlock forest

K005 Mixed conifer forest

K008 Lodgepole pine- subalpine forest

K011 Western ponderosa forest

K012 Douglas-fir forest

K013 Cedar-hemlock-pine forest

K014 Grand fir-Douglas-fir forest

K015 Western spruce- fir forest

K016 Eastern ponderosa forest

K017 Black Hills pine forest

K025 Alder-ash forest

K026 Oregon oakwoods

K028 Mosaic of K002 and K026

K029 California mixed evergreen forest

K030 California oakwoods

K055 Sagebrush steppe

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

ECOSYSTEMS [48]:

FRES20 Douglas-fir

FRES21 Ponderosa pine

FRES22 Western white pine

FRES23 Fir-spruce

FRES24 Hemlock-Sitka spruce

FRES25 Larch

FRES26 Lodgepole pine

FRES28 Western hardwoods

FRES29 Sagebrush

Soils: Hansen and others [60] state that black cottonwood mature stands "occur
on a wide range of soil textures but are most numerous on medium- to
coarse-textured, well-drained soils [60]. Soils are Mollisols in older
communities and Fluvents in younger communities [62]. Black cottonwood
has high nutrient requirements, particularly for calcium and magnesium and is,
for this reason, not common on soils characterized by acid humus [57].
Optimal soil pH for black cottonwood growth is between 5 and 7 [19,57]. On the Blaeberry River,
British Columbia, black cottonwood grew on stable coarse-textured
islands, never in silty depression areas; these were dominated by sedges (Carex spp.)
[46].

Climate: Black cottonwood grows in a wide variety of climates, including coastal
areas receiving 140 inches (3,500 mm) of annual precipitation and arid areas receiving
6 to 8 inches (150 to 200 mm), though in the latter climate the species is more
restricted to wet habitats [11].  Black cottonwood is not present in the most humid areas
of British Columbia (immediately along the coast); it is more common in "marginally subalpine
climates" [57].

Elevation ranges of black cottonwood are summarized below:

StateElevation rangeReferenceAKsea level-2,000 feet (0-600 m)[35]CA0-10,000 feet in the southern Sierra Nevada, to
9,200 feet (2,800 m) in the northern part of the state[52]ID4,600-7,400 feet (1,390-2,100 m)[58]MT (western)4,600-7,400 feet (1,390-2,100 m), < 4,600 feet
(1,390 m) east of the Continental Divide[58,59]UT4,500-7,700 feet (1,370-2,350 m)[159]WA (Cascade Range)0-5,000 feet (1,500 m)[35]WY (Wind River Range)dominant between 4,500 and 5,000 feet (1,370-1,520 m)[105]BC0-6,900 feet (2,100 m)[57]Baja California 4,600 feet (1,400 m)
and 4,340 feet (1,325 m) [98]

Water table: Harrington [63] states that black cottonwood is very tolerant of short-duration flooding,
and Hansen and others [60] have found it to be "very tolerant of frequent and
prolonged flooding." In any case, the water
level is close to the surface in nearly all areas where black cottonwood is
dominant [45], though sometimes black cottonwood colonizes avalanche
chutes on steep slopes [56]. Because black cottonwood requires water with
dissolved oxygen content, it grows better along moving water than near stagnant
water [57].

Black cottonwood grows on a variety of soils and sites, from moist  silts, sands, and gravels of islands and new river bars to rich  humus soils, loams, and occasionally clay soils of upland sites  (23). The most extensive black cottonwood stands are on soils of  the order Entisols; the species also is common on Inceptisols and  occasionally may be present on soils of other orders. High soil  acidity (low pH) may restrict occurrence of black cottonwood on  fine-textured soils where other site factors are favorable (9).  Studies in British Columbia (27) have indicated that abundant  moisture, nutrients, oxygen, and nearly neutral soil reaction (pH  6.0 to 7.0) are required for optimum production. Growth is best  at low elevations on deep, moist alluvial soils, but some upland  soils are productive cottonwood sites (27). The latter include   loessial soils of high nutrient status in areas of abundant  rainfall.

    Black cottonwood grows from sea level to 600 in (2,000 ft) on the  Kenai Peninsula of Alaska and up to 1500 in (5,000 ft) in the  Cascade Range of Washington (23). In British Columbia, the  elevation range extends to nearly 2100 m (7,000 ft) in the  interior valleys of the Selkirk Range. In central and eastern  Washington, as well as other dry areas, the species is usually  limited to protected valleys and canyon bottoms, along stream  banks and edges of ponds and meadows, and to moist toe slopes.

Populations of black cottonwood grow in climates varying from  relatively and to humid, but best growth is attained in the humid  coastal forests of the Pacific Northwest (23). Annual  precipitation ranges from 250 min (10 in) to more than 3050 min  (120 in). Only about one-third of the annual precipitation occurs  during the growing season, and in mountainous and inland areas  much of the dormant-season precipitation falls as snow. The  frost-free period ranges from about 70 days in the interior areas  to more than 260 days in southern California. Maximum  temperatures range from 16° to 47° C (60° to 117°  F); minimum temperatures, from 0° to –47° C (32°  to –53° F).

Black cottonwood begins producing seed at about 8-10 years – abundant seed is usually produced every year. Seeds under natural conditions are short-lived, usually for less than a month. Seed will readily germinate on a variety of favorable sites, particularly where mineral soil has been exposed or new soil deposited. High germination rates and seedling survival depend on continuously moist conditions, such as in fresh alluvium, during the first month.

Maximum height and size are usually reached in 60-75 years although some may continue to grow well past that. Maximum age is at least 200 years.

Black cottonwood sprouts readily from the stump and roots as well as from branches and logs that are left after logging. Small shoots with green leaves abscise naturally and either root where they fall or are water-transported some distance before they root.

In Great Britain and/or Ireland:
Foodplant / spot causer
mostly hypophyllous uredium of Melampsora allii-populina causes spots on live leaf of Populus trichocarpa

Plant / resting place / within
epiphyllous, subepidermal, grouped, confluent telium of Melampsora laricis-populina may be found in dead, fallen leaf of Populus trichocarpa

Foodplant / parasite
Uncinula adunca var. adunca parasitises Populus trichocarpa

Foodplant / open feeder
adult of Zeugophora subspinosa grazes on leaf of sapling of Populus trichocarpa
Remarks: season: mid 8-9,5-12

Black cottonwood often forms extensive stands on alluvial sites at  low elevations along the Pacific coast. Arborescent willows are  its major associates in two cover types (3): Black  Cottonwood-Willow (Society of American Foresters Type 222) and  Cottonwood-Willow (Type 235). In the latter type, balsam poplar  (Populus balsamifera) is the dominant cottonwood.  Major willow species are Pacific (Salix lasiandra), northwest  (S. sessilifolia), river (S. fluviatilis),  and Scouler (S. scouleriana) willow (4). In  other coastal forests, black cottonwood grows in mixture with red  alder (Alnus rubra), Douglas-fir (Pseudotsuga  menziesii), western hemlock (Tsuga heterophylla), western  redcedar (Thuja plicata), Sitka spruce (Picea  sitchensis), grand fir (Abies grandis), bigleaf maple  (Acer macrophyllum), Oregon ash (Fraxinus latifolia),  black hawthorn (Crataegus douglasii), and several  birch (Betula spp.) and cherry (Prunus spp.)  species. Associates in interior forests may include western white  pine (Pinus monticola), ponderosa pine (P. ponderosa),  white fir (Abies concolor), western larch (Larix  occidentalis), subalpine fir (A. lasiocarpa), white  spruce (Picea glauca), Engelmann spruce (P.  engelmannii), and quaking aspen (Populus tremuloides).

    Shrub species associated with black cottonwood include vine maple  (Acer circinatum), red-osier dogwood (Cornus  stolonifera) and other Cornus spp., beaked  hazel (Corylus cornuta), Nootka rose (Rosa nutkana),  thimbleberry (Rubus parviflorus), salmonberry (R.  spectabilis), elder (Sambucus spp.), bearberry  honeysuckle (Lonicera involucrata), spirea (Spiraea  spp.), and common snowberry (Symphoricarpos albus).

