Eucalyptus

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Eucalyptus
Eucalyptus melliodora foliage and flowers
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Myrtales Family: Myrtaceae Genus: Eucalyptus L'Hér.
Species
About 700; see the List of Eucalyptus species

Eucalyptus (From Greek, eu + καλύπτω = "True Cap") is a diverse genus of trees (and a few shrubs), the members of which dominate the tree flora of Australia. There are more than 700 species of Eucalyptus, mostly native to Australia, with a very small number found in adjacent parts of New Guinea and Indonesia and one as far north as the Philippines.

Eucalypts can be found in almost every part of the Australian continent, adapted to all of its climatic conditions; in fact, no other continent is so characterised by a single genus of tree as Australia is by eucalyptus. Many, but far from all, are known as gum trees, in reference to the habit of many eucalyptus to constantly exude sap from any break in the bark.

Contents 1 Description 1.1 Size and Habit 1.2 Flowers and leaves 1.3 Bark 1.4 Species & Hybridism 1.5 Related genera 1.6 Tall timber 1.7 Tolerance 2 Animal relationships 3 Hazards 4 Fire 5 Cultivation and uses 6 History 7 Plantation and ecological problems 7.1 California 7.2 Brazil 7.3 Ethiopia 8 References 9 External links 10 Photo gallery

[edit] Description

[edit] Size and Habit

A eucalypt may be mature as a low shrub or as a very large tree. There are three main habit and four size categories that species can be divided into.

As a generalisation, "forest trees" are single-stemmed and have a crown forming a minor proportion of the whole tree height, with the combined forest crowns occupying at least 30% of the ground cover. "Woodland trees" are single-stemmed although they may branch at a short distance above ground level, and have a crown occupying less than 30% of the the ground cover.

"Mallees" are multi-stemmed from ground level, usually less than 10 metres in height, often with the crown predominantly at the ends of the branchlets, and individual plants may combine to form either an open or closed formation. Many mallee trees may be so low growing as to be considered a shrub.

Apart from the forest tree, woodland tree, mallee and shrub habits, two further tree forms are notable in Western Australia. One of these is the "Mallet", which is a small to medium-sized tree, usually of steep branching habit, sometimes fluted at the base of the trunk, and often with a conspicuously dense, terminal crown. It is the habit usually of mature healthy specimens of Eucalyptus occidentalis, E. astringens, E. spathulata, E. gardneri, E. dielsii, E. forrestiana, E. salubris, E. clivicola and E. ornata. The smooth bark of mallets often has a satiny sheen and may be white, cream, grey, green or copper.

Another habit category used in Western Australia is the "Marlock". This has been variously applied but Brooker & Hopper (2001) defined the term and restricted the use to describe the more or less pure stands of short, erect, thin-stemmed "trees" that do not produce lignotubers. These are easily seen and recognised in stands of E. platypus, E. vesiculosa and the unrealted E. stoatei. The marlock is distinguished from mallets which are taller and have a characteristic steep branching habit. The origin and use of the term "morrel" is somewhat obscure and appears to apply to trees of the western Australian wheatbelt and goldfields, which have a long, straight trunk, completely rough barked. It is now used mainly for E. longicornis (Red Morell) and E. melanoxylon (Black Morrel).

Tree sizes follow the convention of:

• Small - to 10 metres in height
• Medium sized - 10 to 30 metres in height
• Tall - 30 to 60 metres in height
• Very Tall - over 60 metres in height

[edit] Flowers and leaves

The most readily recognisable characteristics of Eucalyptus species are the distinctive flowers and fruits. The name Eucalyptus, from the Greek words eu-, well, and kaluptos, cover, meaning "well-covered", describes the bud cap (botanically called an operculum). This cap forms from modified petals and falls off as the flower opens. Thus flowers have no petals, decorating themselves instead with many showy stamens. The woody fruits, known as gumnuts, are roughly cone-shaped and have valves at the end which open to release the seeds.

