Cottonwood Spring

 

Leaves of Eastern Cottonwood (Populus deltoides).
Rowan County, North Carolina. 

The Wil-Cox Bridge spans the Yadkin River at the historic Trading Ford near our home in Rowan County, North Carolina.  The bridge opened to automobile traffic in 1924 and today is a pedestrian trail across the river.  This bridge, thirty feet above the floodplain, gives a closeup view into the canopy of the forest that lines the Yadkin River.  This spring we made several trips to the bridge and watched the trees deploy their leaves and flowers.  The Eastern Cottonwood (Populus deltiodes) was one of these. 

The Wil-Cox Bridge over the Yadkin River. View from
Davidson County looking toward Rowan County. 

Eastern Cottonwoods thrive along rivers. They get their name from the cottony seeds that are dispersed in their millions by the wind.  The triangular leaves give the tree its specific name, deltoides.

A triangular leaf of Eastern Cottonwood. 
Rowan County, North Carolina. 

Despite its name, Eastern Cottonwoods can be found across much of the United States.  It was originally classified as three different species.  These three trees were lumped into a single species with  distinct subspecies. The eastern-most of these is now Populus deltoides deltoides.  This is the Cottonwood we have in North Carolina.  On the Great Plains, the Plains Cottonwood (Populus deltoides moniifera) thrives along the rivers.  The Rio Grande Cottonwood (Populus deltoides wislizeni) grows from Colorado to Texas and west into Arizona. 

Male flowers of Eastern Cottonwood.
Rowan County, North Carolina. 

Female flowers of Eastern Cottonwood.
Rowan County, North Carolina. 

Eastern Cottonwoods flower before the trees leafs out in the spring.  Cottonwoods are unusual because they have separate male and female trees, a condition botanists call dioecious.  Male trees produce a pendulous catkin of red flowers that lack sepals or petals but have pollen producing stamens. Female trees make catkins with multiple flowers with carpels that contain the eggs.  The female flowers are wind pollinated and after pollination, the fruits begin to develop. The flask-shaped fruits hang in strings and give us another common name for the Eastern Cottonwood, Necklace Poplar.  

Fruits of Eastern Cottonwood.
Rowan County, North Carolina. 

When the fruits are mature, each splits open and releases scores of tiny seeds covered with fine cottony hairs.  These seeds catch the breeze and fly away.  Many of these seeds land in inhospitable places but some end up in the river.  The seeds float downstream and may lodge on sandbars to produce a new trees.  Eastern Cottonwood seedlings need full sun and abundant water to thrive. Riverbanks and sandbars provide the perfect place to grow.

Eastern Cottonwood seeds being
released from mature fruits.
Rowan County, North Carolina. 

Video of flying Eastern Cottonwood seeds. 

Rowan County, North Carolina. 

Dozens of Eastern Cottonwood seeds with their cottony hairs.
Rowan County, North Carolina. 

Eastern Cottonwood grows very quickly and can reach 10 feet in height in the first growing season.  Mature trees may top out at over 100 feet and the Eastern Cottonwood is important in preventing erosion of riverbanks.   

Eastern Cottonwoods represent different things in different parts of the country.  In the east they are part of the green wall that lines watercourses.  On the plains they are the sign of water that can be seen from miles away.  In the Rio Grande Valley, Eastern Cottonwoods are the cornerstone species of the unique bosque forest.  But everywhere this thirsty, fast-growing and prolific tree is found, it is a keystone of its environment.