    Herbaceous associates include swordfern (Polystichum munitum),  lady fern (Athyrium filix-femina), horsetail (Equisetum  spp.), stinging nettle (Urtica dioica), hedge nettle  (Stachys spp.), false solomons-seal (Smilacina  stellata), Canada violet (Viola canadensis), jewelweed  (Impatiens spp.), enchanters nightshade (Circaea  alpina), golden-saxifrage (Chrysosplenium spp.),  buttercup (Ranunculus spp.), bittercress (Cardamine  spp.), angelica (Angelica spp.), loosestrife (Lysimachia  spp.), bedstraw (Galium spp.), and iris (Iris  spp.).

    Presence of some of these understory species provides an  indication of site quality in British Columbia (27). Good black  cottonwood sites are characterized by salmonberry, nettles,  swordfern, and lady fern, as well as vigorous growth of beaked  hazel and elder. On medium sites, red-osier dogwood, bearberry  honeysuckle, common snowberry, and sometimes thimbleberry and  Nootka rose are common. Poor sites are commonly subject to  prolonged flooding, and horsetails are dominant.

Young saplings are frequently injured and  sometimes killed by unseasonably early or late frosts (23). Frost  cracks also lower quality of wood and provide an entrance for  decay fungi (30). Ice storms and heavy snowfall cause  considerable breakage and permanent bending (29). Wind damage is  common, especially in stands where black cottonwood trees are  much taller than surrounding vegetation; top breakage and bending  result. Erosion along rivers and major streams also takes its  toll in adjacent black cottonwood stands. The species is highly  susceptible to fire damage.

    Mammals can create serious problems in black cottonwood  plantations, especially at time of establishment or soon after.  Meadow voles and meadow mice can cause severe losses in young  plantations; such damage occurs most commonly on grassy or  herb-covered sites. The voles feed on roots and sometimes girdle  the lower stem. In some locations, rabbits and hares cause losses  in young cottonwoods via clipping and basal girdling damage.  Damage also results when beavers use cottonwood for food and  construction of dams. Browsing and trampling of saplings by elk  and deer sometimes decimate small, isolated plantings. Slugs have  girdled cottonwood stems and presumably have eaten buds and newly  emergent leaves of recently planted cuttings in the lower  Columbia River valley.

    Although several insects attack black cottonwood (5,17), none has  yet been reported as a pest of economic significance. Foliar  feeders include tent caterpillars (Malacosoma spp.),  two sawflies (Phyllocolpa bozemani and Nematus  currani), the satin moth (Leucoma salicis), and a  leaf blotch miner (Agromyza albitarsis). Oystershell  scale (Lepidosaphes u1mi) was reported as frequently  killing twigs and branches, and sometimes a whole tree. A bud  midge (Contarinia spp.) caused considerable  injury to buds of stressed trees (e.g., nursery-grown trees that  have been transplanted, and trees on dry sites or in dry years)  (9). A small bark moth (Laspeyresia populana) mines the  cambium of the trunk and larger branches. Two borers feed under  the bark and in the wood, a flatheaded borer (Poecilonota  montana) and the poplar- and-willow borer (Cryptorhynchus  lapathi). The latter is a European insect that is now  established throughout much of the range of black cottonwood and  has caused some damage in cottonwood plantings. Other flatheaded  and roundheaded borers and ambrosia beetles are known to destroy  the wood of black cottonwood.

    At least 70 fungal species cause decay in cottonwood, but only six  fungi cause significant losses in British Columbia; two of these  (Spongipellis delectans and Pholiota destruens) cause  92 percent of the loss (15,17,33). A leaf rust (Melampsora  spp.) has been observed in young plantations, and  susceptibility to the rust appears to vary greatly across the  geographic range of the species. This disease limits  photosynthesis and causes leaves to fall prematurely, thereby  decreasing tree growth and vigor. Severe Melampsora infections  have been observed when clonal material from relatively dry areas  (e.g., east of the Cascade Range in Washington or Oregon and  northern California) was planted in western Washington (9); in  one instance, such infections resulted in death of the clones.  Other foliage diseases include leaf-spot syndrome (Venturia  populina) and yellow-leaf blister (Taphrina  populisalicis). A deformity of catkins is caused by Taphrina  johansonii. Cytospora canker (Cytospora chrysosperma) is  widespread under forest conditions but rarely causes  significant damage in vigorous cottonwood stands. It may cause  problems, however, to cuttings in nurseries and plantations. Stem  cankers in various areas have been reported as caused by Dothichiza  populea, Fusarium spp., Hypoxylon mammatum, Nectria galligena,  and Septoria musiva. None appear to be of great  significance in management of black cottonwood, but severe  attacks of a bacterial canker have reportedly limited planting of  the species in Europe. Black cottonwood is also subject to the  condition known as wet wood, which leads to wood collapse during  drying.

More info for the term: prescribed fire

To increase the longevity of cottonwood stands managers may choose to prescribe
fire when the stand is in the "pole" stage, as sprouting is high at this point
[58]. Dormant season, particularly fall, fires induce the most sprouting [49]. Gom and Rood [49] suggest that fire- induced sprouting, particularly in old stands,
may be used to regenerate stands much the way flooding disturbance allows
development of new stands. They also state that regeneration may be more rapid
after fire than after flooding because the growth rate of sprouts is about 3 times
greater than that of seedlings.

If the goal of prescribed fire is to maintain a cottonwood stand, 5 years of grazing exclusion
after fire are recommended [58]. Herbivory and fire interactions
have been well documented for quaking aspen stands. In
the Rocky Mountains (study sites ranged from Jasper National Park, Canada to
Rocky Mountain National Park, Colorado), White and others [157] found that prolific quaking
aspen sprouting after fire could not overcome
the effects of elk grazing, and, with a short fire return interval, quaking aspen stands
would decline.

Fire can be used to maintain black cottonwood stands, but it may cause negative impacts such as erosion and sedimentation. These impacts both on the site of fire and
on sites downstream can be increased by heavy postfire rainfall [132].

More info for the terms: density, frequency, tree

One year after the fires along the Oldman River in Alberta (described above),
approximately 75% of the top-killed cottonwoods (including all narrowleaf and
black cottonwoods, and balsam poplar)
produced shoots from remnants of trunks. Sprouting was not observed on
control  transects (on adjacent unburned areas). Of the trunks producing sprouts, 90% were from either
narrowleaf or black cottonwood (the 2 species' sprouts were not easily
differentiated). The average number of coppice sprouts was 17 per trunk with a
range of 1 to 60. Height of the tallest sprout on each tree averaged
16 inches (41
cm) and ranged from 3.5 to 30 inches (9-77 cm). The authors speculated that the high
rate of sprouting was in part due to the occurrence of the fires while the
cottonwoods were dormant. The degree of canopy or trunk damage did not have much impact on coppice
sprouting frequency or vigor. Sprouts were even observed from trunks that had burned
to 10 inches (25 cm) below ground. Of trees that experienced "heavy" canopy damage,
60% produced shoots from stumps; 80% of those with "light" damage produced coppice sprouts. The average height of coppice sprouts was not
significantly (p>0.05) affected by the degree of trunk damage, and trunk diameter had no significant (p>0.05)
effect on either the number of coppice
sprouts or the height of sprouts. Over 1,000 root suckers were observed on the study transects, 80% of which were
either narrowleaf or black cottonwood. The density of root suckers (including
all species) was about 1/ 3 m2). Suckers were
more common near trees that had many coppice sprouts. After 1 growing season the average height of
root suckers was approximately 3 feet (1 m) [49].

