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The ailanto (ailanthus altissima), also known with the popular names of "tree of paradise" and "false Sommaco", is a tree belonging to the Simaroubaceae family, formed by about 20 genera and about 150 species of trees and shrubs coming both from from the tropical and subtropical regions, and from the temperate regions of Asia.
The ailanthus is the most well-known and widespread exponent of this family, especially in Europe and the American continent.
Genus that has about ten species of trees, up to 25-30 meters tall, originating from Asia and northern Australia, very common in Europe and the United States. They have erect stems and very branched foliage; the bark is light brown, gray on the branches; the leaves are composed, consisting of 15-20 small oval leaves, bright green, alternate, an entire leaf can be even 40-50 cm long. In late spring the female trees produce small bunches of yellow-green flowers, followed by numerous small paper samaras at the end of the summer, which remain on the tree for many months. This plant, in some areas of the globe, is considered a weed and therefore in these places it is not advisable to place it in the garden. The leaves, flowers and bark give off an unpleasant smell; in some cases it seems that the ailanthus secrete a toxin that prevents the engraftment of other trees in the vicinity. Before laying a home ailanthus It is good to know that it produces a conspicuous and very deep root system.
These trees grow in any position, preferring open and bright spaces; they were widely used for street trees, as they bear pollution very well. Likewise, they tolerate cold, drought, summer heat and strong winds.Ailanthus roots
The hypogeum apparatus is very developed (and this is why eradication is extremely difficult). It is composed of large rhizomes and can spread vigorously even horizontally, thanks to the ability to emit large numbers of suckers.
They are deciduous, imparipinnate, up to 60 cm long, with more than 15 pairs of leaflets, up to 12 cm long and 5 wide. They have entire margins and, near the base, are characterized by a deep incision. As soon as they come to light they are a very bright purple red, then turn to dark green. They give off a smell that is most unpleasant.
They are greenish-yellow in color, sometimes with reddish shades, composed of 5-6 petals. They are produced in large panicles (even 20 cm long) at the apex of the branches. Generally it is a dioecious plant: this means that there are individuals that produce only male inflorescences and others only feminine. In any case, there are also specimens with hermaphrodite flowers and therefore capable of self-fertilizing.
The corollas are produced from the middle to the end of the summer. The male flowers give off an unpleasant smell (similar to that of the leaves), while the feminine ones are mostly free (and for this the specimens of this sex were preferred for ornamental purposes).
Fruits and seeds
The fruits are winged, up to 4 cm long, collected in groups of up to 4. Maturing they pass from a greenish color to red-brown.
The seeds of ailanthus have a good germination ability, and can also be sown as dwelling, although it is advisable to prepare small plants in a container, with fertile and well-drained soil, rich in sand; the plants develop numerous basal suckers, which can be removed and rooted in a mixture of sand and peat in equal parts. Ailanthus can also be propagated by branch or root cutting.
Pests and diseases
These trees are not affected by pests or diseases.
This species is native to the southern regions of China, where it has been known since very ancient times. It was introduced in Europe in the 18th century by the Jesuit father Pierre d'Incarville who was responsible for sending a good quantity of seeds. In the middle of the century, some French botanists began to sow them and to share them with other European scholars, especially English. They had more luck in germination and sent specimens to Paris at the end of the 1700s. From that moment this tree was considered ornamental and began to spread throughout the continent, with extreme ease. In 1784 it was also introduced in the United States.
After an initial period of confusion with other essences, it was finally classified as belonging to a genus of its own, the specially created Ailanthus: it literally means "tree of paradise". The name of the species, very high, refers to the comparison with the tree of the lacquer, Toxicodendron vernicifluum, which is more modest in size.
Relations with the silk industry
Its diffusion was further favored by the idea of using it as a substitute for mulberry for silk production.
Many specimens were planted in the regions where this industry was developed: all of France and Northern Italy (in particular Piedmont and Lombardy). Consequently a parasite was also introduced: the Philosamia cynthia. It is a butterfly that, like the silkworm, forms a cocoon from which the precious filament can be made. It is a much larger moth and which could guarantee higher production (even if of lower quality).
The experiment, however, turned out to be a total failure as the caterpillars were easy prey for the birds and never managed to reproduce and colonize the plantations in sufficient numbers to justify the massive cultivation.
