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tree-of-heaven

Ailanthus altissima

Summary 4

Ailanthus altissima /eɪˈlænθəs ælˈtɪsɪmə/, commonly known as tree of heaven, ailanthus, or in Standard Chinese as chouchun (Chinese: 臭椿; pinyin: chòuchūn; literally: "foul smelling tree"), is a deciduous tree in the Simaroubaceae family. It is native to both northeast and central China, as well as Taiwan. Unlike other members of the genus Ailanthus, it is found in temperate climates rather than the tropics. The tree grows rapidly and is capa

As an exotic plant 5

The earliest introductions of A. altissima to countries outside of its native range were to the southern areas of Korea as well as to Japan. It is possible that the tree is native to these areas, but it is generally agreed that the tree was a very early introduction. Within China itself it has also been naturalized beyond its native range in areas such as Qinghai, Ningxia and Xinjiang.

In 1784, not long after Jussieu had sent seeds to England, some were forwarded to the United States by William Hamilton, a gardener in Philadelphia. In both Europe and America it quickly became a favoured ornamental, especially as a street tree, and by 1840 it was available in most nurseries. The tree was separately brought to California in the 1890s by Chinese immigrants who came during the California Gold Rush. It has escaped cultivation in all areas where it was introduced, but most extensively in the United States. It has naturalized across much of Europe, including Germany, Austria, Switzerland, the Czech Republic, the Pannonian region (i.e. southeastern Central Europe around the Danube river basin from Austria, Slovakia and Hungary south to the Balkan ranges) and most countries of the Mediterranean Basin. In Montenegro and AlbaniaA. altissima is widespread in both rural and urban areas and while in the first it was introduced as an ornamental plant, it very soon invaded native ecosystems with disastrous results and became an invasive species. Ailanthus has also been introduced to Argentina, Australia (where it is a declared weed in New South Wales and Victoria), New Zealand (where it is listed under the National Pest Plant Accord and is classed an "unwanted organism"), the Middle East and in some countries in South Asia such as Pakistan. In South Africa it is listed as an invasive species which must be controlled, or removed and destroyed.

In North America, A. altissima is present from Massachusetts in the east, west to southern Ontario, southwest to Iowa, south to Texas, and east to the north of Florida. On the west coast it is found from New Mexico west to California and north to Washington. In the east of its range it grows most extensively in disturbed areas of cities, where it was long ago present as a planted street tree. It also grows along roads and railways. For example, a 2003 study in North Carolina found the tree of heaven was present on 1.7% of all highway and railroad edges in the state and had been expanding its range at the rate of 4.76% counties per year. Similarly, another study conducted in southwestern Virginia determined that the tree of heaven is thriving along approximately 30% of the state's interstate highway system length or mileage. It sometimes enters undisturbed areas as well and competes with native plants. In western North America it is most common in mountainous areas around old dwellings and abandoned mining operations. It is classified as a noxious or invasive plant on National Forest System lands and in many states because its prolific seed production, high germination rates and capacity to regrow from roots and root fragments enable A. altissima to out-compete native species. For this reason, control measures on public lands and private property are advised where A. altissima has naturalized.

Description 5

A. altissima is a medium-sized tree that reaches heights between 17 and 27 metres (56 and 89 ft) with a diameter at breast height of about 1 m (40 inches). The bark is smooth and light grey, often becoming somewhat rougher with light tan fissures as the tree ages. The twigs are stout, smooth to lightly pubescent, and reddish or chestnut in color. They have lenticels as well as heart-shaped leaf scars (i.e. a scar left on the twig after a leaf falls) with many bundle scars (i.e. small marks where the veins of the leaf once connected to the tree) around the edges. The buds are finely pubescent, dome shaped, and partially hidden behind the petiole, though they are completely visible in the dormant season at the sinuses of the leaf scars. The branches are light to dark gray in color, smooth, lustrous, and containing raised lenticels that become fissures with age. The ends of the branches become pendulous. All parts of the plant have a distinguishing strong odor that is often likened to peanuts, cashews, or rotting cashews.