Transects on the Oldman River were surveyed again 5 years after fire. At this time there
was an average of 4 coppice sprouts per trunk on the
30% of the cottonwoods that still had living sprouts. Average sprout height was
approximately 10 feet (3 m) with a range of 5 to 16 feet (1.5 to 5 m). Of the 34
trunks with surviving coppice sprouts 33 were either narrowleaf or black
cottonwood and 1 was plains cottonwood. Survival of root suckers over the 5 years was about 50%. A density of 1 sprout
per  7 m2 was observed as 550 sprouts still survived on the transects. The
average height of root suckers increased from about 3 feet (1 m) to 8 feet (2.4
m). Seven root suckers were present on unburned control sites; the authors
stated that these might have been induced by flooding damage 2 years prior to
the survey [49].

Gom and Rood [49] summarized the response of several cottonwood species to
fire, showing the high sprouting/suckering ability of balsam poplar and black
and narrowleaf cottonwoods relative to Fremont and eastern cottonwoods:

Year of fireLocationAge when studied (years)Cottonwoods affected by fireSuccess of asexual regenerationabout 1988Peace River near Fort St. John, BC~10Balsam poplarVery good (vigorous sucker sprouts)about 1992Red Deer River at Dinosaur Provincial Park, Brooks, AB~5Eastern cottonwoodVery poor1990Belly River at Lavern, AB7Narrowleaf cottonwood, black cottonwoodVery good spring 1992Oldman River at Lethbridge, AB5Narrowleaf cottonwood, balsam poplar, black cottonwood,
eastern cottonwoodGood (sucker and coppice sprouts)about 1986South Saskatchewan River, Police Point Park, Medicine hat,
AB~10Eastern cottonwoodVery poorsummer 1973Milk River near Manyberries, AB 24Eastern cottonwoodVery poorabout 1995Lower Truckee River, near Nixon, NV~2Fremont cottonwoodPoor about 1994Kane Springs Creek, south of Moab, UT~3Fremont cottonwoodPoor (sparse coppice sprouts)

More info for the terms: fire severity, fuel, root crown, severity, top-kill, tree

Black cottonwood sprouts from the lateral roots, root crown, and bole after
top-kill by fire [49,58]. It also establishes from seed [3,24,131,158]. Gom and Rood [49] studied the effects of
severe fires along the Oldman River near Lethbridge, Alberta, which occurred in early and mid-April before cottonwoods' spring bud burst. The fires burned during the afternoon; strong Chinook winds increased fire severity.

Black cottonwood,
narrowleaf cottonwood, plains cottonwood, and hybrids among them dominated
these riparian areas. All cottonwoods observed were girdled by the fires. Fire damage to trunks varied from "slight bark
charring to complete trunk incineration." This caused 100% top-kill in trees even though not
all canopies were severely damaged, demonstrating the susceptibility of these
cottonwood species to severe fires. The exact amount of mortality was not
determined (because it is difficult to tell from which tree's lateral root
system suckers originate), but mortality was definitely less than 25%, as 75% of
trunks (including all species) produced coppice sprouts. The most severe fires were in older
stands, likely the result of higher fuel accumulation, and there were many pits
in the ground on these sites where root systems were burned. Young stands close to the
river (without as much fuel loading) experienced less canopy damage but were top-killed via girdling.

Hardwood saplings (cottonwood, alder, willow) less than 2 inches (5 cm) in
diameter experienced 100% mortality in 168 and 42 BTU/second/foot
intensity fires in a
white spruce, quaking aspen, and balsam poplar (likely including some black cottonwood
and hybrids) stand northeast of Edmonton, Alberta [80]. 

Hall and Hansen [58] stated that in low and moderate severity fires older black
cottonwood trees
with thick bark may not be top-killed, but little quantitative data examining
the relations between fire severity, tree age, and top-kill or mortality is
available.

More info for the term: adventitious

POSTFIRE REGENERATION STRATEGY [140]:

Tree with adventitious bud/root crown/soboliferous species root sucker

Geophyte, growing points deep in soil

Initial off-site colonizer (off-site, initial community)

Secondary colonizer (on-site or off-site seed sources)

More info for the terms: fire exclusion, fire frequency, fire severity, frequency, fuel, fuel loading, litter, resistance, severity

Fire Adaptations: Black cottonwood is frequently damaged by fire with low-severity burns even often causing "considerable injury" [3,57].
Young black cottonwood trees and seedlings are usually killed by fire regardless
of severity [24]. Severe fire kills or top-kills even older trees. In low- and moderate-severity fires older trees with
thick bark may not be top-killed [58,97]. In members of the Populus genus
stem bark remains thin for longer than in other trees [41]. Though old trees have increased fire resistance due to
thicker, furrowed bark, they have higher fuel loading and more heartrot,
which can increase fire severity [49]. Trunks that are not top-killed may
be more susceptible to Cytospora spp., and other fungal pathogens; this was observed
near D'Arcy in southern British
Columbia [34].

Black cottonwood sprouts from stumps,
charred boles, root crowns, or lateral roots following fire [24,28,58,97,109] and
because of this has been referred to as a fire "endurer" rather than
"resister" [3]. Fire-induced sprouting is more common in the Tacamahaca
section than in the Aigeiros section. Rates of sprouting are highest
if fire occurs when
cottonwoods are dormant [49]; this time also has the highest
probability of fire, with late summer and fall, or late winter (in low snow
years) most common [58]. In general older trees sprout less than
young trees [49], and sprout survival is highest when the water
table is close to the surface [58]. In 1986, Coates and
Haeussler [28] stated that there was little information regarding black
cottonwood sprout vigor
after fire, or impact of fire severity on sprouting potential. Though this is
still at least partially true, a study of clonal reproduction after fire in
Alberta by Gom and Rood [49] provides much useful data that is summarized in
the "Fire Effects" section of this species summary.

Black cottonwood is not only a fire "endurer" but also a fire
"invader." Fire can improve seedling establishment by increasing light
penetration and exposing mineral soil to allow seedling
establishment if moisture is available [3,24]. Increases in light
penetration following fire also aid establishment [24].

Black cottonwood seedlings have been observed 1 year after
stand-replacing fire in upland ponderosa pine/ Rocky Mountain Douglas-fir
habitat on the Bitterroot National Forest, Montana. The seedlings
grew in cavities in mineral soil after the root systems of large
trees had burned [131]. A study of seedling establishment (artificially seeded)
of balsam poplar after experimental fires in a black spruce habitat demonstrated
the dependency of the species on mineral soil exposure for germination and
survival. Fire was prescribed on 1 m2 plots.
On moderately burned plots 17 black cottonwood germinated, 1 survived 1 year, and 0 survived 3
years. On heavily burned plots 71 germinated, 39 survived 1 year, and 39
survived 3 years [158].

Fire is infrequent on recently formed gravel bars, but when it does occur, damage to
cottonwoods is greatest because their root systems have not developed [58].
FIRE REGIMES: Historic FIRE REGIMES have not been explicitly studied in black
cottonwood communities [10]. Because of high moisture content and rapid decomposition of litter in riparian forests, historical fire frequency in black cottonwood communities was probably less than in adjacent upland areas. However, wind-driven fires beginning in upland communities may spread to adjacent riparian forests, particularly when fuel accumulation on upland sites has increased as a result of fire exclusion [132]. Arno [10] states that black cottonwood forests along
major rivers of the Pacific Northwest likely burned frequently, as they were
historically surrounded by communities characterized by high fire frequency,
such as ponderosa pine savannas or sagebrush steppes. Fires could have easily spread from adjacent communities, particularly prior to widespread livestock grazing and irrigation, when dry grassy fuels were more continuous than they are currently
[10]. When fires do occur in black cottonwood communities, they are most severe in old stands with heavy fuel accumulations [49,132].

