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Black locust the fantastic Tree

Following info. from The-Tree.org.uk: Friendly, enjoyable place for people who love trees.

Family: Leguminosae (Pea family), subfamily Papilionoideae

Synonyms: Black Locust, Locust Tree, Robinia (navne på træ der holder)

Black Locust was one of the earliest North American trees to have reached Europe. The first known was in the garden of Jean Robin, herbalist to the King of France. It was introduced to Britain in the 1630’s and it has naturalised in some places. It is locally common in the Southern half of England as a street, garden and park tree.
Britain gained over a million Black Locust trees in the early 1800’s after William Cobbett, author of the English gardener, journalist and rural reformer returned from a trip to the New Country full of missionary zeal about the excellence of the tree.

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Cobbett was so impressed with Robinea pseudoacacia that he predicted that it would replace all the British hardwoods then in cultivation. Quick growth was seen as a huge advantage over the very slow growth of quality timber from an Oak.
Maybe Cobbetts enthousiasm may also have been fired by the extensive nurseries he had established at Kensington and Barnes to flood the country with these miracle trees. Many people bought his trees at inflated prices, but sadly their quality as a perfect timber tree left much to be desired, as Cobbett had not selected his seed sources with enough care and most of them became crooked trees stiff- limbed zig-zaggy branches. The bare branches could be admired for much of the year, because as one critic of the tree said: They are only in leaf for about a fortnight…..
That is of course massively exaggerated but it’s true that Black Locust does come into leaf relatively late and is early to shed its foliage again.

William Cobbett was by no means the first Englishman to discover the special qualities of the Black Locust tree nor the only one to feel passionately about it. The debate about its virtues and ‘vices’ in Britain (and elsewhere) goes a long way back. Here are just two other English examples:
The famous English arborist Evelyn wrote about the tree in his classic work “Sylva”, published in 1664: “By reason of its brittle nature, it does not well resist . . . our high winds; and the roots, which insinuate and run like liquorice under ground, are apt to emaciate the soil, and, therefore, haply not so commendable in our gardens as they would be agreeable for variety of walks and shade. They thrive well in His Majesty’s new plantation in St. James’s Park.”
Ebenezer Jessup wrote an article in 1791 in the Gentleman’s Magazine proposing that ten thousand acres in the New Forest and Forest of Dean should be planted with False Acacia to be used for navy shipbuilding. He also stating that he knew posts made of its wood to last from 80 to 100 years.

“Robinia” is named after Jean Robin, in whose garden the tree was first grown in Europe.

“Pseudoacacia” means ‘False Acacia’ and comes from the similarities between this tree and the Acacia’s (also members of the Pea family) which grow in Australia, Africa, etc. To add to the confusion we call these real Acacia’a: Mimosa or Wattle.
The actual word ‘Acacia’ derives from the Greek ‘akis’ meaning ‘thorn’.

‘Locust Tree’ is a name given to Robinia pseudoacacia (and its close relative Gleditsia triacanthos) by some of the 17th century religious immigrants to America.
The Bible tells the story of how John the Baptist was kept alive in the wilderness by eating ‘locusts’, which were not the insects, but the pods of the Carob tree, which have some resemblance to the beasties. Carob (Ceratonia siliqua) is an evergreen member of the Pea family, which grows in hot dry areas and whose lavender-brown pods contain 10-16 glossy seeds in a sweet pulp, which is very nutritious and tastes rather like chocolate!
When the Christian immigrants discovered Robinia and Gleditsia, who were also members of the pea family and which has roughly similar pods, they were called the “Black Locust” and the “Honey Locust” respectively.

Habitat: Originally native in the Appalachian Mountains (below 3500 feet) from central Pennsylvania south to northern Alabama and Georgia in the East USA and also in southern Missouri, north and west central Arkansas, eastern Oklahoma, southern Illinois and southwestern Indiana.
An excellent reputation for good hard wood, combined with fast growth and its popularity as a street tree has contributed to the spread of the Black Locust to be cultivated throughout the world. It seems to thrive on a wide range of soils and can cope with much drier climates than it finds in the regions of its origin. It has been planted and is naturalized north to Nova Scotia, Quebec and Ontario, it grows well in places like Cyprus and Israel and it has been widely used as a forest tree in East European countries. It has also been grown extensively in China, Korea, the Himalayas and New Zealand. As if this huge range from temperate to subtropical does not suffice, the tree has also been grown in some of the upper cooler regions of tropical Java!

