Acacia Mill.

Faidherbia albida is the only species within this genus. Its distribution is over drier parts of southern sub-Saharan Africa (chiefly tropical and East Africa); in South Africa the taxon is confined to watercourses in northern KwaZulu-Natal, Mpumalandga and the Limpopo Province. In 2010, C.Michael Hogan has located the species along some of the seasonally dry riverbeds in the western-central Namib Desert, where it is a favourite food source of the Desert Elephant.

This tree is 40-80' tall at maturity, forming a trunk about 1½-3' across and an irregular crown with spreading to ascending branches. Trunk bark is variable, depending on the age of a tree; young trees have brown bark that is slightly rough and shallowly furrowed, while older trees have thick gray bark that is very rough and deeply furrowed with forking ridges. The bark of branches is gray to brown and more smooth, while twigs are brown to reddish brown, smooth, and glabrous with scattered white lenticels. Pairs of stout thorns about ¼-½" long occur along the twigs and branches near the axils of former leaves. Young shoots are light green and slightly pubescent. Alternate compound leaves about 6-14" long occur along the twigs and shoots; they are odd-pinnate with 7-19 leaflets. The stalks and leaflets of young compound leaves may be slightly pubescent, but they become glabrous with age; they are initially yellowish green. At maturity, individual leaflets are 1-2" long and ½-¾" across; they are medium green or blue-green, oblong or oblong-elliptic in shape, and smooth along their margins. Each leaflet has a tiny bristle-like tip, while at its base there is a short petiolule (basal stalklet) less than 1/8" long. The flowers are produced in drooping racemes about 4-6" long. The central stalk and pedicels of each raceme are pale green and glabrous to slightly pubescent. Individual flowers are ¾-1" long, consisting of 5 white petals, a tubular calyx with 5 teeth, several hidden stamens, and an ovary with a single style. The petals are arranged in a pea-like floral structure consisting of an upright banner and a pair of forward-projecting wings that enclose a keel. There is a small patch of yellow at the base of the banner. The calyx is light green, yellowish green, or pinkish green; it is either glabrous or slightly pubescent. The blooming period occurs from late spring to early summer for about 2 weeks after the leaves are fully developed. The flowers have a strong sweet fragrance. Afterwards, fertile flowers are replaced by drooping seedpods that become 2-4" long at maturity during the autumn. Mature seedpods are dark brown, oblongoid in shape, flattened, and either straight or slightly curved; each seed pod contains 4-14 seeds. The seeds are a little less than ¼" long, reniform in shape, dark brown, and somewhat flattened. They are dispersed primarily by gravity, falling to the ground not far from the mother tree. The woody root system produces lateral roots that are usually shallow and widely spreading, although at dry sites it can develop a taproot with deep lateral roots. The root system also produces long underground runners, from which clonal offsets are produced. As a result, this tree often occurs in clonal colonies. The deciduous leaves usually turn yellow during the autumn.

More info for the terms: cover, density, hardwood, presence

Black locust seeds may persist in the soil for long periods of time. A Michigan flora states that seeds may survive for more than 88 years in the soil [329]. In a laboratory study, seed from 107 plant species was buried up to 42 inches (107 cm) in soil. Black locust was 1 of 16 plant species with more than 15% of seeds viable after 39 years [316]. Other sources state that seeds remain viable for more than 10 years ([325], review by [26]) or "many" years [87,113]. In mixed-oak and northern hardwood forests of western North Carolina, black locust seeds remained viable in the soil for more than 1 year. Soil seed densities were higher than seed rain, suggesting low annual seed mortality and the presence of seeds from previous years [155].

Because black locust seeds are persistent, they may accumulate to great levels in the seed bank. In Hungary, seeds accumulated over decades in the top 4 inches (10 cm) of soil (review by [181]). In a second-growth mixed-hardwood forest in Great Smoky Mountains National Park, black locust seeds were found in the soil at a density of 29,817 seeds/acre (73,680 seeds/ha) [118]. In contrast, in a mature mixed-oak-maple forest in southwest Virginia, black locust seeds were found at a density of only 121 seeds/acre (300 seeds/ha). The authors suggested that the continuous cover of mature forest would make it difficult for early-successional species like black locust to produce a large quantity of seeds [285].

More info for the terms: cover, hardwood, presence, tree

Though often considered poisonous to livestock, black locust is grown in some areas specifically as livestock forage. Black locust provides food and structural habitat for a variety of wildlife species.

Palatability and/or nutritional value: Numerous accounts describe parts of the black locust as poisonous to livestock including mules (review by [69]), horses ([136,313], review by [69]), cattle [136,303,313], and domestic sheep ([313], review by [69]) due to the presence of the poison robotin [136]. Poisonous plant parts include the roots [303], young shoots ([136,303,313], review by [98]), seeds [85,153,190,258,313], twigs [113], leaves [85,153,258], and bark ([85,113,136,153,258,313], review by [98]). In some cases, poisoning may be fatal to livestock ([136,153], review by [69]), though one author asserts that fatality from poisoning is rare [313]. In livestock, symptoms of black locust poisoning may include reduced hearing, stupor, vomiting, and purging (review by [98]).

