Cottonwoods

Cottonwood Encounters

Historian and biologist Paul Russell Cutright believed that the Lewis and Clark Expedition could have managed without the cottonwood tree, but he couldn’t imagine how.^[1]Paul R. Cutright, Lewis and Clark: Pioneering Naturalists (Lincoln and London: University of Nebraska Press, 1989 First Bison Books printing), 332. The tree certainly provided much. Cottonwood was used to build Fort Mandan, carve twelve of their seventeen dugout canoes, and to make hand trucks to haul their heavy boats and equipage around the Falls of the Missouri (See The Portage Route). The trees provided shade and firewood in otherwise barren country and the twigs and bark fed their horses during the cold Northern plains winter of 1804–05.

Given cottonwood’s propensity to cross-pollinate among its many species, identifying the ones they encountered may never be exact. Broadly, they saw Eastern cottonwood moving down the Ohio and up the Mississippi. On the Missouri River, they encountered plains cottonwood—many of them in large rafts of driftwood or sawyers and snags waiting to puncture unsuspecting boats. On the Teton River near Decision Point, mentions were made of a new variety with narrow leaves. Most botanists think they saw narrowleaf cottonwood. When they crossed the Continental Divide and entered the Columbia River basin, the cottonwoods eventually transitioned to black cottonwood. Finally, on his return from his second Marias River exploration, Meriwether Lewis found “the three species of cottonwood” which he had remarked in his voyage “assembled together”. Some botanists believe he was witnessing a fifth Populus species, balsam poplar (Populus balsamifera).^[2]Lewis, 26 July 1806, Moulton, 8:128; Charles S. Sargent, “The First Account of Some Western Trees,” Part 2, Garden and Forest: A Journal of Horticulture, Landscape Art and Forestry, 10, … Continue reading

In the “Plains Cottonwood” figure an old cottonwood rests beside a youngster—likely its offspring—near the Missouri River at Lower Portage Camp. It was here that Sgt. Patrick Gass had wheels and supports made from a solitary cottonwood growing here.

Identifying Cottonwoods

Sometimes cottonwood species are hard to distinguish from one another. They can generally be identified by their location and elevation, and also the characteristics of the leaves such as width, edge type, color, sheen, and leafstalk length. For example, the narrowleaf’s leafstalk, also called the petiole, is less than one-third the length of the midrib. Its color is the same shade of green on both sides. In the above figures, notice the relatively smooth edge of the black compared to the notched edge of the Eastern. However, the cottonwood tree’s grip on life is so tenuous that Nature allows it to hybridize in order to prevail. Where ranges overlap, cross-pollination influences the new tree’s characteristics—especially the leaves. The broad leaves of black cottonwood can become quite narrow when its seeds have been pollinated with narrowleaf cottonwood. This, incidentally, illustrates one reason botanists don’t rely on leaves to determine the identities of plants, but rather on fruits.

Fruits and Seeds

In the spring, male trees ship pollen—fiber so fine that it’s seemingly perceivable only by the sinuses of allergic humans—on the wind to any and all available female trees to fertilize their flowers. The next stage is the emergence of the fruit. Each female cottonwood tree produces thousands of fruits, and inside the husk of each are hundreds of seeds. Each female cottonwood tree, depending on its size, may produce millions of seeds.

The fruit ripens until the pods, now dry, burst like popcorn, presenting their seeds for the wind to distribute. The white, cottony filaments are the sails by which the seeds will be dispersed. On windy days, the result can be blizzard of cotton. It can be such a nuisance that many cities prohibit the planting of female cottonwoods. Nature has scheduled this part of the process to take place over several days for each tree, timed to coincide with the peak of spring runoff, or just after the peak, so that silty places along the banks will still be wet enough to satisfy the seeds’ immediate need for water.