The leaves are large, odd- or even-pinnately compound, and arranged alternately on the stem. They range in size from 30 to 90 cm (1 to 3 feet) in length and contain 10–41 leaflets organised in pairs, with the largest leaves found on vigorous young sprouts. When they emerge in the spring, the leaves are bronze then quickly turn from medium to dark green as they grow. The rachis is light to reddish-green with a swollen base. The leaflets are ovate-lanceolate with entire margins, somewhat asymmetric and occasionally not directly opposite to each other. Each leaflet is 5–18 cm (2-7 inches) long and 2.5–5 cm (1-2 inches) wide. They have a long tapering end while the bases have two to four teeth, each containing one or more glands at the tip. The leaflets' upper sides are dark green in color with light green veins, while the undersides are a more whitish green. The petioles are 5–12 mm (0.2-0.5 inch) long. The lobed bases and glands distinguish it from similar sumac species.

The flowers are small and appear in large panicles up to 50 cm (20 in) in length at the end of new shoots. The individual flowers are yellowish green to reddish in color, each with five petals and sepals. The sepals are cup-shaped, lobed and united while the petals are valvate (i.e. they meet at the edges without overlapping), white and hairy towards the inside. They appear from mid-April in the south of its range to July in the north. A. altissima is dioecious, with male and female flowers being borne on different individuals. Male trees produce three to four times as many flowers as the females, making the male flowers more conspicuous. Furthermore, the male plants emit a foul-smelling odor while flowering to attract pollinating insects. Female flowers contain ten (or rarely five through abortion) sterile stamens (stamenoides) with heart-shaped anthers. The pistil is made up of five free carpels (i.e. they are not fused), each containing a single ovule. Their styles are united and slender with star-shaped stigmas. The male flowers are similar in appearance, but they of course lack a pistil and the stamens do function, each being topped with a globular anther and a glandular green disc. The fruits grow in clusters; a fruit cluster may contain hundreds of seeds. The seeds borne on the female trees are 5 mm in diameter and each is encapsulated in a samara that is 2.5 cm (0.98 in) long and 1 cm (0.39 in) broad, appearing July though August, but can persist on the tree until the next spring. The samara is large and twisted at the tips, making it spin as it falls, assisting wind dispersal, and aiding buoyancy for long-distance dispersal through hydrochory. Primary wind dispersal and secondary water dispersal are usually positively correlated in A. altissima since most morphological characteristics of samaras affect both dispersal modes in the same way – except for the width of the samaras, which in contrast affects both types of dispersal in opposing ways, allowing differentiation in the dispersal strategies of this tree. The females can produce huge amounts of seeds, normally around 30,000 per kilogram (14,000/lb) of tree, and fecundity can be estimated non-destructively through measurements of dbh.

Distribution and habitat 5

A. altissima is native to northern and central China, Taiwan and northern Korea. It was historically widely distributed, and the fossil record indicates clearly that it was present in North America as recently as the middle Miocene. In Taiwan it is present as var. takanai. In China it is native to every province except Gansu, Heilongjiang, Hainan, Jilin, Ningxia, Qinghai, Xinjiang, and Tibet. It has been introduced in many regions across the world.

The tree prefers moist and loamy soils, but is adaptable to a very wide range of soil conditions and pH values. It is drought-hardy, but not tolerant of flooding. It also does not tolerate deep shade. In China it is often found in limestone-rich areas. The tree of heaven is found within a wide range of climatic conditions. In its native range it is found at high altitudes in Taiwan as well as lower ones in mainland China. These are virtually found anywhere in the U.S., but especially in arid regions bordering the Great Plains, very wet regions in the southern Appalachians, cold areas of the lower Rocky Mountains and throughout much of the California Central Valley, forming dense thickets that displace native plants. Prolonged cold and snow cover cause dieback, although the trees resprout from the roots.

The earliest introductions of A. altissima to countries outside of its native range were to the southern areas of Korea as well as to Japan. It is possible that the tree is native to these areas, but it is generally agreed that the tree was a very early introduction. Within China itself it has also been naturalized beyond its native range in areas such as Qinghai, Ningxia and Xinjiang.