FIRE REGIMES for plant
communities and ecosystems in which black cottonwood is dominant are summarized
below. For further information regarding FIRE REGIMES and fire ecology of
communities and ecosystems where black cottonwood is found, see the "Fire
Ecology and Adaptations" section of the FEIS species summary for the plant
community or ecosystem dominants listed below.
Community or EcosystemDominant Species Fire Return Interval Range (years)grand firAbies grandis 35-200 [9]sagebrush steppeArtemisia tridentata/Pseudoroegneria spicata 20-70 Rocky Mountain juniperJuniperus scopulorum 104]western larchLarix occidentalis 25-100 Engelmann spruce-subalpine firPicea engelmannii-Abies lasiocarpa 35 to > 200 blue spruce*P. pungens 35-200 [9]Rocky Mountain lodgepole pine*Pinus contorta var. latifolia 25-300+ [8,9,118]western white pine*P. monticola 50-200 interior ponderosa pine*P. ponderosa var. scopulorum 2-10 [9]eastern cottonwoodPopulus deltoides 104]quaking aspen (west of the Great Plains)P. tremuloides 7-120 [9,53,96]Rocky Mountain Douglas-fir*Pseudotsuga menziesii var. glauca 25-100 [9]coastal Douglas-fir*P. menziesii var. menziesii 40-240 [9,100,116]western redcedar-western hemlockThuja plicata-Tsuga heterophylla > 200 [9]western hemlock-Sitka spruceTsuga heterophylla-Picea sitchensis > 200 [9,107]elm-ash-cottonwoodUlmus-Fraxinus-Populus spp. 39,154]

*fire return interval varies widely; trends in variation are noted in the species summary

More info on this topic.

More info for the terms: bog, climax, fern, hardwood, lichens, presence, succession

Black cottonwood is a pioneer and early seral species [28,41,57,58]. It and
other members of the Populus genus are some of the fastest growing temperate trees, an
adaptation useful for pioneering disturbed sites [41,57]. Any activity that exposes moist, mineral soil
in full sunlight creates a
favorable habitat for black cottonwood seedlings, particularly when seed trees are nearby
[28,58].  Black cottonwood is very shade intolerant [2,57,70]. The species can tolerate flooding and
sediment deposition; when young stems are covered by sediment during floods, sprouts grow from the
stem towards the current [2].

In wet
climates in forest clearings on non-alluvial sites black cottonwood is a common pioneer, but these
stands are generally small and soon overtaken by secondary succession conifers
such as Douglas-fir, western hemlock, western redcedar, Sitka spruce, Engelmann
spruce, white spruce, or grand fir. Similarly, black cottonwood, in moist
climates like that of the Pacific Northwest, colonizes agricultural clearings
where mineral soil is exposed and light penetration is high [19].

In southeastern Alaska, stages of community development
include pioneer, mid-successional willow-alder, and climax white spruce-western hemlock communities.
The pioneer community includes mosses and lichens (Rhacomitrium and Sterocaulon)
with mountainavens (Dryas spp.). The mid-successional willow-alder stage
includes Sitka alder, black cottonwood, Sitka
willow (Salix sitchensis), and Alaska bog willow (S. fuscescens).
Following the willow-alder stage, in the absence of
disturbance, white spruce and western hemlock eventually become dominant [6]. In a generalized model of forest succession following
fire in Alaska, Viereck [153] stated that balsam poplar and black cottonwood
were not "climax" species but were invaders, along with quaking
aspen,
after fires on relatively warm sites. Stands 70
to 80 years after fire consist "of white spruce and hardwood trees without a
closed overstory" [155].

On the Hoh River of the Olympic Mountains in Washington,
5 successional
stages are defined with respect to site age. Red alder and Scouler's willow are
dominant on the newest gravel bars, red alder alone dominates 80- to
100-year-old floodplains, an Engelmann spruce-bigleaf maple-black cottonwood
association is present on "1st terraces" that are approximately 400
years old, Sitka spruce and western hemlock dominate on "2nd
terraces" approximately 750 years old, and western hemlock is the dominant on
"3rd terraces" [44].

On the McKenzie River of Oregon, 3 early distinct
types of early successional vegetation were identified: black cottonwood communities, red alder communities,
and willow communities. In the absence of fire or flooding the black cottonwood
stage is succeeded by a western hemlock/western sword fern/ Oregon oxalis climax; in the presence of fire, the black cottonwood stage
is followed by a Douglas-fir/ beaked hazelnut (Corylus cornuta)/ western
sword fern community [64].

In black
cottonwood habitat types of southern and eastern Idaho, black cottonwood
establishes on recent gravel bars and remains dominant if there is continual
flooding and sediment deposition. Without this disturbance the community is
gradually replaced by Douglas-fir, Engelmann spruce, subalpine fir, or Rocky Mountain
juniper, but occasionally yellow willow or Geyer's willow (Salix geyeriana) will become dominant
[58]. Similar succession has been described in California, where it was
found that flood control leads to conifer types in California [70].

In the Swan Valley of western Montana, on wet portions of grand fir habitat
types, paper birch (Betula papyrifera) and black cottonwood pioneer clearcuts or seed-tree cuts where
mineral soil has been exposed; after these partially develop, Douglas-fir, grand
fir, western white pine (Pinus monticola), and spruce establish [7]. In Glacier National Park, as well as Oregon, Washington, and British Columbia,
black cottonwood is a common, though often short-lived component of early to mid-seral successional stages in western redcedar-western hemlock forests [55]

More info for the terms: density, fresh, natural

Breeding system: Flowers are unisexual and all members of the genus are dioecious
[16,41,60], though a small number of hermaphroditic or male flowers
have been observed on female trees in black cottonwood [139]. In some black
cottonwood populations sex
ratio is skewed, with male trees dominant on
warm, dry sites. In other populations the relationship between site and sex
ratio is apparently random [19].

Pollination: Black cottonwood is wind pollinated [41]. 

Seed production: Black cottonwood is typically produces seed after
7 to 10 years of age [19,57]. Seed production is "copious" [2], with about 30 to 50 seeds per capsule
[16]. Seed production is consistent, with large crops every year [57,126].

Seed dispersal: Seeds are lightweight; this characteristic, as well as
the
"cotton" from the seed pod, allow seeds to be carried by water or wind [57]. These are the general means of dispersal for all cottonwoods; seeds
travel "several hundred meters", in some cases up to
"several kilometers" (distances are estimates). Seed dispersal occurs when river flows begin to decline
after spring peak flows, sometimes as late as mid-summer. If flows are too high
seeds may be carried for so long that they lose viability before they reach
a favorable microsite [19].

Seed banking: As is common in plants that colonize disturbed habitats,
initial viability is high, but propagules are short-lived [2,57]. Seed
viability under natural conditions is estimated to be
1 to 2 weeks, and once a seed is wetted it needs to be deposited within 2 to 3
days to establish [19].

Germination: When moist mineral soil is exposed
germination rates are high, particularly when moist conditions persist for a
month after seed deposition [57]. The process of germination is
about 24 hours long. The
high initial mortality of seedlings  is "clearly a limiting factor in
the life cycle of cottonwoods" [19].

Seedling establishment/growth: Seedling mortality is very
high because of specific moisture requirements after germination; root growth in members of the
Populus genus during
the first 12 hours after germination is suppressed by low moisture [113].
Mortality in seedlings most commonly arises when root growth rates are
not as fast as the recession of the water table [57]. Root growth rates
for black cottonwood seedlings are some of the highest among cottonwoods: up to
0.48 inch per day (12 mm/day) [19]. Thus moisture
conditions in the 1st month of establishment are a defining factor in survival
[126]. The
rate of root development is much greater than that of the shoot in cottonwoods;
after 46 days of growth a group of balsam poplar × eastern cottonwood hybrid
seedlings had a mean leaf area of 0.16 inch2 (1 cm2) and a
root system that was 7 inches (17 cm) in length (in a "simulated riparian
environment") [113]. Seedling density on new point bars can range from 2 to 40/foot2
(23- 460/m2). The seeds have little endosperm: optimal
sunlight and moisture are required for carbohydrate synthesis early in establishment,
and, for this reason, seedling establishment in existing vegetation is very low. Though floods often distribute seeds widely, few seedlings survive where vegetation is developed [121]. Seedlings are able to withstand inundation and sediment deposition; this
process aids cottonwood establishment as it removes possible competitors [19]. Because of differential soil
moisture conditions, "banding" of seedlings with respect to elevation rather than
distance from the river has been observed at Oldman River near Lethbridge,
Alberta. Following flood on the Oldman River, seedling growth was rapid.
Mean height was 0.8 inch (2 cm) with a range of 0 to 6 inches (15 cm) after 1 growing
season. After
2 growing seasons mean height was 3 inches (8 cm), with a maximum of 20 inches (51 cm) [121].  Black cottonwoods
that had established from seed near Camas, Washington grew in 9 years to 50 feet
(15 m) tall and 7 inches (17 cm) in diameter [11]. At another site in Washington average height in a pure stand of 4-year-old
trees was 33 feet (10 m) [57]. Though floods can initiate seedling establishment, ice jams
and turbulent
melting associated with spring runoff often scour seedlings established in
preceding years [121].

