Robinia pseudoacacia
Morphology:
Phanerophyte
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Plants
Robinia pseudoacacia L.
EOL Text
Miscellaneous Details:
"Notes: Western Ghats, High Aaltitude, Cultivated, Native of North America"
Diagnostic:
Habit: Tree
Seedling establishment and plant growth:
More info for the terms: density, hardwood, natural, reclamation, tree
Establishment: Black locust requires open conditions for establishment ([252,297], reviews by [167,314]). Establishment is often linked to natural ([37,164], review by [167]) and manmade ([99,103,285], review by [167]) disturbances. See Successional Status for more information on this topic.
Growth rate: Black locust is known for its rapid juvenile growth rate ([24,59,126,137,202,291,361], review by [167]). In mixed-oak, cove, and northern hardwood forests in North Carolina, the 5-year average radial growth rate for black locust was 1.31 mm/yr, which was the highest of the 7 species tested [361]. The growth rate of black locust seedlings is limited by plant density ([120], review by [167]) and insect infestations [120,365] and enhanced by light [164], moisture [23,185], and fertilization [23,365].
In its native range, black locust grows rapidly following disturbances such as logging or mining. In regenerating hardwood forests in North Carolina, black locust seedlings grew 26 feet (8 m) in 3 years. They grew faster than any other species for 10 to 20 years [24]. Black locust had the second-tallest mean height of dominant hardwood species 5 years after clearcut treatments in mixed-oak stands in Virginia, with trees as tall as 8.6 feet (2.6 m) [364]. After overstory removal in Pennsylvania mixed-oak stands, black locust seedlings were 3.4 feet (1.0 m) tall 1 year after treatment and 8.1 feet (2.5 m) tall 4 years after treatment [126]. On limestone and acid-shale mine sites in Ohio, direct-seeded black locust reached an average height of 25 feet (8 m) in 7 years, which was higher than any other plant species [202].
Black locust growth rates are also high in its nonnative range. A review states that black locust growth rates in plantations in the central states could average as much as 42 feet (12.8 m) in 10 years, 68 feet (20.7 m) in 25 years, and 84 feet (25.6 m) in 40 years [167]. In experimental old-field rehabilitation plantations in Iowa, 12- to 15-year-old black locust had the highest annual height growth (µ=2.47 feet (0.75 m)) of any species planted [137]. On mine reclamation sites in southeast Kansas, black locust had the fasted growth of all planted species, growing 23 feet (7 m) in 10 years [291].
Density: Black locust may grow at high or low densities depending on local site characteristics. Within its native range, seedling densities are variable. There are often few seedlings under canopies containing mature black locust [172,297]. Black locust seedling density was 125 seedlings/ha in an old-growth mixed-hardwood forest in West Virginia [2]. In contrast, in the Nantahala National Forest in North Carolina, oak-hickory-poplar forest gaps created by clearcutting contained numerous black locust seedlings (3,854 seedlings/ha) and sprouts (2,616 sprouts/ha) 2 years after treatment [297].
Within mature forests of its native range, black locust usually occurs as a canopy tree at low density [1,2,7,40,47,88,92,106,172,205]. For example, there were significantly more black locust stems in 35-year-old, second-growth (22.3 stems/ha) compared to old-growth (4.1 stems/ha) mixed-hardwood forest in eastern Kentucky (P<0.05) [220]. See Successional Status for more information.
In its nonnative range, black locust trees may establish in high densities outside of plantation settings ([231,252], reviews by [72,226]). In a disturbed forest regenerating after a horticultural area was abandoned in New York, black locust established 97 stems/acre (240 stems/ha) in the 8- to 12-inch (20-30 cm) size class and 32 stems/acre (80 stems/ha) in the 12- to 16-inch (30-40 cm) size class in 20 to 40 years. Black locust also dominated the seedling and sapling layer of a mixed-oak dry forest, occurring at a density of 898 stems/acre (2,220 stems/ha) in the 0- to 1-inch (0-2.5 cm) size class [260]. In a pine barrens community near Albany, New York, black locust occurred in nearly pure patches covering 1.2 to 12 acres (0.5-5 ha); these patches were surrounded by pitch pine and scrub oak [231]. In restored oak savanna and woodland sites in Minnesota, black locust stem densities ranged from 4 to 400 stems/acre (10-1,000 stems/ha), with some areas completely dominated by black locust (Kruger personal communication cited in a review [283]).
Seed Production:
Black locust begins seed production at about age 6 and produces good crops at I- to 2-year intervals. Seed production is best between 15 and 40 years of age and continues until age 60. Black locust yields 7 to 15 kg (15 to 33 lb) of seeds per 45 kg (100 lb) of fruit, and seeds average 52,900/kg (24,009/lb) (34,37).
Special Uses:
Although black locust is not an important timber tree in the United States, it is used for a wide variety of products and is planted for many specialized purposes. It is used for fence posts, mine timbers, poles, railroad ties, insulator pins, ship timber, tree nails for wooden ship construction, boxes, crates, pegs, stakes, and novelties. Pulp with satisfactory mechanical properties can be made, particularly by the sulfate process (35). It is also suitable for use in fuel plantations (14,16).