When forest-grown, False Acacia can produce clear, straight trunks, but depending on inherited tendencies it may tend to fork and be crooked when grown in an open position.
The tree has sharp spines, which are found at the nodes of young branches but are rare on mature wood.
The brown or grey bark is furrowed and these grooves are often twisted.
The foliage is light green or yellowish-green with alternate feathery (pinnate) leaves. Each leaf consists of a midrib with 4 to 9 pairs of small leaflets (oval/ovate and 2.5 to 5 cm long) and a leaflet at the tip.
A few weeks after the leaves first appear the pea-like hermaphrodite flowers come out in May/June. They have a sweet vanilla-like scent, are creamy white and hang in drooping clusters.
After being fertilised by insects, especially bees, the fruits develop into smooth brown flattish pods (10-15cm) with 4-8 black seeds. They ripen in September/October and remain on the tree until they split into two and are carried off (with seeds attached) by the wind in winter and early spring.

False Acacia does not have wide spreading limbs, but relatively short branches and aren’t prone to break of their own weight or during storms. However the tree as a whole may be susceptible to storms, as it does not have a taproot and the hard wood can be brittle. Otherwise it is a long-lived tree.
It can grow to 25 meters with a diameter of about 90 cm. There is a champion tree in Kew gardens that is 27 m high and has a diameter of 112 cm (measured in 2001)

Many varieties and cultivars of Black Locust has been bred during the several hundred years of cultivating this tree. These include both ornamental varieties, suitable as a street or garden tree and strains, which are more suitable for forestry. The huge worldwide interest in this tree will no doubt produce many more.
In the USA research is taking place to find strains which are resistant to borer insects, such as the locust stem borer, Megacyllene robinae, which does a lot of damage, because its larval tunnels makes the wood unusable and weaken the tree, which can then become very prone to wind damage. Heart rot (Fomes rimosus) can often follows borer attack, especially in older trees.
These pests are generally not present in other countries where the tree has been naturalised or planted.

Most natural reproduction of False Acacia/Black Locust is vegetative by means of root suckering and stump sprouting. Propagation is usually by seed or suckers.
Seed production can be variable. Trees will probably start to bear fruit from about 3-6 years onwards, although there have been incidences of a tree starting to fruit only at 60 years old. The best seed crop are found between 15 and 40 years old and years of heavy fruiting and then a much lighter crop are common. The fragrant flowers (10-25 cm long hanging racemes) appear in May and June soon after the leaves. In Britain the tree often fails to flower. Pollination is by insects, especially bees. 4 to 8 seeds grow in a pod and ripen in September/October. These pods open on the tree during the Winter and early Spring. Nevertheless there are very few seedlings. The seeds have hard, impermeable outer coats, which are relatively impervious to water. The seeds must therefore be softened by treatment with sulfuric acid, soaking in hot water, or scarification. Due to the hard coats the seeds stay viable for many years. A kilo will contain roughly 35,000-50,000 seeds.
(I had a batch of seeds one year, which I soaked in hot water and had reasonable germination. Once germinated, the seedlings were very easy to grow – webmother)
Early growth is very speedy and can be from 45 cm to 120cm a year, depending on the site.

Black locust can be vegetatively propagated from shoot and root cuttings, but success rates vary. Grafted or rooted shoot sections produce lateral growth, while sprouts from roots grow upright (Prentice 1987).
You can try hardwood cuttings (15-30 cm long and 1-2 cm diameter) collected in winter or early spring. Treatment with indole acetic acid improves rooting.

The tree likes well-drained soil and full sun, but will grow in almost any soil. However, it will not grow so well in competition with other trees, vines, or grasses, nor will it grow well on very poorly drained, heavy-textured soils. Nevertheless it has been said that it will tolerate soils that are to poor, compact or dry and hot for any other tree and therefore it has been recommended for use as a pioneer tree on coal tips and as a street tree
Fast grower: 40 feet in 20 years. Strong root system. Young trees has been used to contain embankments and hillsides. Resistant to pollution and dryness.