The wave of plants was thus interrupted and the commercialization continued only for ornamental uses.
Which species could be confused with?
It could be confused with the greater sumac (Rhus typhina), another intrusive exotic plant. They can be distinguished by observing the flowers, which in this case are greenish, and the toothed leaves. Furthermore, the Rhus rarely exceeds 8 meters in height.
It could also be confused with fraxinus excelsior, a major ash. The latter, however, has black buds and the leaves are composed of a maximum of 12 leaflets.
This tree is frequently found on fairly dry soils, from sea level up to a maximum of 1000 meters, mostly in a hilly environment. In any case, the environment in which it finds the maximum development and in which its diffusion becomes almost uncontrollable is characterized by soils rich in nitrogen and with pH from neutral to subacid.
It is consequently very frequent both in the areas surrounding the woods, in the meadows or, even more, where the environment is strongly manipulated by man (for example industrial areas, roadsides, agricultural land left uncultivated).
The amount of water present in the soil is irrelevant: it can in fact be called a xerophilous plant, given its ability to limit evaporation by closing the stomata present on the leaves.
The root system also supports this characteristic. In fact the seeds are already able from the early stages of development to introduce a taprooting root into the soil up to large depths. The plant, in this way, is immediately very resistant to drought, withstanding temperatures even above 40 ° C for prolonged periods.
Moreover, it is considered to all intents and purposes a pioneer plant. It manages to creep into a territory taking advantage of natural disasters (such as storms, fires, defoliators). On the other hand, it is very difficult to expand when it competes with dense forests and wooded areas.
Temperatures and adaptability
The ailantus tends to like mild to hot temperatures. When it was introduced, in fact, it was rather sensitive to cold. It was immediately noticed, however, that once the juvenile stage had been passed, the individuals were able to withstand even very harsh winters (up to -30 ° C). They are not even disturbed by the salinity present in the soil or possibly in the air.
They are growing more and more vigorously in urban areas because for them it is not a problem even a high rate of pollution.
In recent studies, on the other hand, a marked sensitivity to high ozone levels has been noted. We then started monitoring them to see if they could be useful in this respect.
Why does this plant become so invasive?
The establishment of an ailanthus population is based on a double reproduction strategy.
First of all a single tree is capable of producing seeds already from very young and very copiously (up to 300000). Thanks to their shape, moreover, they are able to reach very far (up to 70 meters), even with a very weak wind. The seeds are then released all in the same period: dissemination occurs in stages starting from November until May. In this way the possibilities to find ideal conditions for gemination increase exponentially.
Secondly, young individuals quickly establish themselves thanks to the tap-root, where starch accumulates. Later a more superficial hypogeum develops which can be enlarged up to a diameter of 45 meters. From this will surely be produced of suckers that will continue, producing over time an autonomous radical system, the work of colonization.
The ailanto is therefore an exceptionally fast growing species: up to an area of 4 square meters per year.
Uses of the ailanto
Its wood is a good fuel that produces flames of light color and leaves few ashes.
Young trees can be used by the paper industry or, due to its workability, for the production of small objects.
In China it is widely used in traditional medicine, in particular the bark, fruits and roots are considered useful for the treatment of nervous and bowel diseases.
Its flowers particularly attract bees and its nectar becomes part of millefiori honeys.
Scholars have isolated the ailanthin alkaloid that could be used in the treatment of various diseases. Some extracts may also be useful as insecticides and herbicides.
Ailanto: How to avoid spreading the ailanto?
Throughout Italy this plant is considered invasive. It is therefore absolutely not recommended to place it in the gardens and indeed, it would be necessary to intervene to limit its diffusion as much as possible.
First of all, small plants must be eliminated immediately and totally eradicated.
Secondly, it is absolutely essential to remove the cobs containing the seeds as soon as possible, preventing them from maturing.
In addition to this, it is possible to proceed with regular cuts of the suckers so that they are discouraged from being pushed back.
Other possible interventions are the administration of herbicides and possibly the trimming of the trunks, which leads to the final death of the subject.
The trees of paradise
The Ailanto, better known as the tree of paradise, includes about ten species that reach maximum heights of about 2
visit: the trees of paradise