Black locust is widely planted in the United States, Europe, and Asia for erosion control, reclamation of drastically disturbed sites, windbreaks, nurse crops, amelioration of sites, honey production, and ornamental use. Many early plantations on severely eroded old fields were failures, but establishment on spoil banks has been generally successful. Black locust is often broadcast or hydroseeded with a mixture of herbaceous seed. The most commonly used seeding rate is 2.2 to 3.4 kg/ha (2 to 3 lb/acre) (12).
Because of its soil-improving properties, black locust is often planted in mixtures. Many species have been underplanted in black locust stands. Success of such planting has been variable and many factors have to be considered carefully (37). On mine spoil in Illinois, black locust was a valuable nurse crop for black walnut (Juglans nigra), silver maple (Acer saccharinum), and yellow-poplar (Liriodendron tulipifera), but not for cottonwood (Populus deltoides), sweetgum (Liquidambar styraciflua), or Osage-orange (Maclura pomifera) (25). On surface-mined land in Kansas, survival, growth, and form of black walnut were impaired when planted with black locust (39).
Black locust was superior to other hardwoods in developing wildlife habitat on mine spoils. It quickly provided cover, and by 10 to 15 years native vegetation had established a dense undergrowth (36). Its seeds are rated low as wildlife food but are used to a limited extent by Northern bobwhite, other game birds, and squirrels (30,42). White-tailed deer browse the young growth, and a study in the southern Appalachians showed that 92 percent of the sprouts were browsed (13). Because older trees are usually infected with heart rot, woodpeckers often construct cavities in them. Nest cavities of the downy woodpecker, hairy woodpecker, and common flicker have been found (9).
Description:
Black locust has a shallow, aggressive root system. The bark of black locust is deeply furrowed and is dark reddish-brown to black in color. It has an alternate branching pattern, which creates a zigzag effect. A pair of sharp thorns grows at each node. They are ½ to ¾ inches long, and very stout.
The pinnately compound leaves are 8 to 14 inches long, with 7 to 19 short stalked leaflets. These dull green leaflets are ovoid or oval, 1 to 2 inches long, thin, scabrous above and pale below.
The separate male and female plants have sweetly fragrant flowers that are creamy white with five petals (bean-like) arranged in a pyramidal spike. They usually bloom in May or June. Heavy seed production can be expected annually or biannually. The legume type seed is produced in a flat, brown to black pod, which is 2 to 4 inches long. There is an average of 25,500 seeds per pound. Although black locust is a good seed producer, its primary means of spread is by both rudimentary and adventitious root suckers.
Holotype for Robinia pringlei Rose
Catalog Number: US 462258
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): C. G. Pringle
Year Collected: 1906
Locality: Valley near Tula., Hidalgo, Mexico, North America
Elevation (m): 2073 to 2073
- Holotype: Rose, J. N. 1909. Contr. U.S. Natl. Herb. 12: 274.
| License | http://creativecommons.org/licenses/by/3.0/ |
| Rights holder/Author | This image was obtained from the Smithsonian Institution. Unless otherwise noted, this image or its contents may be protected by international copyright laws. |
| Source | http://collections.mnh.si.edu/search/botany/?irn=2093593 |
Germination:
Black locust seeds require scarification ([325], reviews by [167,181]) and bare mineral soil ([164,216], review by [314]) for successful germination. Though one source cites germination rates as high as 68% in its native range [325], most sources suggest that seed germination is low (review by [131]) due to high seed coat impermeability ([252], review by [226]) and shade intolerance [164,252]. Direct-seeded black locust on limestone and acid-shale sites in Ohio had low germination rates, ranging from 3% to 17%. Survival of these germinants ranged from 23% to 78% [202]. Fifteen to 33 days after planting in a greenhouse, fall-collected black locust seeds from New Haven, Connecticut, exhibited 45% germination. The addition of various salt concentrations delayed and slightly lowered percent germination [19].
In greenhouse trials, black locust seeds germinated uniformly over a 5-week period [87].
Flowering and Fruiting:
The fragrant, whitish flowers, borne in showy racemes, appear after leaf emergence in May or June. The perfect flowers originate in the axils of current year leaves and are pollinated by insects, primarily bees. The fruit is a flattened, oblong pod that ripens during September and October. The fruit opens on the tree and seeds are dispersed from September to April (34).
Uses:
Since the wood of black locust is strong, hard, and extremely durable, it is extensively utilized for fencing, mine timbers, and landscaping ties. This tree also serves as a good erosion control plant on critical and highly disturbed areas, due to its ease of establishment, rapid early growth and spread, and soil building abilities. It has limited value in wildlife food plots, but provides excellent cover when planted in spoil areas. Due to its showy aromatic flower, it has often been planted as an ornamental, but this practice should be discouraged due to the potential for spread by root suckers. This species has been planted outside its natural range, and can crowd out other plants, particularly in sandy soils.