It's summer, and you might have noticed the fluffy seeds of cottonwood floating around your local park, looking almost like a layer of fresh snow. Cottonwoods are our #10 reason the Love the Lower Columbia.
So why do we love these trees in particular?
Black cottonwood (Populus trichocarpa) has a lot of remarkable features. It is the most massive broad-leaved deciduous tree in the Pacific Northwest, and It can grow to over 200 feet tall with a trunk that reaches 7 feet in diameter. Individual trees can live to be 200 years old.
Black cottonwood is found growing west of the Rockies and grows best on deep, moist alluvial soils. It can often be found growing on freshly deposited silts, sands and gravel islands and river bars, a common occurrence along the Columbia. It is dioecious, meaning that the trees bear either male or female reproductive parts, called catkins. So the familiar "cotton" comes only from female trees. And by the way, cottonwood pollen is an allergen, but don't blame the fluff for your sneezes. Male cottonwood trees release their pollen several weeks before the fluff flies.
The trees begin to “flower” (produce catkins) at about age 10. This usually occurs in late March or early April in our area. When the seeds mature in May and June they are released, resulting in the fine cotton fluff that we see floating on the breeze and accumulating in drifts this time of year. The seeds are miniscule, but germinate very easily if they land on suitably moist soil.
But that's not the only way they reproduce. They can also propagate vegetatively. After logging, shoots will often sprout from broken root and branch fragments. The tree also has the unusual ability to drop small shoots, complete with green leaves, onto the ground where they are able to root - or be washed to another suitable location and root there.
A common planting practice is to harvest cuttings from living trees during the dormant season, November to March. Under ideal conditions (adequate soil moisture), cuttings will grow as much as 5 feet in the first year after planting. Cottonwood is a remarkable tree due to its rapid growth and formidable stature.
Though not a tree to plant in your yard, it is the perfect riparian inhabitant. The heavy wood is soft and rots easily and is readily susceptible to storm damage. One seldom finds a mature tree that is not rife with cavities, broken branches and failed tops. These areas of damage are often perfect homes for a variety of wildlife, who use the cavities and the broken branches and tops for nesting. Eagles, great blue herons and even Canada geese will build nests in the tops of these trees. Cavity nesting birds also find numerous opportunities.
Indigenous peoples found the tree to have a variety of uses. The inner bark was peeled and eaten in late spring. The sticky buds, which are sweet, were boiled and mixed with deer fat to make a salve. Buds were also used to make a resinous glue, as a waterproofing compound, and mixed with other plant pigments to make paint. Many tribes used the leaves, buds and bark to make tinctures and curatives for a variety of disorders. The wood was used for smoking fish and making small canoes, and was burned indoors, as it produces little smoke (though it does produce a lot of ash). The flexible shoots were used in building sweat lodges and the roots twisted into rope and used for fish traps.
Today the wood, which is relatively light when dried and structurally weak, is harvested and used for a number of utility purposes. It is more commonly used for pulp and making premium grade paper, or as biomass for energy production.
Cottonwood is a remarkable plant that stabilizes and graces our rivers and creeks, from young, fast-growing whips to massive broken-down witnesses to time.