Nearly all eucalypts are evergreen but some tropical species lose their leaves at the end of the dry season. As in other members of the Myrtle family, eucalypt leaves are covered with oil glands. The copious oils produced are an important feature of the genus. Eucalypts also commonly exhibit leaf dimorphism. When young, their leaves are opposite, oval to roundish, and occasionally without a petiole. When one to a few years old, the leaves of most species become alternate, lanceolate to falcate (sickle-shaped), quite slender and pendulous with longer petioles. However there are numerous species such as E. melanophloia and E. setosa that retain the juvenile leaf form throughout their life history. The adult leaves of most species, as well as the juvenile leaves of some, are the same on both sides, lacking the distinction between upper and lower surfaces shown by the leaves of most plants. Most species do not flower until adult foliage starts to appear; E. cinerea and E. perriniana are notable exceptions.

[edit] Bark

The bark dies annually and species can be roughly grouped based on its appearance. In smooth-barked trees most of the bark is shed, leaving a smooth surface that is often colourfully mottled. With rough-barked trees the dead bark persists on the tree and dries out. Many trees, however, have smooth bark at the top but rough bark on the trunk or its base. The types of rough bark is often used to broadly label a group of eucalypts.

They are:

• Stringybark - consists of long-fibres and can be pulled off in long pieces. It is usually thick with a spongy texture.
• Ironbark - is hard, rough and deeply furrowed. It is soaked with dried kino (a sap exuded by the tree) which gives a dark red or even black colour.
• Tessellated - bark is broken up into many distinct flakes. They are corkish and can flake off.
• Box - has short fibres. Some also show tessellation.
• Ribbon - this has the bark coming off in long thin pieces but still loosely attached in some places. They can be long ribbons, firmer strips or twisted curls.

[edit] Species & Hybridism

Like most groups of plants, eucalypts have evolved over a long period. It is believed that all are related either closely or remotely. Some have diverged from the mainstream of the genus to the extent that they are quite isolated genetically and are able to be recognised by only a few relatively invariant characteristics. Most, however, may be regarded as belonging to large or small groups of related species, which are often in geographical contact with each other and between which gene exchange still occurs. In these situations many species will appear to grade into one another and intermediate forms are common. In other words, some species are relatively fixed genetically, as expressed in their morphology, while others have not diverged completely from their nearest relatives.

There are over 700 species of Eucalyptus, refer to the List of Eucalyptus species for a comprehensive list of species.

Hybrid individuals have not always been recognised as such on first collection and some have been named as new species, such as E. chrysantha (E. preissiana X E. sepulcralis) and E. "rivalis" (E. marginata X E. megacarpa). Hybrid combinations are not particularly common in the field, but come other published species have been suggested to be hybrid combinations and are frequently seen in Australia. For example, E. erythrandra is believed to be E. angulosa X E. teraptera and due to its wide distribution is often referred to in texts.^[1]

[edit] Related genera

A small genus of similar trees, Angophora, has also been known since the 18th century. In 1995 new evidence, largely genetic, indicated that some prominent eucalypt species were actually more closely related to Angophora than to the other eucalypts; they were split off into the new genus Corymbia. Although separate, the three groups are allied and it remains acceptable to refer to the members of all three genera Angophora, Corymbia and Eucalyptus as "eucalypts". The coolibah trees, referred to in Waltzing Matilda, are eucalypts E. coolabah and E. microtheca.

[edit] Tall timber

Today, specimens of the Australian Mountain Ash, Eucalyptus regnans, are among the tallest trees in the world at up to 92 metres in height ^[2] and the tallest of all flowering plants; taller trees such as the Coast Redwood are all conifers. There is credible evidence however that at the time of European settlement of Australia some Mountain Ash were indeed the tallest plants in the world.

[edit] Tolerance

Most eucalypts are not tolerant of frost, or only tolerate light frosts down to -3°C to -5°C; the hardiest, are the so-called Snow Gums such as Eucalyptus pauciflora which is capable of withstanding cold and frost down to about -20°C. Two sub-species, E. pauciflora niphophila and E. pauciflora debeuzevillei in particular are even hardier and can tolerate even quite severe winters.

Several other species, especially from the high plateau and mountains of central Tasmania such as E. coccifera, E. subcrenulata, and E. gunnii have produced extreme cold hardy forms and it is seed procured from these genetically hardy strains that are planted for ornament in colder parts of the world.