Despite the potential for black locust poisoning and its classification in one guidebook as worthless to poor forage for livestock (review by [69]), black locust is used as livestock feed in parts of its introduced range. It is grown to feed domestic goats in northern Pakistan [10], domestic sheep and goats in New Zealand [193,249], and general livestock in Bulgaria and Korea (review by [181]). In Mendocino County, California, chickens were observed eating black locust seeds, and horses ate the leaves sparingly [57]. In North Carolina, domestic goats and cattle defoliated black locust shoots in an abandoned orchard. The level of browsing was substantial enough to kill all black locust after 4 years of browsing [206].

Black locust is a food item for many wildlife species. White-tailed deer heavily browse black locust in North Carolina, [79], Georgia [141], and Arkansas (review by [69]), though one study found a lack of white-tailed deer herbivory on black locust in Maryland and West Virginia [139]. Mule deer browse black locust in Washington [50], California ([199], review by [132]), and New Mexico (review by [191]). Rabbits browse on stems ([188], review by [263]). Ruffed grouse eat black locust leaves [348]. Squirrels ([313], reviews by [69,312]), doves [320], California quail (review by [132]), northern bobwhite ([110,138,170,275], review by [312]), chukar (review by [132]), pheasants ([303], review by [312]), ruffed grouse [348], and other game birds ([303], review by [312]) eat black locust seeds.

Invertebrate species also consume black locust. Freshly fallen black locust leaves were palatable to millipedes in laboratory studies [207]. Black locust was a host to the Lepidopteran species the silver-spotted skipper and the three-staff underwing in the southeastern United States [320], and it is widely visited by bees for its nectar throughout its native and nonnative ranges ([313], review by [167]).

Nutritional content: Black locust seeds are high in crude protein ([253,258], review by [312]), phosphorus ([253], review by [312]), and crude fats and low in calcium (review by [312]). Black locust leaves had the highest nitrogen content of any tree tested in a North Carolina mixed-oak-hardwood forest [75]. Five- to 10-year-old black locust in a western North Carolina mixed-oak and cove hardwood forest had significantly higher leaf nitrogen than the other 7 dominant species tested (P=0.0001). Along with yellow-poplar, black locust also had higher leaf potassium and phosphorus compared to other species (P=0.0001) [103].

Humans: Black locust is poisonous to humans [85,153,313]. In some cases, poisoning may be fatal [153]. Symptoms of black locust poisoning include dilated pupils, feeble pulse, severe vomiting, and a death-like pallor [136]. Humans may get dermatitis from exposure to black locust wood [3].

Some people eat fried or cooked black locust flowers [303,313]. Tea can be made from the flowers [313].

Cover value: Black locust is an important cover species for wildlife (review by [167]), providing nesting, roosting, and thermal cover. The persistent nature of black locust stems after plant death makes it an important resource for cavity-dependent wildlife species [248]. A disproportionate number of snags were identified as black locust in a Maryland old-growth forest remnant [88], a 24- to 64-year-old yellow-poplar-red maple stands in southeast Ohio [92], and second- and old-growth mixed-hardwood forests in eastern Kentucky [220]. Compared to surrounding forest, a disproportionate number of cavities were found in black locust trees in mixed-hardwood [177] and oak-hickory [48] forests in West Virginia.

Black locust cavities are used for nesting and roosting by bats and birds. Black locust cavities were used as maternity roosts for long-eared bats in West Virginia [228,248] and the endangered Indiana bat in the Champlain Valley [336], and as day roosts for male northern bats in West Virginia [115]. In its native range, black locust provides nesting cavities for birds such as the hairy woodpecker [65], downy woodpecker [65], northern flicker [65,219] and red-bellied woodpecker [219]. In Kentucky, eastern screech-owls roosted in black locust cavities in the winter [96].

Black locust cover is also important to birds. Black locust was positively associated with red-eyed vireo habitat in southwestern Virginia [163] and rufous-sided towhee habitat in Maryland [119]. In a mixture of small deciduous woodlots and thickets interspersed with old fields in Kentucky, adult and juvenile eastern screech-owls used black locust stands for roosting in the postfledging period [18].

Outside of the native range of black locust, birds that nest in black locust foliage include the black-billed magpie, western kingbird, Baltimore oriole [28], and Swainson's hawk in eastern Washington [14,28], the long-eared owl [212] and loggerhead shrike in Idaho [358], and the dickcissel in central Oklahoma [247]. Near Cape Cod, Massachusetts, black locust stands provided suitable cover for northern bobwhite and American woodcock [275]. In south-central Kansas, 62 breeding bird species were detected in shelterbelts containing black locust [287], and black locust was highly recommended for planting as wildlife habitat in the Northern Great Plains region (review by [148]).

Black locust occurring in small (0.52 acre (0.21 ha)) to large (8.92 acre (3.61 ha)) patches in the Palouse prairie region of eastern Washington and northern Idaho provided winter thermal, loafing, and hiding cover for 7 mammal species (moose, white-tail deer, coyote, North American porcupine, striped skunk, house cat, and mountain cottontail), 23 avian species (including gray partridge, ring-necked pheasant, red-tailed hawk, rough-legged hawk, great-horned owl, and short-eared owl), and 1 reptile (garter snake) [32].