People have noticed, that if the roots are damaged for some reason, e.g. through ploughing or digging, the growth of root suckers will increase.
In the right conditions, it can spread fast via suckering and may become a pest.
Black locust is a legume. Nitrogen-fixing bacteria associated with nodules on the roots increase nitrogen content of the soil in which the tree grows.

The tree is said to be resistant to honey fungus.

The light to dark brown wood is beautiful, strong, hard and highly resistant to rot. I have heard reports of Locust fence posts in Virginia that have stood in the ground for at least 70 years, some say that posts have been able to functional for an amazing 100 years. A tree that produces such wood is of course a valuable asset. Think for example of vineyards, who need lots of stakes to hold up their valuable vines. Its is a lot of work to replace the vine supports, but using Robinia stakes one could rest assured in the knowledge that the vine supports takes will not need replacing for the next 50 years.
The wood has a specific gravity of 0.68 and has the lowest shrinkage value of the domestic woods produced in the USA.
It should be pointed out that the finest wood comes from the poorest soils, because the slower growth makes the wood denser and harder. Faster growth on fertile soils may produce wood that has larger cells and is relatively brittle. I could be that the disagreement between people who think this is a marvelous high-quality wood and those who think it is rather brittle, may be due to soil and growth factors.
In the USA it has been used as a substitute for teak and it is used in the making of a wide variety of products: paneling, siding, flooring, furniture, boat building, decking, vineyard or nursery props, fruit boxes, pallets, and so on. It makes good wood pulp for paper and board, good charcoal and a quality firewood (although it can sometimes flare up and/or spark).
“In the past it has also been used for agricultural implements, tool handles, shoe lasts, sports goods, dowels and pins for insulators on telephone and telegraph wires, tree nails (wooden pins used to fasten the planks to the ribs or timber of a ship), boat ribs, brackets, sleepers, and sills. It is used also for light construction, gates, wagon hubs, cart wheels, shipbuilding, furniture and turnery work. It is avoided for larger construction purposes, because although it may be hard, it can also be brittle and possibly lack ‘bounce’. Some burrs of the trees provide attractive wood for tabletops, and music cabinets.”
Some American farmers use to like to grow a few Robinia’s on the homestead to provide for home timber needs, and it appears that Hungarian farmers are continuing this practice. The tree has become one of Hungary’s most common forest trees. In 1991 nearly a fifth of its plantations consisted of Locust. One of the foremost varieties used is the “Shipmast Locust” originating from Long Island in New York State. This tree does not set seed freely and Hungarian forest researchers have perfected the art of raising large amounts of tall growing clones from tissue cultures.
Black Locust has one of the highest net photosynthetic rates among woody plants and its biomass potential is considerable. In Korea the tree is used in fuel-wood plantations. The tree can be coppiced or lopped annually for fuel.

CAUTION: Toxicity!
It is quite confusing to establish the exact danger posed by the toxicity of the Black Locust. The foliage has been used as animal fodder in places like the Himalayas and elsewhere. Some bits of the tree, such as seeds, young pods and flowers have been used as human food (Please see below).
Considering the marvelous decay resistance of the wood to the degree that it can act as a commercial wood preservative, it is obvious that the tree produces chemicals which are toxic to some forms of life. The question is what bits of the tree are toxic and which can be used for medicinal purposes or food?
Mrs. Grieve (1931) reports that “Occasional cases of poisoning are on record in which boys have chewed the bark and swallowed the juice: the principal symptoms being dryness of the throat, burning pain in the abdomen, dilation of the pupils, vertigo, and muscular twitches; excessive quantities causing also weak and irregular heart action.
The root and bark have been used for their emetic and purgative properties, but of course this is area that is unsuitable for self-medication, as only someone with experience would know what the difference is between a therapeutic dose and poisoning.
The leaves are used as fodder for the larger grazing animals, but seem to be toxic to insects.
Seeds, young pods and flowers are said to be edible when cooked by humans. Please remember that this website shares this information without being able to take responsibility for its accuracy. We like to hear from anyone who has experience with this tree and can give more information.
Other species too have these toxic and edible qualities sometimes. As I’m writing this it occurs to me that Elder flowers are like the Robinia flowers used in fritters and pancakes and that their leaves, like those of Robinia have insecticidal properties.