Cottonwood establishment by seed is episodic, depending on seed viability at time
of deposition (which depends on the magnitude of flows) and on moisture
conditions in the first month of growth [89]. Suitable conditions for seedling
establishment sometimes occur (erratically) in approximately 5 to 10 year
intervals [19]. Scott and others [128] studied patterns of cottonwood recruitment with respect
to different fluvial processes. They found that studying recruitment is
often biased by dating trees from growth rings at ground surface; this method
was found to underestimate by an average of 5.1
years (range was 0 to 34 years) because of sediment deposition after establishment.
Because of light requirements seedling establishment seldom occurs
on sites where cottonwood is already dominant and other vegetation is established [19]. Most regeneration in
established forests is by
"root suckers" or coppice sprouts. On "older islands" studied in southern British Columbia,
root suckers were the most common means of regeneration. On more recently exposed
sites seedlings were 95% of dense stands; the other 5% were derived from twigs [47].

Scott and
others [128] summarized how different geomorphic processes influence the type
of cottonwood stand that will be established: 

Fluvial processFlowLandformCommunity patternsNarrowingone to several years of flow less than that necessary to
mobilize channel bed channel bedvariable spatial patterns; usually not even-aged standsMeanderingfrequent moderate flowspoint barsmoderate number of even-aged stands, arranged in narrow,
arcuate bands; strong left-bank, right-bank asymmetry in ages based on
meander pattern; flood training or stems commonFlood depositioninfrequent high flowsflood depositssmall number of linear, even-aged stands; flood training of
stems rare

Asexual regeneration: Cottonwood recruitment is commonly
asexual, via root suckering [2,19,41,57], coppice sprouting [57,59], or cladoptosis (the physiological abscission of
twigs with leaves still attached) [19,47]. The means of
regeneration depends site characteristics and whether or not
black cottonwood is already present.

Cladoptosis is an important means of regeneration of black cottonwood on gravel
bars [36]. This
means of asexual reproduction is most viable in moist climates; because of hot,
dry summers it apparently does not occur in Alberta [50]. In laboratory conditions up to 95% of
freshly collected, abscised twigs produced roots (the greatest rooting was in twigs
shed in October) [47]. Branches of black
cottonwood that are broken off often grow when deposited in fresh alluvium; this
was observed following the Mt. St. Helens mudflows [1].

Rood and others [120] studied origins of cottonwood saplings
along the Oldman River in Alberta. Where sprouting occurred it was most
often the result of flood damage. When floods removed stems, root suckering was
induced, and when floods buried stems, shoot sprouting was induced [120]. Hansen and others [59] stated that the sprouting ability of black cottonwood is less than
that of narrowleaf cottonwood but greater than that of eastern cottonwood [59]; the findings of Rood and others
[120], given below, at least partially refute
that.

SpeciesSeedlings (%)Root suckers (%)Shoot suckers (%)nNarrowleaf cottonwood23.755.920.359Balsam poplar (includes some black cottonwood and hybrids)25.641.932.643Eastern cottonwood27.6072.476

Root suckering in narrowleaf, plains and balsam poplar (subspecies not
specified, but likely P. b. subsp. balsamifera) in pots was studied
by Schier and Campbell [124]. Results for balsam poplar are presented
below (n= 30 to 90):

 Clone 1Clone 2Root collection date9/410/7Mean age (years)8.5-# root segments3060Sucker emergence (days)3230Segments suckering (%)6090Suckers/segment16.913.2Segments with surface suckers (%)10093Surface suckers/segment4.96.0Height of tallest sucker (mm)-66

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More info for the terms: geophyte, phanerophyte

RAUNKIAER [114] LIFE FORM:

Phanerophyte

Geophyte

More info for the term: tree

Tree

Black cottonwood is classed as  very intolerant of shade. It grows best in full sunlight. On  moist lowland sites, it makes rapid initial growth and thereby  survives competition from slower growing associated species.

    Data from British Columbia indicate that black cottonwood trees  can take advantage of wide initial spacing (1); diameters of  trees and sets established at a 9.14-m (30-ft) spacing averaged  30 to 75 percent greater than those of plants established at a  1.82-m (6-ft) spacing (28,29). Results from a spacing trial in  Washington, however, indicate better height and diameter growth  at 3.7- by 3.7-m (12- by 12-ft) spacing than at 3.0- by 9.1-m  (10- by 30-ft) and 6.1- by 9.1-m (20- by 30-ft) spacings (10).  Black cottonwood responds well to thinning (29).

    In the past decade, most of the research on black cottonwood has  focused on use of the species in short-rotation, coppice systems  for fiber and energy. Spacings have varied from 0.3 by 0.3 m (1  by 1 ft) to 1.8 by 1.8 m (6 by 6 ft) and rotations or cutting  cycles of 2 to 8 years (8,11,12,14). Mean annual production has  ranged from about 2 to more than 16 mg/ha (1 to 7 tons/acre). The  most recent findings suggest that rotations longer than 4 years  (perhaps 8 or more) result in highest mean annual production  (11); with such rotations, spacings of 1.8 by 1.8 in (6 by 6 ft)  or wider may be used, provided that competition from grass and  weeds is controlled. Higher coppice yield was obtained in a mixed  planting of black cottonwood and red alder (a nitrogen-fixing  species) than from pure plantings of either species (2). A  subsequent study of the black cottonwood-alder mixture on a  better site showed no benefits after the second year, presumably  because cottonwood shaded and overtopped alder and thus impaired  nitrogen fixation (13).

Planted cuttings of black cottonwood root  very well; they produce deep and widespread root systems if  growth is not restricted by adverse soil conditions. Little  information on rooting has been collected in natural or seedling  stands.

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More info for the term: phenology

In poplars, shoot elongation continues after bud burst. Leaves mature and
expand throughout the growing season which is defined, at least partially, by photoperiod
[117].  All temperate members of the genus flower in the spring before
leaf growth initiation [41,57], as is typical of plants that depend on wind dispersal
[57]. Three or four weeks before flowers develop in the
spring, the following year's inflorescences develop at leaf nodes [16].

Seasonal development of black cottonwood has been
studied in detail in British Columbia, Yellowstone National Park, and northern
Idaho. Black cottonwood flowers in late March or early April
until late May in coastal British Columbia, though in the interior flowering may not
occur until the middle of June. Leaves appear after flowers. Fruit ripens about a month after flowers appear; seed dispersal occurs between
late April and July [57].