The seeds are so small that they contain no food reserves, so those that germinate are the comparatively few that luck onto the ideal homesite. In the short term, that means a successful seed must alight on soil that is soft and moist, typically close to the edge of a stream. Furthermore, there must be no other vegetation nearby to compete for available water. If those conditions are met, the seed immediately begins to send down a root, which follows the water table as it recedes during the future tree’s first summer. In the long run, it must be far enough away from the stream that a winter’s ice will not scrape it away while it is still young.

At best, life is hard for a young cottonwood tree. To grow and thrive it needs as much sun as it can get, so if other trees, even other cottonwoods, are too close, it must spend extra energy to stay in the light. Besides, cottonwood trees contain a lot of sugar, and it’s a fortunate seedling or sapling that escapes a wild ungulate’s appetite.

Ethnology

The inner bark of cottonwoods were^[4]When referring to the ethnobotanical record, past tense will most often be used. This does not imply the plant is no longer in use in the manner described. sources of food for Native Peoples across North America. Even their horses fattened on its twigs, branches, and inner bark. Several tribes used the resinous buds as chewing gum, and many made dyes, paints, and even glue from them. The aromatic balsam found in the buds could be used to mask human scent when hunting or stealing horses. With many Plains Indians, cottonwood logs were seen as the ceremonial center pole in Sun Dance lodges. Some Montana Indians even added the inner bark to their kinnikinnick smoking mixtures. The Nez Perce made a poultice from black cottonwood leaves for sore muscles and also their horses’ sores.^[5]Daniel E. Moerman, Native American Ethnobotany (Portland, Oregon: Timber Press, 1988), 427–431.

Although several cottonwood species were traditionally fed to horses, the captains learned of the practice from the Mandan and Hidatsas:

. . . the horses appeared much fatieged I directed some meal brands given them moisened with a little water but to my astonishment found that they would not eat it but prefered the bark of the cotton wood which forms the principall article of food usually given them by their Indian masters in the winter season; for this purpose they cause the trees to be felled by their women and the horses feed on the boughs and bark of their tender branches.^[6]Meriwether Lewis, 12 February 1805, The Definitive Journals of Lewis & Clark, Gary Moulton, ed. (Lincoln: University of Nebraska Press, 2002), 3:292.

Ethnologist Gilbert Wilson who for many years documented Hidatsa lifeways, adds these details:

Twigs and smaller branches they ate readily; but limbs as thick as my wrist, they stripped of bark with their teeth. For this reason, the twigs and branchlets had been cut off and were piled by themselves. The thicker limbs, thus freed of branches, were more easily stripped by the ponies’ teeth.^[7]Gilbert L. Wilson, The Horse and the Dog in Hidatsa Culture, Anthropological Papers of the American Museum of Natural History, Vol. XV, Part II (New York: American Museum Press, 1924), 175–76, … Continue reading

Plains Cottonwood

In the literature, plains cottonwood may appear as one of its many synonyms including: P. sargentii Dode; Populus monilifera Aiton; and Populus deltoides Bartr. ex Marsh. var. occidentalis Rydb. Botanists still debate which Latin binomial best applies to the tree.

Plains cottonwood grows along the length of the Missouri River and also west of the Continental Divide. Moving north through the Bitterroot Valley in early September 1805, they would have seen the ancestors of some of the largest plains cottonwoods in the contiguous United States.^[8]The 2012 US national champion was in Ravalli County, Montana standing 112 feet high with a crown-spread of 94 feet. American Forests (2012). Archived from the original at web.archive.org. Lewis preserved a specimen on the return trip, and it is part of the Lewis and Clark Herbarium at the Academy of Natural Sciences of Philadelphia. Apparently, Lewis’s original label was rewritten—and likely shortened—by Frederick Pursh: “Cotton tree of the Misisippi & Missouri. Augst. 1806.”^[9]Moulton, 12:46; James L. Reveal, Gary E. Moulton, and Alfred E. Schuyler, “The Lewis and Clark Collections of Vascular Plants: Names, Types, and Comments,” Proceedings of the Academy of … Continue reading If it was collected in August 1806, he could have done so anywhere between the Musselshell River and Yankton, South Dakota.

