LOCUST
(Robinia Pseudacacia)

Locust belongs to the pea family, known in botany as LeguminosÆ.[6] In most parts of its range it is known simply as locust, but in some localities it is called black locust, an allusion to the color of the bark; yellow locust, descriptive of the heartwood; white locust, referring to the bloom; red locust, probably a reference to the wood, and green locust for the same reason; acacia and false acacia; honey locust, a name which belongs to another species; post locust, because it has always been a favorite tree for fence posts; and pea-flower locust, a reference to the bloom.

Several of the names refer to the color of the wood, and seem contradictory, for yellow, green, and red are not the same; yet the names describe with fair accuracy. Color of the heartwood varies with different trees, yellow with some, tinged with red with others, and sometimes it might be appropriately called blue locust, for the heartwood is nearer that color than any other.

The natural range of locust seems to have been confined to the Appalachian mountain ranges from Pennsylvania to Georgia. It probably existed as a low shrub in parts of Arkansas and Oklahoma. Its range has been extended by planting until it now reaches practically all the states, but is running wild in only about half of them. It has received a great deal of attention from foresters and tree planters. It attracted notice very early, because of its hardness, strength, and lasting properties. At one time the planting of locust came nearly being a fad. In England it was supposed that it would rise to great importance in shipbuilding, and in France it was looked upon as no less important. Books were written on the subject in both English and French. All the details of planting and utilization were discussed. Its generic name, Robinia, is in honor of a Frenchman, Robin. Extravagant claims were once made for the wood. When American ships were gaining victory after victory over English vessels in the war of 1812, it was asserted in England that the cause of American success was the locust timber in their ships. The claim may have been partly true, but other factors contributed to the phenomenal series of successes.

The locust craze died a natural death. Too much was claimed for the wood. Possibilities in the way of growth were over estimated. It was assumed that the tree, if planted, would grow everywhere as vigorously as on its native mountains in Pennsylvania, Maryland, and Virginia, where trees two or three feet in diameter and eighty feet high were found. Experience proved later that nature had planted the locust in the best place for it, and when transplanted elsewhere it was apt to fall short of expectations. Outside of its natural range it grows vigorously for a time, and occasionally reaches large size; but in recent years the locust borer has defeated the efforts of man to extend the range of this species and make it profitable in regions distant from its native home. The tree is often devoured piecemeal, branches and twigs breaking and falling, and trunks gradually disappearing beneath the attacks of the hungry borers. No effective method of combating the pest is known. The planting of locust trees, once so common, has now nearly ceased.

Within its native range, and beyond that range when it has a chance, locust is a valuable and beautiful tree. It is valuable at all times on account of the superior wood which it furnishes, and beautiful when in bloom and in leaf. A locust in full flower is not surpassed in ornamental qualities by any tree of this country. It is a mass of white, exceedingly rich in perfume. It blooms in May or June. During the summer its foliage shows tropical luxuriance with exquisite grace. Its compound leaves are from eight to fourteen inches long, with seven to nine leaflets. They come late in spring and go early in autumn. The tree’s thorns, resembling cat claws, are affixed to the bark only, and usually fall with the leaves. The fruit is a pod three or four inches long, and contains four or eight wingless seeds. They depend on animals to carry them to planting places. The pods dry on the branches, and rattle in the wind most of the autumn. The tree spreads by underground roots which send up sprouts. A locust in winter is not a thing of beauty. It appears to be dead; not a bud visible. Its black, angular branches lack every line of grace.

Locust wood is remarkable for strength, hardness, and durability. It is about one pound per cubic foot lighter than white oak, but is thirty-four per cent stiffer and forty-five per cent stronger. Its strength exceeds that of shagbark hickory, and it is doubtful whether a stronger wood exists in the United States. Its hardness is equally remarkable, and is said to be due to crystals formed in the wood cells, and known as “rhaphides.” Its durability is probably equal to that of Osage orange, mesquite, and catalpa, but it is not easy to fix a standard of durability by which to compare different woods. Locust is the best fence post wood in this country, because it is usually much straighter than other very durable woods. The posts are expected to last at least thirty years, and have been known to stand twice that long.

For more than 150 years locust was almost indispensable in shipbuilding, furnishing the tree nails or large pins which held the timbers together. It supplied material for other parts of ships also, but in smaller quantities. The substitution of steel ships for wooden lessened demand for locust pins, and in many instances large iron nails are used to fasten timbers together. In spite of this, the demand for locust tree nails is nearly always ahead of supply.

The wood’s figure is fairly strong, due to the contrast between the springwood and that grown later, but not to the medullary rays, which are small and inconspicuous. The wood is not in much demand for ornamental purposes. Small amounts are made into policemen’s clubs, rake teeth, hubs for buggy wheels, ladder rungs, and tool handles.

The tree grows rapidly where conditions are favorable, and very slowly when they are not. Usually trees of fence post size are twenty years old at least, but trunks thirty five years old have been known to produce a post for each two years of age, though that was exceptional. Railroads, especially in Pennsylvania, planted locust largely a few years ago for ties. It has been reported that in some instances expectations of growth have not been fully realized.