Phenology of black cottonwood was studied in
Yellowstone National Park (east of continental divide) [125]: 

 Bud burstLeaves fully grownFlowers startFlowers endFruit ripeLeaves start to color or witherLeaves begin to fallLeaves fallen and witheredAverage dateMay 14June 20May 11June 5July 2September 10September 23October 14Earliest dateApril 28June 10April 25April 10May 17July 23August 10October 5Latest dateMay 29July 12June 4July 12July 19September 19October 3October 22Standard error323107442Sample size1414101010141414
Northern Idaho phenology is described below (west of continental divide)
[125]:

 Bud burstLeaves fully grownFlowers startFlowers endFruit ripeSeed fall beginsLeaves start to color or witherLeaves begin to fallLeaves fallen and witheredAverage dateApril 30May 30May 19June 11August 14September 19September 15September 28October 14Earliest dateApril 20May 1April 1May 15June 25August 18August 20September 15October 2Latest dateMay 14July 13June 16July 2September 5October 21October 25October 10October 26Standard error (days)2543513522Sample size13131515145151614

Black cottonwood sprouts readily  from stumps, and in one study, satisfactory coppice reproduction  was obtained four times in 2-year cutting cycles (8). After  logging operations, black cottonwoods sometimes regenerate  naturally from rooting of partially buried fragments of branches  (9). Sprouting from roots has also been reported (23). The  species also has the unusual ability to abscise small shoots  complete with green leaves (6). These shoots drop to the ground  and may root where they fall or may be dispersed by water  transport. In some situations, abscission may be one means of  colonizing exposed sandbars.

    The species is easily reproduced by rooted and unrooted cuttings  (30). The cuttings are made in the dormant season and may be as  short as 15 cm (6 in). Most research and small-scale operational  plantings have been established with unrooted stem cuttings taken  from 1- and 2-year-old wood, I to 3 em (0.4 to 1.2 in) in  diameter at the small end and 40 to 60 cm (16 to 24 in) long.  Good results have also been obtained with branchwood cuttings, in  some instances collected from trees as old as 30 years (9).  Usually the cuttings are planted in the spring to a depth of 80  to 40 em (12 to 16 in). Best establishment and growth are  achieved when cuttings have healthy axillary buds, at least one  of which remains above ground after planting (22). Plantings of  very long cuttings (3 in or 10 ft or more in length) have  sometimes been used successfully to overcome problems of weed  competition or animal damage (29); in other cases, they have  failed, presumably because top growth and thus transpiration  stress outstripped root growth and the ability of the root system  to provide moisture during the dry summer. The proportion of  trees with poor form and the magnitude of crookedness are greater  in trees established with long cuttings than with short cuttings  (10). Height of trees established from cuttings has frequently  exceeded 1.5 in (5 ft) at the end of the first year and 6 in (20  ft) after 4 years (11). Height growth rates of cottonwood sprouts  have been even greater.

Moist seedbeds are essential for  high germination (23), and seedling survival depends on  continuously favorable conditions during the first month (25).  Wet bottom lands of rivers and major streams frequently provide  such conditions, particularly where bare soil has been exposed or  new soil laid down. Germination is epigeal. Black cottonwood  seedlings do not usually become established in abundance after  logging unless special measures are taken to prepare the bare,  moist seedbeds required for initial establishment (23). Where  seedlings become established in great numbers, they thin out  naturally by age 5 because the weaker seedlings of this  shade-intolerant species are suppressed (23).

The seed ripens and is  disseminated by late May to late June in Oregon and Washington,  but frequently not until mid-July in Idaho and Montana (23).  Abundant seed crops are usually produced every year. Attached to  its cotton, the seed is light and buoyant and can be transported  long distances by wind and water. Although highly viable,  longevity of black cottonwood seed under natural conditions may  be as short as 2 weeks to a month. There is some evidence,  however, to suggest a somewhat longer lifespan under apparently  adverse conditions. With proper drying and cold storage,  viability and capacity to germinate can be maintained for at  least 1 year (25).

Black cottonwood is normally  dioecious; male and female catkins are borne on separate trees.  The species reaches flowering age at about 10 years (25). Flowers  may appear in early March to late May in Washington and Oregon,  and sometimes as late as mid-June in northern and interior  British Columbia, Idaho, and Montana. Staminate catkins contain  30 to 60 stamens, elongate to 2 to 3 cm (0.8 to 1.2 in), and are   deciduous. Pistillate catkins at maturity are 8 to 20 ern (3.2 to  8 in) long with rotund-ovate, three carpellate subsessile fruits  5 to 8 min (0.20 to 0.32 in) long. Each capsule contains many  minute seeds with long, white cottony hairs.

Black cottonwood may attain pulpwood  size in 10 to 15 years, and saw log-size trees have been observed  in plantations less than 25 years old in British Columbia and  Washington. For example, dominant and codominant trees of 17 cm  (6.7 in) in d.b.h. and 14.8 m (48.5 ft) in height at 9 years have  been reported for a good moist site (26). In the lower Fraser  River Valley of British Columbia, planted black cottonwoods   averaged 20 cm (8 in) in d.b.h. and 16.8 m (55 ft) in height at  10 years, and some individual trees were more than 30 ern (12 in)  in d.b.h. and 21.3 m (70 ft) in height (29). Growth is  considerably less in northerly and interior locations. In the  Willamette Valley of Oregon, black cottonwood matures in 60 years  or less (23), but studies in British Columbia show that the  species grows well for as long as 200 years (33). Exceptional  trees have attained 180 to 300 cm. (72 to 120 in) in d.b.h. and  more than 60 m (200 ft) in height (7,35).

    Growth and yield data for natural black cottonwood stands are  available for the Quesnel region and Skeena River Valley of  British Columbia (33). Other Canadian studies have indicated that  three site quality classes developed for German poplar (16) are  satisfactory for black cottonwood stands in British Columbia  (30). The Forest Inventory Branch of the British Columbia Forest  Service has collected much growth and yield data on natural  stands of black cottonwood. Some of this information is  summarized in table 1. These data clearly indicate that  differences in yield among site classes are large; the mean  annual production of site I is nearly twice that of site II, and  more than three times that of site III.

        Site  class and stand age  Average  d.b.h.  Stocking  Height¹  Net  volume  Maximum  mean annual increment  Age of  culmination          yr  cm  trees/ha  m  m³/ha  m³/ha  yr    I,  112  46  294  41.1  302.3  5.5  62    II,  101  33  415  29.6  219.9  2.8  78    II,  87  28  474  21.3  122.8  1.7  96      yr  in  trees/acre  ft  ft³/acre  ft³/acre  yr    I,  112  18  119  135  4,319  79  62    II,  101  13  168  97  3,141  40  78    III,  87  11  192  70  1,755  24  96    ¹Dominants and  codominants.       

    Yields from black cottonwood plantations are expected to be much  higher than yields from natural stands. Data from three  plantations in the lower Fraser River Valley indicate mean annual  increments ranging from 10.5 to 15.4 m³/ha (150 to 220 ft³/acre)  per year (28). A plantation established on a deep alluvial soil  in coastal Washington has produced more than 500 m³/ha  (7,242 ft³/acre) in 24 years (19). Dominant trees range from  35 to 37 m (115 to 122 ft) in height and 33 to 41 cm (13 to 16  in) in d.b.h.

Population Differences    Black cottonwood exhibits considerable variation throughout its  range. Photoperiodic studies conducted under uniform  environmental conditions in Massachusetts have shown that  northern provenances cease growth earlier than southern  provenances (21). Moreover, cessation of growth among clones from  the same latitude was related to length of the growing season  (frost-free days) at places of origin (that is, elevation).   Another study (18) conducted with clones indicates that several  aspects of shoot growth are under genetic control: date of  flushing, amount of early growth, growth rate in midseason, date  of cessation, and average length of internode. A more recent  study (36) demonstrated a large range of variation in leaf,  branch, and phenology characters in 50 clones (five each from 10  natural populations growing in drainages west of the Cascade  Range). Population means for several characters varied clinally  with source latitude, longitude, and/or elevation. In general,  southwestern clones developed smaller leaves, had more numerous  and more erect branches, and continued growth later in the fall  than northeastern clones. Experiments in pots and flats have  shown that some clones of black cottonwood grow taller in the  presence of another clone than when planted by themselves (32).

