Tree Party Express II: Second of 3 Series

107What holds true for tigers, holds doubly true for trees: you cannot
really understand a species until you have observed it in the wild.

A walk in the woods provides an opportunity to gain insight into how our native forest trees – some familiar, and some less so – change in appearance over the spans of their lives, adapt to varied conditions, and anchor our ecosystems.

INTERMEDIATE DIFFICULTY: Birches, Poplars, and Other Sneaky Characters

By virtue of the fact that they can be confused for very few other types of trees, birches ought to be easy to identify, but the sheer variety of species that one could potentially encounter in our region and the shades of difference between them can produce confusion until you really know them.

They’re kind of like the Neville Brothers: there always seems to be one you’re just hearing about, and you can’t really put a name to any but the most well-known two or three. However, you will easily keep them sorted once you can recognize a few indicative traits of each species.

Gray birch (Betula populifolia) may be the easiest of the group to discern because it tends to be found growing in colonies as a successional species that is rapidly out-competed once climax species such as maple and beech fill in the upper canopy. The thin-barked, chalky-gray trunk, marked at branch bases with large, dark chevrons resembling moustaches confirms the identification suggested by the species’ location and (often) multi-stemmed growth habit. Contrary to all reasonable expectations, young gray birches are often whiter in color than white birch, which can have a more polychrome appearance due to irregular exfoliation, but unlike white birch rarely exfoliate.

White birch (Betula papyrifera) often occurs as a multi-stemmed tree, but can easily be distinguished from gray and river birches by its exfoliating bark, shedding in large strips over young and middle aged tissue and marked with long, but subtle horizontal striping that becomes more pronounced with age. Also known as canoe birch, this species tends to have a multicolored appearance when it is young and actively shedding bark, but matures to a more uniform white or gray hue once exfoliation ceases. Bark color is most intense in full sun or uncongested forest conditions, with more mottled, grayer bark occurring on trees in full shade. Single-stemmed specimens can attain great age and girth.

Yellow, or silver birch (Betula alleghaniensis) is generally a tree of dimensions similar to white birch, but can occasionally grow to much greater bulk under favorable conditions. It features shiny bark that ranges in color from yellowish to silver-gray, exfoliating in small curls, and is a frequent companion to eastern hemlock. In its silver-gray form that takes hold in shade, its bark loses some luster, but still can be distinguished from the similar river birch by the relative smoothness of its bark, as well as an appearance that is neater overall compared river birch’s “fuzziness”.

Among the birches, river birch (Betula nigra) exhibits perhaps the greatest transformation in the appearance of its bark, which varies in color from reddish-brown to light gray when young, exfoliates messily in middle-age, and forms thick, nearly black plates when mature. It is a common denizen of uplands and lowlands alike, occurring in greatest number along and near river banks and other places with ample soil hydrology. The largest of the native birches, river birch is primarily a southern species whose northern limit of distribution is in our region.

Black, or sweet birch (Betula lenta) is the only species we encounter that has bark that is both shiny and dark in color, usually brown to black. Young bark is smooth in texture, but not papery, and very rarely exfoliating. Sweet birch is usually marked at an early age with large lenticels, a trait that usually only manifests in other birch species later in life. Stranger yet, these markings fracture as the tree grows, and the bark matures into scaly plates at a far earlier stage of growth than river birch, which is by comparison a massive tree. In nearly all stages of development, the bark of sweet birch is much more akin to that of black cherry (hence the alternate appellation cherry birch), and is thus easily overlooked wherever cherries are prevalent.

However, unlike black cherry, the mature bark of sweet birch retains some subtle horizontal markings that can be seen upon close inspection; and, while even the slender, hairless, reddish-brown twigs are similar in appearance to cherry, they do reveal the ultimate truth when crushed, releasing a potent blast of wintergreen. Though unremarkable in appearance, sweet birch was an historically important species since it was the source of oil-of-wintergreen, which is now produced through a more efficient industrial process that no longer involves the birch. Like sugar maple, sweet birch can be tapped in early spring and its sap fermented to produce birch beer.

By Terrence Trapp, Director of Horticulture

December 29, 2011

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