When the Earth cooled during the Pleistocene, the continental glaciers that formed in the northern latitudes flowed southward slowly enough that tree species across North America were able to survive the advancing ice sheets by migrating southward. This was possible because each new generation of tree seedlings, growing from those seeds that happened to have been dispersed south of their parents, were able to grow to maturity (and then produce new seeds, some of which dispersed still farther south) faster than the cooling climate destroyed their habitat. This migration took tens of thousands of years to complete, and the snowbirds’ return journey, which began once the ice sheets stopped advancing and began to melt and break up, took an equally long time.
In Europe, on the other hand, this migration couldn’t take place. When European trees – including many hickory species – tried to migrate south, they were pressed up against the impassable east-west mountain ranges: the Alps, Pyrenees, or Carpathians. This is why there are no longer any hickories in Europe and why European colonists were unfamiliar with this interesting group of trees when they first arrived in North America. Outside of the 13 hickory species in North America, there is one other species, in Asia.
New England colonists must have picked up on the importance of shagbark hickory right away, for Native Americans used all parts of the tree and held it in high esteem. If a mother’s milk was not available, babies were fed shagbark hickory nut milk mixed with dried bear or deer meat. Hickory milk, made by boiling the crushed nuts of shagbark hickory, was an important item in the adult diet as well. Oil pressed from the nuts was used for cooking, hunting bows were made from the wood, and stone axe heads were bound to their handles by flexible, young hickory twigs.
European immigrants soon found many other uses for hickory, especially shagbark. They learned that the toughness of the wood – though not the very strongest wood, nor the most elastic, it combines these traits to be the toughest – makes it the best choice for punishing uses such as tool handles, wagon wheels, barrel hoops, dowels, and ladder rungs.
In 1827, Marcus Bull published Experiments to Determine the Comparative Value of the Principal Varieties of Fuel, the results of his tests of the fuel value of 46 tree species. This established the truly superior heating value of shagbark: it weighs in at 4,469 pounds of dry wood per cord. A shagbark cord also produced the most charcoal: 1,172 pounds, capping its reputation for utility. (It has since been found that black locust, not widely distributed in those days, edges out shagbark in the firewood contest.)
Wooden wagon wheels and barrel hoops are not so common now, but shagbark hickory wood is still used for smoking meats and cheese, where its long-lasting coals and subtle flavor are very much appreciated.
The range of shagbark does not extend to northern New England, so I only see it when I take a dip to the south. But it is such a remarkable tree that vivid memories come back home with me. The smoke-gray color and the rampant shagginess of a shagbark’s bark make the species easy to pick out, even from a distance. Long, large strips of the bark peel away from the trunk from both top and bottom before dropping to the ground to make room for another peeling layer. Open-grown shagbarks are beautiful oddballs that add interest to any landscape, the very stout twigs and branches presenting a striking winter outline. They grow slowly and have a long taproot that makes them difficult to transplant, two traits that do not endear them to the nursery trade.
The large compound leaves are 8 to 14 inches long, and usually have five obovate (oval, broadest toward the tip) leaflets. Shagbark hickory’s flowers open just before the leaves have reached full size, with male and female flowers on the same tree. The nuts ripen in October in New England and New York, and in September farther south. Its range covers most of the eastern United States. In the north, it is more common in upland habitats; in the heart of its range, bottomlands are preferred.
The sweet and bountiful nuts are less appreciated by people nowadays, but many wildlife species make significant use of them. They are eaten by wood ducks, mallards, wild turkeys, chipmunks, white-footed mice, both red and gray foxes, gray squirrels, red squirrels, and flying squirrels. Squirrels also disperse the seeds. The brown creeper often tucks its nests under the curls of the bark.
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