Elm trees, belonging to the genus Ulmus, are valued for their majestic, shade-providing canopy. While leaves and overall shape are used for identification, the bark remains one of the most reliable features, particularly when the tree is dormant. The elm’s bark tells a story of its species, age, and health, which is relevant given the historical impact of Dutch elm disease (DED). A close examination of the trunk’s surface texture and color provides the necessary clues for accurate field identification.
The Characteristic Texture of Mature Elm Bark
The surface of a large, mature elm tree, such as the American Elm (Ulmus americana), is defined by a rugged, deeply fissured texture. These prominent vertical furrows run irregularly up the trunk, giving the bark a coarse, rough feel. The ridges between the deep grooves are typically flattened or blocky, rather than having sharp, pointed edges.
As the tree ages, these ridges frequently cross and intersect, creating a distinctive pattern that resembles interlacing ropes or diamond shapes. This crisscrossing pattern is a hallmark of the species. Unlike the smooth or horizontally peeling bark of many other common trees, the mature elm’s thick, corky structure makes it stand out in the landscape.
Coloration, Layers, and Changes with Age
The typical color of mature elm bark is a dark grayish-brown or ash-gray, sometimes showing a subtle reddish or yellowish tint within the creases. The bark of a young elm tree begins as a relatively smooth, soft gray surface. This smooth texture persists until the tree is established, generally starting to develop the characteristic deep ridges after approximately twenty years of growth.
A unique feature for definitive identification involves examining the bark’s internal structure. If a small section is cut or broken, arborists look for a distinctive pattern of alternating light and dark layers. This layered effect, sometimes likened to a bacon strip appearance, is present in the American Elm, but the closely related Slippery Elm lacks these buff-colored patches, providing a clear distinction.
Key Variations Among Common Elm Species
Not all elms present the same heavily furrowed, grayish bark; several common species exhibit distinct variations.
Winged Elm (Ulmus alata)
The Winged Elm has a highly recognizable feature: flat, corky, wing-like growths that protrude laterally from its twigs and smaller branches. While its trunk bark is generally a gray-brown with flat ridges, these corky wings make the species easily identifiable.
Slippery Elm (Ulmus rubra)
The Slippery Elm is identifiable by its dark, reddish-brown bark that is less deeply furrowed than the American Elm. Its ridges tend to be thicker and more scaly. The tree is also named for the mucilaginous texture of its inner bark.
Chinese Elm (Ulmus parvifolia)
Often called Lacebark Elm, this species presents a stark difference with its exfoliating bark. This bark peels away in irregular patches, revealing a mottled, colorful under-layer of tan, gray, green, and orange, which is far smoother than its American counterpart.
Siberian Elm (Ulmus pumila)
The Siberian Elm also contrasts with the American Elm, displaying a lighter gray bark with irregular, shallower furrows that do not develop the same deep, crossing diamond pattern.