“Plains Cottonwoods” figure: A cluster of young plains cottonwood trees grows on a shoreline altered by the 1947–1953 construction of Garrison Dam—one of six mainstem Missouri River dams and the fifth-largest earthen dam in the world.

Narrowleaf Cottonwood

Narrowleaf cottonwoods are sometimes called mountain cottonwood because they like to grow between 3000 and 8000 feet in elevation.^[10]Elbert L. Little, National Audubon Society® Field Guide to American Trees (New York: Alfred A. Knopf, 1980), 340–41. Due to its scarcity and poor-quality lumber, narrowleaf cottonwood is not a commercially desirable plant. In 1805, it was, however, a top candidate for Lewis’s plant collection. Likely, it was one of the specimens lost to a flooded cache at White Bear Islands above the Falls of the Missouri. It was the only cottonwood species for which he wrote a botanical description, and he is credited with being the first to do so.

He may have collected his specimen on the Teton River or around the Falls of the Missouri while waiting for the portage to be completed and the iron-framed boat assembled. During his 1806 return, his lightly-equipped Marias River exploration and subsequent flight from any pursuing Blackfeet likely prevented him from collecting a replacement. Once he re-connected with his detachments near present Fort Benton, he was determined to move the boats down the river—quickly. He was soon out of range of both the Blackfeet and the narrowleaf cottonwood. His 12 June 1805 description reads:

The narrow leafed cottonwood grows here in common with the other species of the same tree with a broad leaf or that which has constituted the major part of the timber of the Missouri from it’s junction with the Mississippi to this place. The narrow leafed cottonwood differs only from the other in the shape of it’s leaf and greater thickness of it’s bark. the leaf is a long oval acutely pointed, about 2½ or 3 Inches long and from ¾ to an inch in width; it is thick, sometimes slightly grooved or channeled; margin slightly serrate; the upper disk of a common green while the under disk is of a whiteish green; the leaf is smoth. the beaver appear to be extremely fond of this tree and even seem to scelect it from among the other species of Cottonwood, probably from it’s affording a deeper and softer bark than the other species.—^[11]Moulton, 4:280–81.

Narrowleaf cottonwood would not be fully described until it was encountered in 1823 by Long’s Expedition in the southern Rocky Mountains of Colorado.^[12]Sargent, Part 1, 10, no. 1 [January 20, 1897]: 28.

Black Cottonwood

Ranging between 60 and 120 feet in height, black cottonwoods are the tallest native Populus species. Of all the species discussed here, they are the only one classified as a hardwood—the tallest hardwood in North America. They grow at lower elevations in almost any type of soil, although east of the Cascade Range, they seek streams and ponds in protected valleys and canyons.^[13]“Populus balsamifera L. ssp. trichocarpa (Torr. & A. Gray ex Hook.) Brayshaw”, USDA Natural Resources Conservation Service PLANTS Database, plants.usda.gov/plant-profile/POBAT.

Lewis preserved a black cottonwood specimen on the “Columbia River. June: 1806”.^[14]Moulton, 12:46, Reveal et. al., 40. The date indicates that he meant the Columbia River Basin, not the actual river. He likely collected the specimen on the Clearwater River while at Long Camp in present Kamiah, Idaho. Lolo Creek near Travelers’ Rest is another possibility. Both streams are tributary to the Columbia.

Summary

Cottonwood trees demonstrate remarkable resiliency and provide immense benefits to their environments. Adaptable to a range of soils and conditions—from the Ohio, Mississippi, Missouri, Yellowstone, and Columbia Rivers—these trees thrive in diverse landscapes. Their fast growth and substantial size, especially evident in black cottonwoods, offer vital resources such as timber for construction and boat building. The bark and leaves support local wildlife, including beavers that preferentially select certain species for food and shelter. Without cottonwoods, the Lewis and Clark Expedition would have faced far greater challenges, highlighting the tree’s indispensable role in both the natural world and human history.