    Hybrids    Black cottonwood hybridizes freely with balsam poplar (Populus  balsamifera) where the ranges of the two species overlap  (35). Another natural hybrid, the Parry cottonwood, resulting  from crosses with P. fremontii is native to  California. A hybrid (Populus x generosa Henry)  between P. angulata (now considered either a  variety or cultivar of P. deltoides) and R  trichocarpa was developed in England (24). Also, P.  maximowiczii x trichocarpa and P. deltoides x P.  trichocarpa hybrids have been planted in the northeastern  United States. Recent work in which P. trichocarpa  was crossed with superior selections of P. deltoides from  the southern United States has produced hybrids of markedly  superior growth performance (12,31).

Canada

Rounded National Status Rank: NNR - Unranked

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: T5 - Secure

Reasons: Populus balsamifera spp. trichocarpa, like other P. balsamifera, is found in moist to wet sites at low to medium elevations (sea-level to 4500 feet). It can form dense stands on stream islands and along floodplains of major rivers (WSDOT 2001).

Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status, such as state noxious status and wetland indicator values.

More info for the terms: cover, density, frequency, shrub, tree

The exact amount of decline in riparian cottonwood stands is unknown. In the
Southwest, an estimated 70 to 95% of riparian vegetation has been lost or
disturbed; in the Sacramento Valley of California the area of riparian
forests has been reduced by 98.5% since 1850; in Idaho, Wyoming, Montana, and Canada, less has been lost. Causes of decline of
riparian cottonwood stands in western North America were outlined by Braatne and
others [19] as follows:

FactorImpacts1. Livestock grazingconsumption and trampling of seedlings - death of older trees
causes gradual decline 2. Water diversiondrought stress3. Domestic settlementclearing area for home development4. Exotic plantssaltcedar (Tamarix subsp.) and Russian-olive (Elaeagnus
angustifolia), among others, can reduce recruitment5. Stream reservoirsmany stands were lost when dams were built in the West6. Channelizationthis reduces meandering, a process critical to cottonwood
establishment7. Agricultural clearingthis was greatest prior to 1950, there has likely been
little net change since then8. Gravel mining excavated areas and associated infrastructure require
forest clearing, but cottonwoods often regenerate asexually9. Direct harvestingduring early European-American settlement the wood was used
more than it is currently10. Beaverspopulations of beavers are unnaturally high in many areas
due to a lack of predators
Rood and Mahoney [122] examined decline
of cottonwood forests in southern Alberta. They listed many of the
above-mentioned activities. Causes of decline were, from largest to smallest
impact, 1) livestock grazing, 2) agricultural clearing,
3) water diversion, 4) domestic settlement, 5) stream reservoirs, 6) increase
in beaver population,
7) gravel mining, 8) direct harvesting, 9) channelization, and 10) herbicide
spraying.

Major causes of decline of black cottonwood stands in
eastern Oregon include: conversion of stands for pasture, farmland, or
urbanization, conversion of streams from multiple to single channel systems,
restriction of lateral movement of streams across floodplains, and control of
flooding with dams. Overbrowsing by livestock, elk, and deer, reduced fire
frequency, and logging for firewood, lumber, and pulp have also had impacts
[31].

Livestock management: Though they require flooding disturbance for establishment,
black cottonwood seedlings are generally not tolerant of much grazing disturbance. In
southern Alberta, stress from livestock use, including foraging and trampling, is "the greatest overall impact on riparian
cottonwood" stands according to Rood and others [121]. In the
Wallowa Mountains of eastern Oregon, an exclosure study showed that livestock
use slowed the development of black cottonwood stands and delayed succession
from shrub-dominated to black cottonwood dominated communities [78]. Gravel bar vegetation surveys in the Catherine Creek watershed
of eastern Oregon also highlighted the sensitivity of black cottonwood to
livestock pressure. In exclosure plots mean height increased from 6 to 40 inches (15
to 101 cm) in
10 years; on plots with grazing (1.3- 1.8 ha/AUM), mean height increase was only
from 5 to 10 inches (12-26 cm) in the same time period. During this study
shrub (mountain alder, Bebb willow, and Missouri River willow (Salix
eriocephala)) density increased
significantly (p<0.01) on sites excluded from grazing, but the density of
black cottonwood was not significantly different between grazed and ungrazed
sites [51]. Management has
sought to control livestock foraging and trampling effects on black cottonwood
via short-rotation grazing and exclosure; this allows young trees approximately
5 years to establish [19]. 

Prolonged heavy grazing of black
cottonwood community types can cause decline in shrub canopy cover and thus big
game use of the site. Shrub cover can sometimes be restored with a "dramatic
change" in management including elimination of grazing. The success of this depends most heavily on the level of the
water table. Whether or not the goal is to restore shrub cover, early
season rest from grazing is beneficial for forage production alone [58].

Timber management: Though black cottonwood has beneficial effects on bank
stability, black cottonwood can have detrimental competitive
effects on more economically valuable trees. This effect is greatest during the
first 5 years after clearing; self-thinning at this point reduces black
cottonwood abundance but many persist throughout rotation times [57]. Logging mature cottonwood produces abundant
rapidly growing stump sprouts. Sprouts grow whenever the tree is cut, but cutting
in November through February produces the most.  Even repeated cutting (up
to 5 times in 10 years) does not harm the ability to sprout from stumps. In
addition twigs or roots that are covered with soil during logging often take
root.  When mature trees are still present, seeding is rapid.
Because of these characteristics manual treatment is not effective in reducing
density or cover of black cottonwood [28].

To increase habitat for
nesting birds, Habitat management plans are best developed for each individual
species, but some general considerations include: within a 1,000 acre (400 ha) area about 50 to
100 acres (20 to 40 ha) with an old-growth structure of ponderosa pine, western larch, or
black cottonwood should meet most nesting needs. This 50- to 100-acre area is
most effective if scattered
throughout the larger area rather than isolated, and in the remaining 900 acres (360 ha) snags
are retained. Also suggested for bird habitat maintenance
is that the collection of ponderosa pine, western larch, or black cottonwood for
firewood be discouraged, particularly collection of snags greater than 15 inches (38 cm) in
diameter
[94].
Watercourse damming and water diversion: Often listed as a
major detriment to cottonwoods, damming and water diversion have a multi-faceted
impact on establishment, growth, and mortality. These factors
were summarized by Rood and Mahoney [122] as follows: 

Possible cause of declineEffectsHydrologic changesA. Reduced water availabilityDiversion of water offstream or well pumping
creates a water deficit, resulting in drought stress, slow growth, and
increased mortalityB. Reduced floodingSpring flooding is essential to create moist
seedbeds for seedling establishmentC. Stabilized flowsDynamic flows are essential for seedling
establishmentGeomorphic changesA. Reduced meandering and channelizationWith reduced flooding, channel migration is
reduced and suitable seedbeds are reduced
Impacts of watercourse damming on cottonwoods
are generally negative, but also dependent on the species present, as reported by Rood and Mahoney [122]:

RiverState/provinceSpeciesEffectsReferenceMissouriNDplains cottonwoodReduced tree growth and less seedling establishment[76]severalAZFremont cottonwood, narrowleaf cottonwoodReduced forest abundance[23]ColoradoCAFremont cottonwoodReduced forest abundance, absence of seedlings[102]South PlatteCOplains cottonwoodReduced forest abundance[30]MissouriMTplains cottonwoodReduced forest abundance, absence of seedlings[103]OwensCAFremont cottonwoodReduced forest abundance[22]Rush CreekCAbalsam poplarReduced tree abundance[141]SacramentoCAFremont cottonwoodFewer seedlings[142]SaltAZFremont cottonwoodConditions unsuitable for seedling establishment[43]MilkMT, ABplains cottonwoodReduced forest abundance, fewer saplings[20]BighornWYplains cottonwoodReduced forest abundance[5]St. Mary, Waterton, BellyABplains cottonwood, balsam poplar, narrowleaf cottonwoodReduced forest abundance[119]Rio GrandeNMFremont cottonwoodAbsence of seedlings[72]Bishop CreekCAFremont cottonwood, balsam poplarSmaller leaves, reduced transpiration and water potential[150]ArkansasCOplains cottonwoodReduced forest abundance[133]
The effects of altered flood magnitude, frequency, and
duration on the establishment and success of black cottonwood are thought to be
less severe than those effects on other cottonwoods [83]. This is because black
cottonwood is adapted to flow regimes of smaller streams with more variable
flood magnitude and duration than large rivers. Stromberg and Patten [143] noted
"subtle" effects of diversion on black cottonwood in the eastern
Sierra Nevada, California. On Bishop Creek, where water diversion is nearly
complete in normal and dry winters, black cottonwood had higher mortality (and
thus lower age and size), lower
density, and lower canopy foliage density than on Pine Creek, a similar size
watershed with no diversion. Means (standard errors in parentheses) from the two
watersheds are presented below [143]: 

