Cottonwoods Along the Bitterroot

Cottonwoods changing colors along the Bitterroot River

Cottonwoods along the Bitterroot River (photo Rick and Susie Graetz)

Cottonwoods hug the river bottoms with bright yellow leaves making a vivid contrast with the clear blue skies of fall. These trees earn their name from early June to mid-July as the female trees release clouds of cottony white fibers carrying tiny brown seeds away in the wind. As their seeds are dispersed, many end up landing on the surface of water and are then stranded along eddies and river banks. If the river level does not fluctuate too much, allowing the seed to establish itself, seedlings will start to take hold.  As the water level drops with late summer droughts, one can often walk along a sandbar and see a row of these newly sprouted cottonwoods at the former waterline. 

There are many different species of cottonwoods but one thing they all have in common is their love for high soil moisture. Although they can survive in low moisture conditions, cottonwoods do not begin to achieve their height and growth potential in arid soils. In fact, they can survive with short-term partial inundation—conditions that would kill most all our native trees. Some cottonwood stands in Montana are suffering from decreased regeneration due to man-made interruptions in natural flows of the riparian community.

Cottonwoods are incredibly valuable for wildlife. Given that they are riparian residents, it seems like every gnawing and browsing animal thrives on cottonwood bark, leaves and cambium. Beavers do not shy away from the thick, furrowed bark for eating and lodge building. In the winter months, ruffed grouse depend heavily on cottonwoods for forage and roosting sites. Large cottonwoods make excellent nest platforms for birds of prey like osprey and bald eagles. As the tree ages, it lends its decaying trunk to song birds and cavity nesters.