Betula alleghaniensis Britton

Betula alleghaniensis is one of the most handsome birches, cultivated for its distinctive bark and rich yellow autumn colour, as well as for the brilliant translucency of its young leaves. The species can often be recognised solely by its trunk, which typically has metallic glinting bark with thick persistent flakes that curl back on stouter stems and branches, developing into thick plates on older trunks, which can become almost black. These bark characteristics are unique in the genus, no other birch having bark with this burnished, peeling character. The trunks are buttressed and have silvery ‘toes’ streaked with lenticels at the base of the trunk, which form as the roots spread out near the soil surface.

Beetula alleghaniensis is closely related Betula lenta, but that species differs in its thinner, smooth, polished and almost hairless twigs, smaller and more sharply pointed buds. Typical B. alleghaniensis has thicker matt hairy leaves with fewer, more impressed veins, double-toothed in characteristic ‘stepped’ fashion with a deep notch above each major tooth interrupting the run of secondary teeth between. The major teeth are 4–5 mm wide at their base, while B. lenta has teeth to 2 mm wide at the base, though this may not always be evident, especially in shade leaves; B. alleghaniensis also has more downy shoots and larger fruiting catkins with larger and hairy scales. B. lenta also differs in its close, dark-brown bark (though the bark of some forms of B. alleghaniensis approaches that of B. lenta, risking confusion – see below). Another close relation, Betula grossa, is not nearly so downy on twig and leaf, has bigger outward-pointing buds, a much narrower vein-gap with more impressed veins, and dark, scarcely glinting bark like that of B. lenta. Perhaps the most useful qualitative character is that in B. alleghaniensis the leaf underside and petiole have both silky and short puberulent hairs, while puberulent hairs are totally absent on the leaves of B. grossa.

Yellow Birch occurs throughout eastern North America from the southern parts of Quebec and Labrador in the north, reaching to 49°N in Quebec and as far west as Minnesota and western Iowa, south in the Appalachians to northern Georgia and Alabama; it is very common in New England. Throughout its range it occurs in mixed forest, in association with Acer saccharum (Sugar Maple), and Fagus grandifolia, both in lowland high forest and, further south, at high altitudes (especially with the beech). It is the most important of all birch species for timber, although as a product its wood is usually not distinguished from that of B. lenta or indeed the Japanese B. maximowicziana. The wood is hard, heavy and moderately strong and can be of large dimensions – trees can reach 30 m in height.

While the species forms shapely timber trees in forest environments, at higher altitudes, the trees of Betula alleghaniensis can look very different, as on Bromley Mountain in Vermont where they are scrubby and dwarfed, and in the Appalachians further south, where – as, for example, on Mt Mitchell in North Carolina – they are taller but gnarled, twisted and windswept, mostly showing the flaky and plated bark of older trees. Here the species shares dominance to the tree-line (the ‘balds’) with beech, almost as if it had here assumed the ecological role of the mountain birch B. cordifolia. In this southerly, and possibly drier environment, the more deeply rooting B. alleghaniensis occupies the ecological position filled further north by white-barked birches.

The species was first named by François André Michaux (1770–1825) in his Histoire des Arbres Forestière published in 1811. He called it Betula lutea, but this name proved to be illegitimate, and the correct name is the one published by Nathaniel Britton in 1904 – ironically, for a species he considered distinct from both B. lutea and B. lenta. The vernacular name Yellow Birch is, in a sense, a wishful euphemism, in that very often stems are brownish, though they do glint vividly in the sun once the canopy has been thinned by sharp frosts. McAllister and Ashburner (2013) report the name ‘merisier’ for the species in Quebec. However, this name – which originally applied to the European Bird Cherry, Prunus avium – properly belongs to Betula lenta, the Cherry Birch, with which B. alleghaniensis in southern Quebec (and also Ontario) has often been confused, since in those districts trees often have non-exfoliating dark-brown bark (described as the forma fallax), not the flaky bark of the type (Brayshaw 1966).

Trees thrive where there is plenty of moisture, but appear to grow perfectly well in drier conditions, although in the British Isles they never seem to be fast-growing – not necessarily a disadvantage in the smaller garden. Collections from the Canadian Maritimes (Nova Scotia, New Brunswick and Prince Edward Island) and New England seem to grow best and most rapidly in the British Isles, as do those with inland provenances, for example from the north shore of Lake Huron. Less suitable, and perhaps too slow-growing, are the southerly montane ones from North Carolina and Virginia. In garden or arboretum, it is the yellower bark of younger trees which is most attractive. Clones selected for the best bark colour could be grafted onto seedling Betula alleghaniensis itself, or even onto B. lenta, in preference to B. pendula or B. papyrifera stocks. Seed has a high viability, and when harvested in gardens or arboreta seems to come entirely true. Cuttings of young shoots would be expected to root easily under mist.