In 1784, not long after Jussieu had sent seeds to England, some were forwarded to the United States by William Hamilton, a gardener in Philadelphia. In both Europe and America it quickly became a favoured ornamental, especially as a street tree, and by 1840 it was available in most nurseries. The tree was separately brought to California in the 1890s by Chinese immigrants who came during the California Gold Rush. It has escaped cultivation in all areas where it was introduced, but most extensively in the United States. It has naturalized across much of Europe, including Germany, Austria, Switzerland, the Czech Republic, the Pannonian region (i.e. southeastern Central Europe around the Danube river basin from Austria, Slovakia and Hungary south to the Balkan ranges) and most countries of the Mediterranean Basin. In Montenegro and AlbaniaA. altissima is widespread in both rural and urban areas and while in the first it was introduced as an ornamental plant, it very soon invaded native ecosystems with disastrous results and became an invasive species. Ailanthus has also been introduced to Argentina, Australia (where it is a declared weed in New South Wales and Victoria), New Zealand (where it is listed under the National Pest Plant Accord and is classed an "unwanted organism"), the Middle East and in some countries in South Asia such as Pakistan. In South Africa it is listed as an invasive species which must be controlled, or removed and destroyed.

In North America, A. altissima is present from Massachusetts in the east, west to southern Ontario, southwest to Iowa, south to Texas, and east to the north of Florida. On the west coast it is found from New Mexico west to California and north to Washington. In the east of its range it grows most extensively in disturbed areas of cities, where it was long ago present as a planted street tree. It also grows along roads and railways. For example, a 2003 study in North Carolina found the tree of heaven was present on 1.7% of all highway and railroad edges in the state and had been expanding its range at the rate of 4.76% counties per year. Similarly, another study conducted in southwestern Virginia determined that the tree of heaven is thriving along approximately 30% of the state's interstate highway system length or mileage. It sometimes enters undisturbed areas as well and competes with native plants. In western North America it is most common in mountainous areas around old dwellings and abandoned mining operations. It is classified as a noxious or invasive plant on National Forest System lands and in many states because its prolific seed production, high germination rates and capacity to regrow from roots and root fragments enable A. altissima to out-compete native species. For this reason, control measures on public lands and private property are advised where A. altissima has naturalized.

Ecology 5

Tree of heaven is an opportunistic plant that thrives in full sun and disturbed areas. It spreads aggressively both by seeds and vegetatively by root sprouts, re-sprouting rapidly after being cut. It is considered a shade-intolerant tree and cannot compete in low-light situations, though it is sometimes found competing with hardwoods, but such competition rather indicates it was present at the time the stand was established. On the other hand, a study in an old-growth hemlock-hardwood forest in New York found that Ailanthus was capable of competing successfully with native trees in canopy gaps where only 2 to 15% of full sun was available. The same study characterised the tree as using a "gap-obligate" strategy in order to reach the forest canopy, meaning it grows rapidly during a very short period rather than growing slowly over a long period. It is a short lived tree in any location and rarely lives more than 50 years. Ailanthus is among the most pollution-tolerant of tree species, including sulfur dioxide, which it absorbs in its leaves. It can withstand cement dust and fumes from coal tar operations, as well as resist ozone exposure relatively well. Furthermore, high concentrations of mercury have been found built up in tissues of the plant.

Ailanthus has been used to re-vegetate areas where acid mine drainage has occurred and it has been shown to tolerate pH levels as low as 4.1 (approximately that of tomato juice). It can withstand very low phosphorus levels and high salinity levels. The drought-tolerance of the tree is strong due to its ability to effectively store water in its root system. It is frequently found in areas where few trees can survive. The roots are also aggressive enough to cause damage to subterranean sewers and pipes. Along highways, it often forms dense thickets in which few other tree species are present, largely due to the toxins it produces to prevent competition. The roots are poisonous to people.