[edit] Animal relationships

An essential oil extracted from eucalypt leaves contains compounds that are powerful natural disinfectants and which can be toxic in large quantities. Several marsupial herbivores, notably koalas and some possums, are relatively tolerant of it. The close correlation of these oils with other more potent toxins called formylated phloroglucinol compounds allows koalas and other marsupial species to make food choices based on the smell of the leaves. However, it is the formylated phloroglucinol compounds that are the most important factor in choice of leaves by koalas.

Eucalypts make a lot of nectar, providing food for many insects. For example, see the list of Lepidoptera which feed on Eucalyptus.

[edit] Hazards

Some species of Eucalyptus have a habit of dropping entire branches off as they grow. Eucalyptus forests are littered with dead branches. The Australian Ghost Gum Eucalyptus papuana is also termed the "widow maker", due to the high number of pioneer tree-felling workers who were killed by falling branches. Many people have been killed as they camped underneath the trees. It is thought the trees shed very large branches to conserve water during periods of drought. This may be the real reason behind the drop bear story told to children - the idea is to keep them away from being under dangerous branches.

[edit] Fire

On warm days vapourised eucalyptus oil rises above the bush to create the characteristic distant blue haze of the Australian landscape. Eucalyptus oil is highly flammable (trees have been known to explode[1] [2]) and bush fires can travel easily through the oil-rich air of the tree crowns. The dead bark and fallen branches are also flammable. Eucalypts are well adapted for periodic fires, in fact most species are dependent on them for spread and regeneration. They do this via lignotubers, epicormic buds under the bark and from fire-germinated seeds sprouting in the ashes.

Eucalypts originated between 35 and 50 million years ago, not long after Australia-New Guinea separated from Gondwana, their rise coinciding with an increase in fossil charcoal deposits (suggesting that fire was a factor even then), but they remained a minor component of the Tertiary rainforest until about 20 million years ago when the gradual drying of the continent and depletion of soil nutrients led to the development of a more open forest type, predominantly Casuarina and Acacia species. With the arrival of the first humans about 50 thousand years ago, fires became much more frequent and the fire-loving eucalypts soon came to account for roughly 70% of Australian forest.

Eucalypts regenerate quickly after fire. After the Canberra bushfires of 2003, hectares of imported species were killed, but in a matter of weeks the gum trees were putting out suckers and looking generally healthy.

The two valuable timber trees, Alpine Ash E. delegatensis and Mountain Ash E. regnans, are killed by fire and only regenerate from seed. The same fire that has had little impact on forests around Canberra has resulted in thousands of hectares of dead ash forests. There has been some debate as to whether to leave the stands, or attempt to harvest the mostly undamaged timber.

[edit] Cultivation and uses

Eucalyptus have many uses which have made them economically important trees. Perhaps the Karri and the Yellow box varieties are the best known. Due to their fast growth the foremost benefit of these trees is the wood. They provide many desirable characteristics for use as ornament, timber, firewood and pulpwood. Fast growth also makes eucalypts suitable as windbreaks.

Eucalypts draw a tremendous amount of water from the soil through the process of transpiration. They have been planted (or re-planted) in some places to lower the water table and reduce soil salination. Eucalypts have also been used as a way of reducing malaria by draining the soil in Algeria, Sicily^[3] and also in Europe and California^[4]. Drainage removes swamps which provide a habitat for mosquito larvae, but such drainage can also destroy ecologically productive areas.

Eucalyptus oil is readily steam distilled from the leaves and can be used for cleaning, deodorising, and in very small quantities in food supplements; especially sweets, cough drops and decongestants. Eucalyptus oil has insect repellent properties (Jahn 1991 a, b; 1992), and is an active ingredient in some commercial mosquito repellents (Fradin & Day 2002).

The nectar of some eucalyptus produces high quality monofloral honey. In the western United States the flowering is in late January, before the flowering of commercial nut and fruit trees, thus it is easily segregated and the honey produced has a flavour described as "buttery^{[citation needed]}.

The ghost gum's leaves were used by Aborigines to catch fish. Soaking the leaves in water releases a mild tranquilliser which stuns fish temporarily.

Eucalyptus is also used to make the digeridoo, a musical wind instrument made popular by the Aborigines of Australia.