Erosion control and reforestation on difficult sites
Black Locusts make ideal trees for colonizing degraded sites due to its ability to cope with extremes such as drought, air pollutants, and high light intensities and its nitrogen fixing ability, fast growth and dense wood.
The trees have also been used for stabilising banks, because they have the habit of ‘suckering’ extensively. This means that the underground roots throw up shoots, which if allowed to do so, will grow into trees. Cutting the tree down will cause increased suckering.

Soil improver
Its nitrogen fixing ability makes Black Locusts a good candidate for companion planting schemes in agroforestry layouts. It can for example be intercropped (in a socalled “Alley system”) with vegetables. Strips of trees improve the micro-climate, reduce weather damage to the crops growing nearby and can also be harvested in their own right.
Experiments to mix Robinia with Conifers in forestry have not been very successful, because the Locust grow faster than the Conifers. The shading and over-topping led to a situation where the Conifers suffered a much reduced growth and were not thriving.

The dense growth habit of the tree has made it popular as a fast growing windbreak in some cases and it seems to be often used for this purpose in China.

Wood preservative?
“Black locust wood is being studied to find the chemical basis for its remarkable decay resistance. High flavonoid concentrations (6% of dry weight) are important, especially the constituents robinetin and dihydrorobinetin (Smith et al. 1989). When impregnated into easily decayed woods, heartwood extracts have raised decay resistance to a level equivalent to that attained by commercial wood preservatives (Smith et al. 1989).”
Resistance to rot may be due to the wood containing 4% taxifolin, an isomer of dihydroquercetin, or dihydrorobinetin, a growth-inhibitor of wood-destroying fungi. The flower is said to contain the antitumor compound benzoaldehyde. Some have classified the honey as toxic, others as the best of honeys (Shah, 1972).

The Plants For A Future (PFAF) database gives the following information:
A drying oil is obtained from the seed.
An essential oil is obtained from the flowers. Highly valued, it is used in perfumery

A yellow dye is obtained from the bark
“Robinetin is a strong dyestuff yielding with different mordants different shades similar to those obtained with fisetin, quercetin, and myricetin; with aluminum mordant, it dyes cotton to a brown-orange shade”(C.S.I.R., 1948–1976).

The bark contains tannin, but not in any huge quantities and probably not in sufficient quantity for utilization. On a 10% moisture basis, the bark contains 7.2% tannin and the heartwood of young trees 5.7%.

The bark has been used to make paper and can be used as a substitute for silk and wool.
Because of the fast growth of the tree, it has great potential as biomass and thus also as a source of paper pulp.

Natural insecticide?
The leaves are said to be insecticidal. However I do not know in what form and would like to hear from anyone with more information. I have read that he bruised foliage mixed with sugar will attract and kill flies. Would love to hear from anyone who has tried this to see how well it works?
Another possibility could be that a strong brew is made from the leaves and used for spraying?
It is interesting in this context that the leaf juice is also known to inhibit viruses.

Honey Producer
Bees love the flowers! In areas where the tree flowers freely, it is highly esteemed for the quality of the honey that the bees produce from it and some say this is the worlds finest honey. The Robinia honey from the Danube basin is known as Acacia honey and commands a higher price than any other honey. Research to develop varieties which flower later and have high nectar sugar content has been taking place in Hungary and the USA.

Fodder tree
Black Locust can be used a fodder tree and appears to be important for this use in the Himalayas, where the tree has naturalised. It is also used for this purpose in Korea and Bulgaria.
With the input of human energy a very efficient use of sparse land resources can potentially be achieved, especially for subsistence farmers. A tree is capable of producing far more greenery in a given spot, than this same amount of land would have produced as conventional grazing, even if only a quarter of its leaves would be eaten. Branches out of reach of life stock are cut whenever required and the remaining wood is used as fuel.
Ground black locust tops including woody stems have a good crude protein content of 23-24% and 7% lignin, and 4.2 kcal/g. Ruminal digestion by cattle was also equivalent (Baertsche et al. 1986)
There may be some problems with the tannins and lectin proteins found in leaves and inner bark, because they can interfere with digestion in ruminants and in nonruminants. To much tannin has the effect of “leatherising” the mucous coating of the digestive tract by coagulating the protein found in the mucous. (It is of course for this that tannins have been used to create durable leather from animal skins). In the alimentary canal this have the effect that nutrients do not absorbed into the bloodstream of the gut, but simply pass out the other end.
Since tannin levels are high in young leaves but decrease as leaves mature, it is therefore advisable to lop only the more mature leaves as fodder.
The high nutritional value of the leaves (similar to alfalfa (Medicago sativa L.) makes it feasible to consider commercial feed production, as silage, hay or leaf meal.
The tree has probably developed its thorns to protect itself from browsing animals. No doubt people will try to find varieties which are thornless. There have been trials in the USA to grow this plant as a conventional foddercrop at planting densities from 40,000 to 1,000,000 per hectare. Conventional hay-cutting equipment was used for harvesting and it was noticed that the stipular thorns on new growth do not become sharp until the stem turns woody

