Sweet birch, Bengay and beer

Found in the mountainous regions of the Mid-Atlantic states and broadly across the Northeast and New England, sweet birch (Betula lenta) grows to about 60 feet in height, with a single straight trunk and a round, spreading crown.

In its youth, sweet birch sports dark, smooth skin that strongly resembles cherry bark, giving rise to its other common names, black birch and cherry birch. Bark of mature trees is cracked.

Like other birch species, sweet birch leaves are alternate, serrated and with distinct ribs. But the dead giveaway that you've got a sweet birch is to take a whiff of a broken fresh twig: it will smell conspicuously like wintergreen, or to some noses, root beer.

Oil of wintergreen, known chemically as methyl salicylate, is the substance responsible for this distinct aroma. It is closely related to the active compound in aspirin and has a huge range of applications in industry. It is now manufactured synthetically in the lab but once was distilled exclusively from the sap of the sweet birch. Rubbed on the skin, methyl salicylate causes a warm, tingling sensation, which makes it a common ingredient in muscle and joint pain creams like Bengay. In high concentrations, it is extremely toxic, causing stomach problems and kidney failure when ingested.

Used sparingly, the oil imparts a minty essence to foods and candies, including Life Savers, root beer and various medicines. As a historic medicine, oil from sweet birch was invaluable to colonists and Native Americans as an antiseptic and in first aid for burns, warts, dandruff and fever, as well as chronic illnesses including cancer, dysentery and rheumatism. Fortified with honey and allowed to ferment, watered-down sap became birch "beer," an agreeable refreshment in Colonial times.

Lumber from the durable wood of the sweet birch has been used in cabinets, veneers and as an addition to paper pulp. Because it darkens as it ages, it comes to look like mahogany, though birch wood is much harder. However, sweet birch can take up to 150 years to attain a size useful for larger projects, and for that reason it is mainly used in flooring and for smaller projects.

In the landscape setting, sweet birch prefers cool locations with moist, well-drained soils. It requires little fertilization, and will stand out in the fall with its deep yellow color. A wide range of songbirds and mountain-dwelling ground birds seek out sweet birch catkins and fruit, and animals including deer, rabbits and porcupine browse the tree's bark and twigs. It is resistant to many of the insect pests that affect other birch species, and is an important butterfly host plant. In the wild, sweet birch is often found growing alongside white pine, red oak, American beech and white ash.

Michelle Donahue, a Frederick County Forestry Board member, contributed this column.

Nature Notes for 3/11/2012