Black locust

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Black locust (Robinia pseudoacacia), also known as Yellow locust, Locust, Acacia, or False Acacia, and, sometimes as post oak, is a deciduous tree of the legume family which is native to the Appalachian, Ozark and Ouachita mountain ranges. Because it grows quickly in open areas with dry soil, and develops large amounts of hard, strong timber it has been planted widely and has become naturalized in temperate zones around the world. It is also popular as an urban tree due its tolerance for poor soils and air pollution.

The tree's common name was given to it by English settlers at Jamestown, Virginia, who likened the appearance of its seed pods to the European locust or carob tree. Black locust trees typically grow to 40 to 100 feet tall, with red-brown deeply-furrowed and cross-checked trunks 2 to 4 feet in diameter with a sinuous growth. Major limbs tend to grow upward rather than outward, and smaller branches tend to zig-zag, creating a relatively narrow crown, which becomes markedly ragged with age. The compound leaves appear in late spring, each bearing 9-13 leaflets which are darker on top than underneath, giving the foliage a shimmering effect in light breezes. The leaves fold inward during night and rain. In autumn the leaves fade to a pale yellow color and the orange-brown hanging seed pods ripen. Large clumps of fragrant white flowers appear briefly, after the leaves, in late spring. Seed and leaf production can be irregular, with "good crops" appearing at 1-3 year intervals.

The nectar is prized by apiarists who market "Acacia honey". Young saplings grow defensive spines, but they disappear with age, in contrast with the similar looking Honey locust (which, ironically, is not a major honey plant). In some parts of Europe and Asia the flowers are used to make jam or fried and eaten by themselves. The seeds are edible as well, but are small and dry and require a great deal of labor to remove from their pods. The bark, wood and leaves are toxic to humans and livestock.

Black locusts reproduce both sexually, via its pollinated seeds, and asexually, via shoots or suckers which grow from the trunk or from the shallow bed of roots. Local propagation by root suckers enable individual trees to form dense stands over time. Over longer periods, clusters may extend along seams of preferred soils. In mixed forest environments, other species tend to outcompete shade-intolerant black locust seedlings over time. Like other legumes, black locust roots are able to fix nitrogen in soils. Animals may use the tree for cover, and eat the seeds in winter. It is targeted by the locust leaf miner and locust borer beetles, and is also susceptible to fungal rot and viral attacks which manifest as tangles of shoots commonly called "witch's brooms". Those vulnerabilities limit the prospect of planting black locust commercially for lumber.

Nevertheless, the wood from black locusts, when not diminished by insects, is valued because it is very dense and hard and resists rot. Typical uses include fence posts, ship timbers, mine timbers, rail ties, crates, pins, pegs, rungs, handles, clubs, rake teeth and stakes. Zig-zagged branches are sometimes collected and worked into ornamental railings. It is also a desirable firewood for its slow, hot, burn with minimal smoking.

In the Birmingham area, the Locust Fork River is named for the black locust trees found along its banks. The laminated timbers and wood siding at the pavilion at Railroad Park are black locust.

References

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