Black locust (Robinia pseudoacacia): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table.

At a glance

Item	What the source records
Scientific name	Robinia pseudoacacia L., legume family (Silvics)
Other names	Yellow locust (Silvics and Wood Handbook)
Native status, USDA PLANTS	Native in the lower 48 states; introduced in Canada
Size, Silvics	Generally 12 to 18 m (40 to 60 ft) tall and 30 to 76 cm (12 to 30 in) in diameter; on better sites 30 m (100 ft) and 122 cm (48 in) or more
Green weight of the wood, NRS-38	58 lb per cubic foot, without bark

Native range and naturalized spread

The Silvics of North America handbook (Agriculture Handbook 654, 1990) says black locust has a disjunct original range whose extent is not accurately known. The eastern section is centered in the Appalachian Mountains, from central Pennsylvania and southern Ohio south to northeastern Alabama, northern Georgia and northwestern South Carolina. The western section covers the Ozark Plateau of southern Missouri, northern Arkansas and northeastern Oklahoma and the Ouachita Mountains of central Arkansas and southeastern Oklahoma. The handbook says the tree has been planted widely and has become naturalized throughout the United States, southern Canada and parts of Europe and Asia, and that it has been successfully introduced into many parts of the world with different climates.

Silvics says the species does best on moist, rich, loamy soils or soils from limestone, and thrives on moist slopes of the eastern mountains below 1,040 m (3,400 ft). It is very sensitive to poorly drained or compact plastic soils, and excessively dry sites are also poor for it. It grows on a wide variety of disturbed sites such as old fields. The handbook describes it as a pioneer type, usually man-influenced and temporary: it makes up the majority of a stand in early stages but is short lived and seldom matures to a sawtimber stand. It names one forest cover type for it, Black Locust (Society of American Foresters Type 50).

Flowers, pods and suckers

Silvics says fragrant, whitish flowers in showy racemes appear after leaf emergence in May or June and are pollinated by insects, primarily bees. The fruit is a flattened, oblong pod that ripens in September and October and opens on the tree, with seeds dispersed from September to April. The tree begins seed production at about age 6 and produces good crops at 1 to 2 year intervals, best between 15 and 40 years. Seed coats are impermeable. The handbook says black locust sprouts readily from stump and roots, especially after being cut or damaged, that root suckers are the most common form of natural reproduction, and that dense thickets of suckers develop in clearcuts in the southern Appalachians.

Growth and roots

The handbook says young trees grow very fast on good sites but the species matures early and growth rate falls rapidly after 30 years, and that on better sites the trunk is often clear and straight while the trunk of an open-grown tree is usually short and divides at 3 to 5 m (10 to 15 ft) into several stout branches. It classes the tree as very intolerant of shade. The root system is ordinarily shallow and wide spreading, which it calls excellent for soil binding, but is also capable of deep roots: in the arid Southwest trees may develop vertical roots 6.1 to 7.6 m (20 to 25 ft) long. Radial root spread is about 1 to 1.5 times tree height.

Uses the sources record

Silvics says black locust is not an important timber tree in the United States but is planted for erosion control, reclamation of mine spoil and other disturbed sites, windbreaks, honey production and ornament, and that it fixes nitrogen. It lists fence posts, mine timbers, poles, railroad ties, insulator pins, ship timber, tree nails, boxes, crates, pegs and stakes among its wood products, and says it is suitable for fuelwood and pulp. The Wood Handbook (FPL-GTR-282, 2021) describes narrow creamy-white sapwood and heartwood that varies from greenish yellow to dark brown when freshly cut, calls the wood heavy, hard, resistant to shock, strong and stiff with moderately low shrinkage, and says the heartwood has high decay resistance. The handbook records the greatest timber production in Tennessee, Kentucky, West Virginia and Virginia and says the IUCN considers black locust a species of least concern.

Wood Handbook figure	Green	At 12% moisture content
Specific gravity (Table 5-3b)	0.66	0.69
Modulus of rupture, lbf per square inch (Table 5-3b)	13,800	19,400
Side hardness, lbf (Table 5-3b)	1,570	1,700

The green weight is in the NRS-38 table, the same figure used in the log weight calculator.

Damaging agents the handbook names

Silvics says black locust is severely damaged by insects and disease, probably more than any other eastern hardwood species.

Locust borer. The handbook says attacks by the locust borer and by the heart rot fungi Phellinus rimosus or Polyporus robiniophilus are ubiquitous and make growing black locust for timber impractical. Borer larvae tunnel throughout the wood, and the holes serve as entry points for the rot fungi. It says slow-growing trees on poor sites are the most susceptible and that repeated attacks can reduce the tree to sprout clumps.
Other insects. The locust leafminer, whose outbreaks the handbook says occur almost yearly and can defoliate trees across a whole region, and the locust twig borer, which can cause high seedling mortality in heavily infested areas.
Diseases. Heart rot, which the handbook says infects most large trees in the southern Appalachians, witches' broom disease caused by a virus, and extreme susceptibility to Phymatotrichum omnivorum in the Texas root-rot belt. In New Brunswick it records high mortality and branch dieback from Nectria cinnabarina.
Cold. Moderately frost hardy in the southern and central Plains but highly susceptible to frost damage in the Appalachian region.

Silvics also says most forest managers outside reclamation consider the tree a weed species and a strong competitor with more desirable species, and that it has been found to be a useful nurse crop for some trees on mine spoil and not for others. For who takes reports of regulated pests, see reporting a pest in the United States, and pests and diseases by country sets out which ones agencies regulate.