In Thoreau’s book The Maine Woods, he lists two hundred fifteen plant species he identified in his tour of the state, giving Latin names for all. Unfortunately taxonomists have been busily at work in the intervening century and a half, and many of the names are no longer in use. Some I wish we could have back (I don’t know what plant Thoreau was talking about when he calls one plant Aster miser (“a miserable/lousy/rotten Aster”) but I’m sure it’s a good taxonomic description). Many are if nothing else nicely descriptive and it’s easy to identify them (Trillium erythrocarpum, “red-fruited trillium,” which is the beautifully fruited Trillium undulatum; Acer striatum, “striped maple,” must surely be the boldly striped Acer pennsylvanicum).
One such nice name was Betula excelsa, “tall/lofty birch.” I knew immediately from the name that it had to be the yellow birch, now known as Betula alleghaniensis. It is the tallest and grandest of the birches, with some specimens towering over one hundred and twenty feet. Most birches tend to be fast-growing, fast-dying, fast-rotting, multiple-stemmed pioneer trees. The yellow birch, while it is certainly capable of seeding into rocky and inhospitable ground and acting as a pioneer tree – this is the tree you often find sitting directly on top of massive boulders, having successfully sent large roots around the rock – is the only birch which typically becomes a climax-forest canopy tree. It is also one of the most common and defining trees of the Catskills. Growing up in New York City I saw lots of black birch (Betula lenta) and I knew the white and gray birches (B. papyrifera and populifolia) because of their striking white bark. But the yellow birch is almost absent in the woods around New York City, and it will not grow at all south of it unless there are mountains. Even in the Hudson Valley it is not common. But it thrives in the cold, rocky, thin soils of the Catskills (and also in Maine, where Thoreau saw so much of it).
Winter is the time when we notice birches, and this species, while planted not nearly as often as the white birches, is worth our attention. In old-growth forest it is, in my experience, the grandest of our Catskill hardwoods. Not only can great old specimens send up straight and massive trunks from the forest floor, but they often have fabulous and unusual branch architecture up above. The bark, which is a satiny metallic gold when young, is equally beautiful in the tree’s old age, with a distinct wavy pattern. The wood makes superior furniture and was often called “mahogany birch,” though having split up several trees for firewood, I wonder if carpenters didn’t mill the wood because they dreaded having to split it: it is terribly stringy and incredibly resistant to the axe. However, splitting the wood produces a lovely wintergreen aroma (also available if you crush a twig). It is particularly pleasant to alternate splitting yellow birch logs and black cherry logs, savoring the completely different fragrances of the wood.
The tree’s sap also makes a fine beverage, and it may be tapped like a maple, though in my experience birches run while they have leaves, not before. I am told that in East Asia people often drink birch sap; here we have yet to make this a widespread practice, though who knows, perhaps this will be the year.
Yellow birches are rarely planted as ornamentals, and their main ornamental value seems to be as forest trees rather than field or lawn trees, but in a mixed planting or forest restoration there are few better shade trees for our area. And like all our native trees they are the food source for dozens of animal species: birds eat the seeds, caterpillars eat the leaves, sapsuckers are very fond of the sap, and of course deer browse the foliage.