Nature’s notebook

Nature’s exfoliation – for trees

River birch trees at Morton Arboretum.

A while back a friend sent me a picture of the beautiful river birch on her property near Troy. Another friend is proud of the sycamore tree in her front yard, which sold her on the house where she lives. This got me thinking about the trees in our eastern U.S. forests that possess exfoliating bark. The term exfoliating or peeling bark describes the natural process and condition of the bark peeling away from a tree trunk.

River birch (Betula nigra) is a deciduous tree native to the eastern United States, north to Minnesota, west to Kansas and south to Florida. They are restricted to stream banks and other moist places and can grow up to 70 feet tall and 30 inches in diameter. They are one of the few heat-tolerant birches in a family of mostly cold-weather trees.

The bark of the river birch is distinctive – gray-brown to pinkish brown to ivory, exfoliating in curly papery sheets. Leaves are alternate, simple, and oval shaped with serrated edges. Fruits mature in late spring, making it a valuable tree for wildlife. White-tailed deer browse the twigs, buds and foliage, and grouse, turkeys, small birds and rodents eat the seeds.

The American sycamore (Platanus occidentalis) is another lowland species native to North America. They too have exfoliating bark that flakes off. This leaves the surface of the tree mottled and greenish-white, gray and brown. The bark has to give way to a growing trunk by stretching, splitting or infilling. Sycamore bark is rigid, and will not stretch to accommodate the growing tree underneath, so the tree sheds it.

The distinctive bark of a sycamore tree. Photo: By Dwspig2 (talk) - self-made, CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=15940932

The sycamore grows to a larger trunk diameter than any other native hardwood. The present champion tree’s diameter is 11 feet, and there are records of some that were up to 16 feet in diameter. Sycamore trees can grow from 100 to 150 feet tall. They also have the largest leaves of any native tree in North America. They are one of the oldest species of trees on earth. Small animals like squirrels commonly den in sycamores because of the warped, twisted branches.

The shagbark hickory (Carya ovata) is a large, deciduous tree growing in the eastern United States and Canada. They can be more than 100 feet tall and live more than 350 years. They have shaggy bark, as their name implies, though it looks different from the bark of the river birch or sycamore. It is thicker and more prominent, as long peeling strips. The nuts of a shagbark hickory are edible and were an important food source for Native Americans and early settlers. They are eaten by a wide variety of wildlife. Some species of bat may roost behind the shaggy bark of a shagbark hickory. The trees grow best on moist but well drained soils in humid climates. A fun fact: Andrew Jackson, the seventh U.S. president, was nicknamed “Old Hickory” because he was considered to be as tough as a hickory tree.

These trees with exfoliating bark have a unique look. River birches look delicate and pretty, while shagbark hickories look coarse and shaggy. Keep your eye out for these species on your next walk in the woods and take a minute to notice their distinctive look.