SiteElevation (m)Canopy foliage density1Tree mortality2 (%)Tree density (#/ 0.1 ha)Juvenile density3 (#/ 0.1 ha)Bishop 22,0201.73 (0.16)272898Bishop 31,8000.51 (0.12)143393Bishop 41,4700.35 (0.12)33642Pine 22,1002.52 (0.25)941199Pine 31,8502.14 (0.19)045170Pine 41,5803.13 (0.37)1138125

1 Leaf area index (m2/ m2)

2 Dead trees as a percentage of the total

3 Juveniles are plants

Chemical treatments: Black cottonwood is
"extremely sensitive" to glyphosate. In southern Alberta this
herbicide and picloram are believed to have caused unintended mortality in even
large trees [122]. The 2,4-D ester can damage
the canopy but does not cause much mortality [28]. High black cottonwood
mortality was observed following summer and fall
applications of glyphosate. A mid-May spot treatment with hexazinone produced
80% to 95% defoliation and little sprouting in the Nelson Forest region of
British Columbia. Broadcast treatments with 2,4-D amine have been
observed to cause moderate or severe damage [57]. Balsam poplar in
Alberta were susceptible to metsulfuron and 2,4-D, alone or in combination [18].

Disease and Black cottonwood is susceptible to Cytospora
canker, particularly in fire-damaged stands or in young trees or
cuttings in nurseries. Wood-decaying fungi also grow on black cottonwood; the most significant parasites of this sort include Polyporus
delectans and Philota destruens [117]. Young seedlings
are particularly susceptible to pathogenic fungal infection [113]. Trees, particularly young saplings, may be injured or
killed by late frost either directly or indirectly via increased susceptibility
to fungal decay. High winds sometimes cause damage on sites where adjacent
vegetation is much shorter [35], and scouring by ice during spring runoff
sometimes kills or induces sprouting from young trees [19].

Contact your local Natural Resources Conservation Service (formerly Soil Conservation Service) office for more information. Look in the phone book under ”United States Government.” The Natural Resources Conservation Service will be listed under the subheading “Department of Agriculture.”

In urban sites, the aggressive root systems of black cottonwood can invade and damage drainage systems and also may heavily draw available moisture from gardens and building foundations, especially in clay soil. Root suckers also may be considered a maintenance problem, and the profuse production of cottony seed from female plants can be a minor nuisance. The shallow root system of black cottonwood, especially on wet soils, make the species susceptible to damage from ice storms, heavy snow, and wind. Unseasonably early or late frosts may damage saplings, but in dormancy, it is one of the most frost-resistant trees in the northwestern USA.

Black cottonwood is susceptible to fire damage because of its thin bark and shallow root system. Seedlings and saplings are usually killed by fire of any intensity, and all trees may killed by high-intensity fire. Even relatively cool fires may wound older trees and open the way to heartwood decay. Repeated fire at short intervals may permanently exclude black cottonwood. Even so, post-fire regeneration may be effective and rapid in black cottonwood. Thickened bark on lower portions of the trunk after 10-20 years affords better fire protection, and moist soil contributes to the survival of underground parts. Trees can quickly sprout from the stump and roots following top-kill or damage by fire. Abundant production of seeds and their wide dispersal enable black cottonwood to rapidly colonize large areas of moist soil after burns, which provide ideal conditions of maximum light and bare mineral soil.

Collect seeds for propagation as capsules begin to open (late May to mid July). Place in paper bags and allow them to finish opening in warm area. They need to be sown within a few days of ripening; otherwise they may be kept viable for up to a year by drying and storing cold in an air-tight container. In a cold frame, sow on the surface or lightly cover the seeds. Plant into permanent positions either in late summer or the following spring, depending on growth of the young plants.

Cuttings of twigs of the current season's growth, 20-45 cm long and 1-3 cm diameter, taken during the dormant season and with healthy axillary buds, can be placed in a sheltered outdoor bed or directly into permanent positions. Plant with one bud above the surface. Cuttings grown in a mist-propagator also root easily. Nursery- or container-grown seedlings and rooted cuttings establish easily and grow rapidly on moist well-drained soils in full sun. Live stakes should be 3.5 cm diameter and 1.2 m long, stuck directly into ground on-site.

Black cottonwood has been planted as windbreaks and shelterbelts  in conjunction with irrigated agriculture in the Columbia River  basin.

    The wood of black cottonwood is similar to that of other  cottonwoods (20,34). It has light color, straight grain, fine,  even texture, and is light in weight. It dries easily, is  moderately stable in use, and, although not strong, is tough for  its weight.

    Black cottonwood has short, fine fibers and is used to produce  pulp for high-grade book and magazine papers. The species peels  easily, and its veneer is used as core and cross-banding stock in  plywood and in baskets and crates. The light weight, good nailing  characteristics, and light color of the lumber are ideal for  manufacture of pallets, boxes, and crates. The lumber is also  used in concealed parts of furniture. Fiberboard and flakeboard  are made from black cottonwood. In early days, it was used for  cooperage.

Industry: Black cottonwood is a commercially valuable tree. Primary products include particle board, plywood, veneer, and lumber. The wood is light colored and light in weight; it is diffuse-porous (indistinct growth rings), with a fine, even texture. The light weight, good nailing characteristics, and light color of the lumber are ideal for manufacture of pallets, boxes, and crates. It also is used in concealed parts of furniture. The fibers are short and fine, making the wood useful in production of pulp for tissues and high-grade book and magazine paper.

Poplar hybrids, particularly Populus trichocarpa x P. deltoides, are currently the subject of much research into their genetics and physiology. These are extremely fast-growing and biomass-productive when grown as short-rotation coppice or single stems. On good sites, hybrid poplars grow faster than any other northern temperate region tree and hybrids are usually more widely adaptable than the parents. They are easily propagated from stem cuttings, but because of quick re-sprouting, replanting after harvesting may be unnecessary, especially for short harvest cycles. These trees have great potential for conservation and ornamental plantings, paper, and lumber and plywood. The wood is similar to that of native black cottonwood, and branches and tops left from pulp harvests can be converted to pelletized fuel for use in power stations and home heaters.

Wildlife: Black cottonwood provides food and cover for a variety of wildlife species, including deer, elk, and beaver. Large birds use the crowns for nesting sites and various animals rely on the trunk cavities, which commonly result from heart rot in most stands nearing maturity. The rotten trunks of black cottonwood provide an important wildlife habitat otherwise scarce, especially of the Cascades.

Ethnobotanic: Disinfectant properties of resin from buds were discovered by Native Americans, who used the resin to treat sore throats, coughs, lung pain, and rheumatism. It is still used in some modern natural health ointments. Soap was produced from the inner bark. The wood was used to make friction fire sets.

Conservation: Black cottonwood is a very fast-growing and potentially large tree, easy to establish, and useful for shade and ornament. Black cottonwood also has been planted as windbreaks and shelterbelts and it is commonly used for screening along motorways in Europe. The aggressive root systems of black cottonwood are effective soil stabilizers and make the species useful in restoration of riparian areas, where it also provides protection for the aquatic environment, especially in helping to maintain low water temperatures through shading. The high nitrate uptake and extensive rooting of these trees make them useful for buffer or "filter" planting along streams in agricultural areas.