Tree Bark Identification: Reading the Trunk

Bark identification works best as a sorting exercise rather than a matching exercise. University of New Hampshire Extension, following Michael Wojtech's classification, sorts bark into seven categories:

• Peeling horizontally — yellow birch
• Lenticels visible — black birch, big tooth aspen
• Smooth unbroken — beech, red maple
• Vertical cracks or seams — scarlet oak, shagbark hickory
• Vertical strips — pignut hickory, mature shagbark hickory
• Scales or plates — black cherry
• Ridges and furrows — pitch pine, northern red oak

Stand back far enough to see the whole trunk, decide which of the seven it is, and only then start comparing species. This is the identification route that still works in winter, when there are no leaves to check against the leaf key.

The single most common bark mistake is reading the wrong part of the tree. University of New Hampshire Extension points out that as a tree matures it passes through young, mature and old bark stages, and that some older trees show all three at once — old bark at the base of the trunk, younger bark on the branches at the top.

Practical rules that follow:

• Look at the trunk at roughly chest height on a full-grown tree
• Compare several trees of the same kind rather than deciding from one
• Prefer trees in a natural setting over ornamental plantings, which skew toward cultivars
• Ignore moss, lichen and climbing vines; they tell you about the site, not the species

If the tree is young and smooth-barked, take a leaf, a twig and a bud photograph too. Bark on a sapling frequently looks nothing like the same species at sixty years old.

Understanding the mechanism makes the categories stick. The Arnold Arboretum's account: everything outside the vascular cambium eventually becomes bark. The innermost part is phloem, which conducts sugars and other carbon-based nutrients through the tree. Outside that, a cork cambium produces cells whose interiors die and become gas-filled pockets — phellem, commonly called cork.

As the trunk expands, the outer cork layer stretches and cracks, and a new cork cambium forms deeper inside, sometimes in the older outer phloem. In some species each new cork cambium forms a complete sleeve; in others it forms many small overlapping patches. That difference is exactly why one species ends up with long vertical strips and another with small plates.

Lenticels are the exception in the cork layer: patches of loosely packed cells with air spaces that let internal tissues exchange gas. On paper birch they form a prominent and characteristic part of the bark's appearance; on other species they hide at the bottom of cracks.

Bark alone rarely closes a case, because several species share a pattern. Pair it with whatever else the tree is offering:

• Branching. Opposite branches point to maple, ash, dogwood, Caprifoliaceae shrubs or horsechestnut; alternate branching covers everything else
• Buds and leaf scars. Ash carries a squat terminal bud above a leaf scar that dips down like a smile
• Fruit on the ground. Acorns, samaras, nuts and cones survive winter under the tree
• Shape and site. American elm keeps its vase-shaped crown with drooping limbs even when bare

Photograph the trunk straight on from a few feet back so the whole pattern is in frame, then a close shot to show texture, then the branching. Photograph it with the app and it identifies the tree; the extra shots are what let you check the answer against what you are actually looking at.