Black cottonwood (Populus trichocarpa): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table.

At a glance

Item	What the source records
Scientific name	Populus trichocarpa Torr. & Gray, willow family (PLANTS lists it as Populus balsamifera subspecies trichocarpa)
Other names	Balsam cottonwood, western balsam poplar and California poplar (Silvics)
Native status, USDA PLANTS	Native in Alaska, Canada and the lower 48 states
Size, Silvics	The largest of the American poplars and the largest hardwood tree in western North America
Green weight of the wood, NRS-38	46 lb per cubic foot, without bark

Native range

The Silvics of North America handbook (Agriculture Handbook 654, volume 2, 1990) says black cottonwood grows primarily on moist sites west of the Rocky Mountains, with the best sites on the river-bottom lands west of the Cascade Range in the Pacific Northwest, where alluvial soils can carry pure stands. The range extends northeast from Kodiak Island along Cook Inlet to latitude 62 degrees 30 minutes north, then southeast in southeast Alaska and British Columbia to the forested areas of Washington and Oregon, and to the mountains in southern California and northern Baja California. Inland it is found generally on the west side of the Rocky Mountains in British Columbia, western Alberta, western Montana and northern Idaho, with scattered small populations in southeastern Alberta, eastern Montana, western North Dakota, western Wyoming, Utah and Nevada. The handbook says the tree is harvested for lumber, veneer and fiber products, and planted for shade and in windbreaks and shelterbelts, including with irrigated agriculture in the Columbia River basin.

Flowers and growth

Silvics describes black cottonwood as normally dioecious, with male and female catkins on separate trees, reaching flowering age at about 10 years. Flowers may appear from early March to late May in Washington and Oregon and as late as mid-June in northern and interior British Columbia, Idaho and Montana. Female catkins at maturity are 8 to 20 cm (3.2 to 8 in) long, and each capsule contains many minute seeds with long white cottony hairs. On growth, the handbook says black cottonwood may reach pulpwood size at 10 to 15 years of age and sawlog-size trees have been seen in plantations under 25 years old in British Columbia and Washington. It gives dominant and codominant trees of 17 cm (6.7 in) in diameter and 14.8 m (48.5 ft) tall at age 9 on a good moist site, and planted trees in the lower Fraser River Valley averaging 20 cm (8 in) in diameter and 16.8 m (55 ft) tall at age 10. Growth is considerably less in northerly and interior locations.

Roots

The handbook says planted cuttings root very well and produce deep and widespread root systems if growth is not restricted by adverse soil conditions, and that little information on rooting has been collected in natural or seedling stands.

Wood

The Wood Handbook (FPL-GTR-282, 2021) says the heartwood of cottonwood is grayish white to light brown with whitish sapwood, comparatively uniform texture and generally straight grain, and that most strength properties of black cottonwood are slightly lower than those of eastern cottonwood. It describes eastern cottonwood as moderately low in bending and compressive strength, moderately stiff, moderately soft and moderately low in shock resistance, with moderately high shrinkage in both eastern and black cottonwood, and notes that some cottonwood is difficult to work with tools because of a fuzzy surface mainly resulting from tension wood. Silvics adds that the wood is light in colour, light in weight, dries easily and is moderately stable in use, that short fine fibers make pulp for high-grade book and magazine papers, and that the veneer is used as core and cross-banding in plywood and in baskets and crates, with lumber used for pallets, boxes and crates.

Wood Handbook Table 5-3b	Specific gravity	Modulus of rupture (lbf per square inch)	Side hardness (lbf)
Green	0.31	4,900	250
At 12% moisture content	0.35	8,500	350

The Wood Handbook states that specific gravity is based on oven-dry weight and the volume when green or at 12% moisture content. The green weight of the wood without bark is in the NRS-38 table, the same figure used in the log weight calculator.

Pests, diseases and damage the handbook names

Silvics (1990) says that although several insects attack black cottonwood, none has been reported as a pest of economic significance, and names these agents by the names it used.

Insects. Tent caterpillars, two sawflies, the satin moth and a leaf blotch miner as foliar feeders; oystershell scale, reported as frequently killing twigs and branches and sometimes a whole tree; a bud midge on stressed trees; a bark moth that mines the cambium; and two borers, a flatheaded borer and the poplar-and-willow borer, which the handbook calls a European insect established across much of the range. Other flatheaded and roundheaded borers and ambrosia beetles are known to destroy the wood.
Decay fungi. At least 70 fungal species cause decay in cottonwood, but only six cause significant losses in British Columbia, and two of those (Spongipellis delectans and Pholiota destruens) cause 92 percent of the loss.
Leaf rust and leaf diseases. Melampsora leaf rust in young plantations, which limits photosynthesis and causes early leaf fall, with severe infections seen where clones from drier areas were planted in western Washington, in one instance killing the clones. Leaf-spot (Venturia populina) and yellow-leaf blister (Taphrina populisalicis) are also named.
Cankers. Cytospora canker, widespread under forest conditions but rarely significant in vigorous stands, and stem cankers caused by Dothichiza, Fusarium, Hypoxylon mammatum, Nectria galligena and Septoria musiva. The handbook says none appear to be of great significance in management and that a severe bacterial canker has reportedly limited planting in Europe.
Wet wood. A condition that leads to wood collapse during drying.
Weather, fire and animals. Early or late frosts injure saplings, frost cracks lower wood quality and provide an entrance for decay fungi, ice and heavy snow cause breakage, and the species is highly susceptible to fire. Meadow voles, rabbits and hares, beavers, elk, deer and slugs damage young plantings.

The guide on reporting a pest in the United States and the Canada reporting page give the offices that take sightings of regulated pests. Who may apply pesticides is in pesticide licences by country.