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.   

Amphibians

 

Green Treefrog (Hyla cinerea).
Mecklenburg County, North Carolina. 

Amphibians, our frogs, toads and salamanders usually have moist skin and are dependent on water for at least part of their life cycle.  All amphibians start out as a fertilized egg.  The egg develops into a tadpole, an aquatic creature with gills much like a fish.  The tadpole then transforms into a four-legged, air-breathing land animal with lungs.  The name amphibian reflects this type of life.  It is from the ancient Greek meaning two forms of life, life in the water and life on the land. 

 

Video of frog tadpoles.

Rowan County, North Carolina. 

Amphibians are, in part, the inspiration of an impressive and enigmatic phrase I first heard while taking freshman biology, “Ontogeny recapitulates phylogeny”.  I was assigned to write an essay on this theory and that assignment sent me to the library.  Some might remember libraries; they were the internet of their day.  Scouring indices of several books yielded a definition; Ontogeny (development) recapitulates (gives a summary of) phylogeny (evolutionary history).  In the case of amphibians, the theory says they pass through the single-cell organism stage, then become a fish-like animal, then a land animal.  This sequence supposedly recapitulates vertebrate evolution because all vertebrates have a similar developmental sequence.  Further reading informed me ontogeny recapitulates phylogeny is no longer accepted by science.  The similarity of development among vertebrates is a reflection of their common ancestry not some form of genetic memory. 

North Carolina is the home to 71 species of amphibians.  Much of this diversity is from the dizzying array of salamanders found in the North Carolina mountains.  

The Red Eft stage of the Eastern Newt (Notophthalmus viridescens).
Ashe County, North Carolina. 

The Red Eft is the juvenile stage of the Eastern Newt (Notophthalmus viridescens), a species of salamander.  The Eastern Newt is found throughout North Carolina.  Tadpoles of this salamander metamorphose into the Red Eft. This is a highly terrestrial stage of the Eastern Newt life cycle.  Red Efts may walk long distances to reach distant bodies of water.  This wide-spread dispersal prevents inbreeding in the species.  After spending several years as a Red Eft, the Eastern Newt undergoes a second metamorphosis into the aquatic adult, the reproductive stage.  Red Efts have rough, dry skin, an unusual feature in salamanders.  This is an adaptation to the dry environment most salamanders avoid.  The Red Eft’s color is a warning.  The brilliant red lets predators know the Red Eft’s skin is permeated with tetradotoxin, a powerful neurotoxin and so should not be eaten.

Marbled Salamanders (Ambystoma opacum).
Rowan County, North Carolina. 

The Marbled Salamander (Ambystoma opacum) is another widespread amphibian species.  This rather large salamander is black with white bands on its back.  They hide under leaves and logs, and they eat worms, slugs and insects.  During the fall, Marbled Salamanders mate and the females lay eggs in forest depressions. As the depressions fill with rainwater, tadpoles develop and metamorphose into the adult stage. 

Cricket Frog (Acris crepitans).
Mecklenburg County, North Carolina. 

Frogs and toads are another major group of amphibians and are well represented in North Carolina. Northern Cricket Frogs (Acris crepitans) are usually found on the Piedmont of North Carolina.  This tiny frog is brown and green, has warty skin, a dark triangle on the head and a Y-shaped pattern on the back.  The call of Northern Cricket Frogs is a series of rapid clicks resembling the sound of its insect namesake. 

A Green Treefrog blending into foliage.
Rowan County, North Carolina. 

Several treefrogs are found in North Carolina.  Treefrogs are rarely found on the ground and have large toepads that allow them to climb vertical surfaces.   Among the most common are the Green Treefrog (Hyla cinerea) and two species of Gray Treefrogs (Hyla chrysoscelis and Hyla versicolor).  Green Tree Frogs live on the Coastal Plain and Piedmont of North Carolina where they blend in perfectly with vegetation.  Their green color is set off by a white stripe on each side and golden spots on the back.  

Cope's Gray Treefrog (Hyla chrysoscelis).
This frog used the adhesive pads on its toes
to climb up a glass window pane. 
Rowan County, North Carolina. 

Cope's Gray Treefrog seen from below.
Rowan County, North Carolina. 

A Cope's Gray Treefrog looking out from a Bluebird box.
Rowan County, North Carolina. 

The two species of Gray Treefrogs found in North Carolina belong to a cryptic species complex and are visually indistinguishable.  H. chrysoscelis is called Cope’s Gray Treefrog and H. versicolor is the Gray Treefrog.  Both Gray Treefrogs are mottled gray, brown and green and can change their color, chameleon style.  The underside of these frogs is white with bright yellow on the hind legs.  The two species can be distinguished by their calls, with H. chrysocelis having a faster call than H. versicolor.  A definitive if not very practical way to distinguish the two Gray Treefrogs is by counting their chromosomes.  H. chrysoscelis is diploid, with two copies of each chromosome, while H. versicolor is tetraploid with four copies of each chromosome.   The speciation event that produced the two species of Gray Treefrogs occurred by of multiple hybridizations between H. chrysoscelis and several related treefrog species that are now extinct.  

Fowler's Toad (Anaxyrus fowleri).
Dare County, North Carolina. 

Toads are related to frogs but with dryer, warty skin.  The legs of toads are shorter than those of frogs and this makes them more likely to crawl than hop.  Fowler’s Toad (Anaxyrus fowleri) is found throughout North Carolina, from the mountains to the coast. This medium-sized toad has a gray body with dark brown spots. 

 Amphibians are intrinsically interesting creatures but they are also sensitive indicators of environmental quality.  The moist skin of amphibians absorbs not only water and oxygen, but also toxins and pollutants. This makes amphibians sensitive to environment degradation and many species are in decline.  Perhaps worse than pollution is amphibian susceptibility to novel infectious diseases. Two species of infectious fungi called chitrids have emerged in the last 30 years and have devastated many species of amphibians around the world.  Frogs, toads and salamanders are treasures.  Their forms, colors and calls are a delight, and they tell us a story we need to hear.