Reproduction of Black locust
Reproduction of Black locust
Black locust (Robinia pseudoacacia L.) is a tree of the Fabaceae family, native to North America and subsequently largely naturalized in Europe and other continents.
Suitable breeding habitat –
Robinia pseudoacacia is a plant native to North America, with particular reference to the Appalachian area, where it is found in pure woodland formations.
In its range of origin it is widespread in eastern North America, on the Appalachian and Ozark mountain ranges in Pennsylvania, West Virginia, Kentucky, Georgia, Illinois, Missouri and Oklahoma.
Its natural habitat is that of the woods where, as mentioned, it can be found in pure formations especially in deep and well-drained calcareous soils.
From its range it was then introduced to other countries such as Europe, from where it has been present for more than four hundred years.
It was imported from North America in 1601 by Jean Robin, pharmacist and botanist of the French king Henry IV. The introduction was through seeds from the Appalachian Virginia, delivered to Robin by the English botanist John Tradescant the Elder.
After arriving in the old continent it spread spontaneously in the most disparate environments where it is now naturalized in most of central Europe, from southern England and Sweden, up to Greece, Spain and Cyprus. It is particularly widespread in France, Germany, the Netherlands, Belgium, Luxembourg, Switzerland, Austria, Hungary, Italy, Slovenia. It is also naturalized in Türkiye and Israel as well as Australia and New Zealand. It is also widely cultivated in wood plantations in various European (Hungary: 270,000 hectares; France: 100,000 hectares) and non-European countries (China: 1 million hectares; South Korea: 270,000 hectares). It is also widespread in Africa.
In Italy the black locust was introduced in 1662 in the Botanical Garden of Padua.
Now this plant is present practically everywhere, in particular in Piedmont (where pure and mixed locust woods cover an area of about 85,000 hectares), in Lombardy, in Veneto and in Tuscany (where there are very productive coppices).
In Italy it is present from sea level up to about 1000 m in the central north and up to 1600 m in the south.
Propagation –
Robinia pseudoacacia is a plant of the temperate zone, where it is found at altitudes of up to 3,300 metres. It grows best in areas where annual daytime temperatures are between 15-32°C, but can tolerate 6-40°C.
In a dormant state it can survive temperatures down to about -35°C, but the shoots can be severely damaged at -1°C.
It prefers an average annual rainfall between 450 and 700 mm, but tolerates between 300 and 1,600 mm.
It is a very tolerant plant, it grows best in full sun but tolerates some shade and, moreover, it grows in any well-drained soil, preferring one that is not too organic.
It is tolerant to soil salinity and atmospheric pollution.
From a soil point of view, it prefers a pH between 5.5 and 6.5, tolerating between 4.5 and 8.2.
It is a fast growing tree for the first 30 years of its life and can start flowering and producing seeds when it is only 6 years old, although it is fully grown at 10 – 12 years old.
This species has a symbiotic relationship with some soil bacteria; these bacteria form nodules on the roots and fix atmospheric nitrogen.
Propagation is by seed. We recommend pre-soaking it for 48 hours in warm water and sowing it at the end of winter in a protected area or unheated greenhouse.
Short layering improves germination speed and time.
The young seedlings are then placed in single pots as soon as they are manageable. The transplant must be carried out in the following summer or, in milder climates, also in spring.
The seed can be kept for over 10 years and it has been verified that some seeds have remained viable in the soil for more than 88 years.
Ecology –
Carlo Linnaeus, the great naturalist to whom we owe the scientific names of thousands of plants, named the species Robinia pseudoacacia, establishing the genus Robinia, whose name was coined to recall that of Jean Robin, who had introduced the tree in Europe.
Robinia pseudoacacia is an important melliferous plant: acacia honey is obtained from it.
Like all legumes, it is in root symbiosis with nitrogen-fixing microorganisms and therefore enriches the soil with nitrogen, an important nutrient element. Overall, the black locust is a pioneer species, which has a limited longevity outside its natural vegetation area (60-70 years) and therefore in the most fertile areas it is a transitory species which can be gradually replaced by other more long-lived species.
The more than three centuries of presence in Italy have in fact included this species in various ecological cycles, as its diffusion is limited by: Eulecanium corni; Cossus cossus, Parectopa robiniella and Phiylonorycter, which are leaf miners in the larval stage; Aphis craccivora, aphid found in its leaves and shoots; Armillaria mellea, Obolodiplosis robiniae, appeared in 2003 in Veneto, cecidomide diptera specific parasite of locust tree; in 2004 this species also spread to the Po Valley.
In some environments, especially those degraded by man, this plant behaves as an invasive species; it has a high growth speed, especially if coppice: the suckers, which emerge both from the stump and from its extensive root system, grow rapidly; for this reason it often competes successfully with slower growing native species. Furthermore, its extreme adaptability makes it at ease from the coasts to the 1000 meters of altitude of the shady submontane valleys. The consequence is the formation of woods with a reduced variety of tree species, fewer specimens of autochthonous tree species and a scarcity of nemoral flora and fungi; in Italy the problem is present above all in the Po Valley and in the pre-Alpine and Apennine valleys. Of course, locust trees used as ornamentals in urban centers pose no problem.