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Wednesday, 30 January 2013 14:49

The hardest tree in North America

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I wrote a tribute to the black locust tree some time back. It’s time to take another look. This time around we’ll incorporate the perspectives of a French arborist who visited America during the mid-nineteenth century.

Locust is a winter tree. Outdoors, it’s durable in extreme weather and indoors, it makes superb firewood. When I refer to locust, it’s to black locust (Pseudoacacia robinia), not one of the several other species in that genus such as honey locust.  

I’m fairly competent at the identification of deciduous trees during the flowering and fruiting seasons, when I can observe bark, leaves, general growth habit, and flowers or fruit. I’m less adept during the winter months, when one I have to rely on bark, buds, and general growth habit.

One tree, however, I do recognize without any difficulty whatsoever in winter is the black locust. It’s dark-brown (sometimes grayish) deeply-furrowed and cross-checked bark is a dead giveaway. A really mature black locust tree will display bark so deeply furrowed and cross-checked it resembles an alligator’s hide. And unlike, say, a tulip poplar, the trunk of a black locust doesn’t grow straight and true. Stand at the base of one and look upward. You’ll observe that the trunk ascends in a sinuous almost serpent-like fashion, as does sourwood. And unlike, say, tulip poplar, the grain of the wood is not long and easily worked. For these reasons, black locust was never, to my knowledge, utilized in the southern mountains in the exterior construction of log cabins.

The best description of the essential attributes of black locust I have encountered is provided by Donald Culross Peattie in A Natural History of Trees of Eastern and Central North America (1950): “In the first place almost the entire woody cylinder of the trunk is heartwood, always the strongest part of a tree. It is the seventh hardest in all our sylva and, as to strength in position of a beam, locust is the strongest in North America outside the tropics. It is the stiffest of our woods, exceeding hickory by 40 percent. Of all important hardwoods, black locust shrinks least in drying, losing only 10 percent volume … The wood takes such a high polish as to appear varnished. The fuel value of black locust is higher than any other American tree, exceeding even hickory and oak, being almost the equal, per cord at 20 percent moisture content, of a ton of anthracite coal.

“Yet with all these splendid qualities black locust is not even mentioned in the usual lumbering statistics. The chief reason is that the locust borer beetle (Megacyllene robiniae) is so ruinous in many regions that black locust is too seldom found in sound condition. Locust boards are therefore almost unknown, and the only common uses has been for fence posts, railway ties, and small articles such as rake teeth, ladder rungs, and (in the days when such things were in common use) buggy whips and policemen’s clubs.”            

During the era of wooden-hulled sailing ships, treenails (wooden pins) fashioned from black locust were utilized in European shipyards for pegging the planking of hulls. When placed in contact with water, the treenails swelled and held tighter than iron rivets; moreover, they did not rust when in contact with salt water. It has been estimated that between 50,000 and 100,000 black locust tree “nails” were exported annually from Philadelphia alone during the early 1800s.

In this region, black locust was highly prized by the Cherokees and early settlers. It was so useful, in fact, for blowgun darts, bows, “nails,” and other items they planted and cultivated the rapidly growing tree. The early settlers had numerous other uses for the rot-resistant wood, especially as base logs and interior beams for houses or outbuildings, firewood, and as durable fence posts. Farmers in some areas have planted locust groves for the purpose of providing fenceposts. Since the tree grows two-to-three feet per year and sends up suckers from its roots, a small grove could supply a lot of posts.

Let’s close with the following observations made by M. Pepin, principal of the School of Botany at the Jardin du Roi in Paris, published in the issue of Scientific American for Jan. 9, 1847, as well as other periodicals.

A number of black locust trees were felled that had been planted from 40 to 50 years; but not more than one to five of those wheelwrights [makers of wheels] who came to purchase, appreciated sufficiently the locust, the others preferring elm. Ultimately, the locust was sold to the persons who knew its value, at one-third higher price than the elm. The purchasers found that spokes made of the wood in question lasted two sets of “felloes” [wheel rims], and were likely to answer for a third. Under equal circumstances of wear and tear, spokes made of locust wood were perfectly sound, while those of oak required to be replaced.

 

It is the most durable of all our hardwoods;

taking white oak as the standard of 100 percent,

black locust has a durability of 250 percent.

— D.C. Peattie, A Natural History of Trees

 

(George Ellison can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. )

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