Ailanthus produces an allelopathic chemical called ailanthone, which inhibits the growth of other plants. The inhibitors are strongest in the bark and roots, but are also present in the leaves, wood and seeds of the plant. One study showed that a crude extract of the root bark inhibited 50% of a sample of garden cress (Lepidium sativum) seeds from germinating. The same study tested the extract as an herbicide on garden cress, redroot pigweed (Amaranthus retroflexus), velvetleaf (Abutilon theophrasti), yellow bristlegrass (Setaria pumila), barnyard grass (Echinochloa crusgalli), pea (Pisum sativum cv. Sugar Snap) and maize (Zea mayscv. Silver Queen). It proved able to kill nearly 100% of seedlings with the exception of velvetleaf, which showed some resistance. Another experiment showed a water extract of the chemical was either lethal or highly damaging to 11 North American hardwoods and 34 conifers, with the white ash (Fraxinus americana) being the only plant not adversely affected. The chemical does not, however, affect the tree of heaven's own seedlings, indicating that A. altissima has a defence mechanism to prevent autotoxicity. Resistance in various plant species has been shown to increase with exposure. Populations without prior exposure to the chemicals are most susceptible to them. Seeds produced from exposed plants have also been shown to be more resistant than their unexposed counterparts.

The tree of heaven is a very rapidly growing tree, possibly the fastest growing tree in North America. Growth of one to two metres (3.5-6.5 ft) per year for the first four years is considered normal. Shade considerably hampers growth rates. Older trees, while growing much slower, still do so faster than other trees. Studies found that Californian trees grew faster than their East Coast counterparts, and American trees in general grew faster than Chinese ones.

In northern Europe the tree of heaven was not considered naturalised in cities until after the Second World War. This has been attributed to the tree's ability to colonize areas of rubble of destroyed buildings where most other plants would not grow. In addition, the warmer microclimate in cities offers a more suitable habitat than the surrounding rural areas (it is thought that the tree requires a mean annual temperature of 8 degrees Celsius to grow well, which limits its spread in more northern and higher altitude areas). For example, one study in Germany found the tree of heaven growing in 92% of densely populated areas of Berlin, 25% of its suburbs and only 3% of areas outside the city altogether. In other areas of Europe this is not the case as climates are mild enough for the tree to flourish. It has colonized natural areas in Hungary, for example, and is considered a threat to biodiversity at that country's Aggtelek National Park.

Several species of Lepidoptera utilise the leaves of ailanthus as food, including the Indian moon moth (Actias selene) and the common grass yellow (Eurema hecabe). In North America the tree is the host plant for the ailanthus webworm (Atteva aurea), though this ermine moth is native to Central and South America and originally used other members of the mostly tropical Simaroubaceae as its hosts. In its native range A. altissima is associated with at least 32 species of arthropods and 13 species of fungi.

In North America, the leaves of ailanthus are sometimes attacked by Aculops ailanthii, a mite in the family Eriophyidae. Leaves infested by the mite begin to curl and become glossy, reducing their ability to function. Therefore, this species has been proposed as a possible biocontrol for ailanthus in the Americas.

Due to the tree of heaven's weedy habit, landowners and other organisations often resort to various methods of control in order to keep its populations in check. For example, the city of Basel in Switzerland has an eradication program for the tree. It can be very difficult to eradicate, however. Means of eradication can be physical, thermal, managerial, biological or chemical. A combination of several of these can be most effective, though they must of course be compatible. All have some positive and negative aspects, but the most effective regimen is generally a mixture of chemical and physical control. It involves the application of foliar or basal herbicides in order to kill existing trees, while either hand pulling or mowing seedlings in order to prevent new growth.


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Sources and Credits

  1. (c) Mattia Menchetti, some rights reserved (CC BY), uploaded by Mattia Menchetti
  2. (c) John Hilty, some rights reserved (CC BY-NC), http://www.illinoiswildflowers.info/trees/photos/tr_heaven1.jpg
  3. (c) Eric Rosenberg, some rights reserved (CC BY-NC), uploaded by Eric Rosenberg
  4. Adapted by Jeny Davis from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Ailanthus_altissima
  5. (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Ailanthus_altissima

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