Human Food (Please read Caution)
The seeds, young pods and flowers are edible when cooked. The seeds are said to lose their acid taste after boiling.
The creamy white flower racemes have been used to make delicious fritters. Similarly they can be added to pancakes. Other uses of the flowers are as an addition to jam or for making a pleasant tea.
The PFAF database mentions that Piperonal is extracted from the plant, and that it is used as a vanilla substitute. Alas there is no more information available to me than these bare facts, but I wonder if the piperonal is extracted from the flowers, as they have a lovely vanilla aroma. Therefore the piperonal may be the name for an essential oil from the flowers that has reportedly been used as a spice, in sherberts and toilet waters.
I have read that a strong, narcotic and intoxicating drink is made from the skin of the fruit, but I have no details about doses and effect.
Another reported usage that definitely requires further credentials is that Robinia can serve as a vegetable rennet. The only additional information I can give is a statement from Mrs. Grieve’s Modern Herbal, which says that: “The inner bark contains a poisonous proteid substance, Robin, which possesses strong emetic and purgative properties. It is capable of coagulating the casein of milk and of clotting the red corpuscles of certain animals.”
I certainly would not recommend this use unless more information becomes available.

Medicinal (Please read Caution)
The living tradition of the medicinal use of this tree has largely been lost, or at least I have not found examples of contemporary use. All the same, Black Locust is reported to have a long catalogue of medicinal qualities, which I have listed below with an explanation of the term.

– Anti-spasmodic – Helps to relieve muscular spasms and cramps.
– Anti-viral – Helps the body fight viral diseases
– Astringent – Tightens and tones bodily tissues and reduces the flow of secretions and discharges of blood, mucus, diarrhoea etc. Cholagogue – Increases the flow of bile and its discharge from the body, which often also has as it result a slight improvement of liver function and digestion. Diuretic – Promotes the flow of urine.
– Aromatic – Has an agreeable odour and stimulant qualities.
– Emetic – Induces vomiting (a useful ‘therapy’ in a few circumstances).
– Emollient – Softens (e.g. the skin) and soothes inflamed or irritated surfaces (internally and externally).
– Febrifuge – Reduces fevers.
– Laxative – Relieves constipation and stimulates bowel movements in a fairly gentle manner.
– Narcotic – In therapeutic doses induces drowsiness, reduces sensibility, relieves pain, induces sleep and gives an artificial sense of well-being. In larger doses it causes stupor, coma and convulsions.
– POISON – See above.
– Protisticidal – kills a group of organisms which includes the unicellular plants and animals and, on some classifications, the viruses.
– Purgative – Relieves constipation and stimulates bowel movements in a fairly drastic manner.
– Sedative – Gently calms, reducing nervousness, distress and irritation.
– Tonic – Improves the tone of a body organ and/or the general condition of a patient and so improves general health. Slower acting than a stimulant, it brings steady improvement.

The following are the main remnants of knowledge left to us that give us some insight in how the above properties for pseudoacacia were used in practice (sourced mostly from the PFAF database)

– Cherokee used the plant as an emetic and for toothache
– Black locust has been a folk remedy for dyspepsia and spasms in the USA (Duke and Wain, 1981)
– The flowers are antispasmodic, aromatic, diuretic, emollient and laxative
– The flowers are cooked and eaten for the treatment of eye ailments
– The inner bark and the root bark are emetic, purgative and tonic
– The root bark has been chewed to induce vomiting
– The root bark has been held in the mouth to allay toothache
– The leaves are cholagogue and emetic
– The leaf juice inhibits viruses
– A tea made from the flowers was tried for headaches, stomach pains, and nausea
– black locust blossoms steeped in wine were used to treat anemia.

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