[edit] History

Although Eucalypts must have been seen by the very early European explorers and collectors, no botanical collections of them are known to have been made until 1770 when Joseph Banks and Daniel Solander arrived at Botany Bay with Captain James Cook. There they collected specimens of E. gummifera and later, near the Endeavour River in northern Queensland, they collected E. platyphylla; neither of these species was named as such at the time.

In 1777, on Cook's third expedition, David Nelson collected a eucalypt on Bruny Island in southern Tasmania. This specimen was taken to the British Museum in London, and it was named Eucalyptus obliqua by the French botanist L'Héritier, who was working in London at the time. He coined the generic name from the Greek roots eu and calyptos, meaning "well" and "covered" in reference to the operculum of the flower bud. This organ protects the developing flower parts as the flower develops and is shed by the pressure of the emerging stamens at flowering.

The name obliqua was derived from the Latin obliquus, meaning "oblique" which is the botanical term describing a leaf base where the two sides of the leaf blade are of unequal length and do not meet the petiole at the same place.

In naming E. obliqua, L'Héritier caused to be perpetuated, most likely by accident, a feature common to all eucalypts - the operculum. In his choice of a specific name, he recognised not only the characteristic feature of E. obliquabut onthat is common to many others as well. E. obliqua was published in 1788-89 and coincides with the date of the first official European settlement of Australia.

Between 1788-89 and the turn of the ninteenth century several more species of Eucalyptus were named and published. Most of these were by the English botanist James Edward Smith and most were, as might be expected, trees of the Sydney region. These include the economically valuable E. pilularis, E. saligna and E. tereticornis.

The ninteenth century saw the endeavours of several of the great botanists in Australian history, particularly Ferdinand von Mueller, whose work on eucalypts contributed greatly to the first comprehensive account of the genus in George Bentham's Flora Australiensis in 1867 - which today remains the only complete Australian flora. The account in Bentham is the most important early systematic treatment of the genus.

Bentham divided the genus into five series whose distinctions were based on characteristics of the stamens, particularly the anthers (Mueller, 1879-84), while Joseph Henry Maiden (1824) elaborated in the anther system (Maiden, 1903-33), and this was taken even further by William Faris Blakely (1934). By this time the anther system had become too complex to be workable.

The first endemic Western Australian eucalypt to be collected and subsequently named was the yate (E. cornuta) by the French botanist La Billardiére, who collected in what is now the Esperance area in 1792.^[5]

[edit] Plantation and ecological problems

Eucalyptus were first introduced to the rest of the world by Sir Joseph Banks, botanist on the Cook expedition in 1770. They have subsequently been introduced to many parts of the world, notably California, Brazil, Ecuador, Ethiopia, Morocco, Portugal, South Africa, Israel, Galicia and Chile. Several species have become invasive and are causing major problems for local ecosystems. In Spain, they have been planted in pulpwood plantations, replacing native oak woodland. As in other such areas, while the original woodland supports numerous species of native animal life (insects, birds, salamanders, etc.), the eucalypt groves are inhospitable to the local wildlife which is not adapted to them, leading to silent forests and the decline of wildlife populations. On the other hand, eucalyptus are the basis for several industries, such as sawmilling, pulp, charcoal and others.

[edit] California

In the 1850s many Australians traveled to California to take part in the California Gold Rush. Much of California has similar climate to parts of Australia and some people got the idea of introducing eucalyptus. By the early 1900s thousands of acres of eucalyptus were planted with the encouragement of the state government. It was hoped that they would provide a renewable source of timber for construction and furniture making. However this did not happen partly because the trees were cut when they were too young and partly because the Americans did not know how to process the cut trees to prevent the wood from twisting and splitting.[3]

One way in which the eucalyptus, mainly the blue gum E. globulus, proved valuable in California was in providing windbreaks for highways, orange groves, and other farms in the mostly treeless central part of the state. They are also admired as shade and ornamental trees in many cities and gardens.

Eucalyptus forests in California have been criticized because they drive out the native plants and do not support native animals. Fire is also a problem. The 1991 Oakland Hills firestorm which destroyed almost 3,000 homes and killed 25 people was partly fueled by large numbers of eucalyptus in the area close to the houses.[4]

In some parts of California eucalyptus forests are being removed and native trees and plants restored. Individuals have also illegally destroyed some trees and are suspected of introducing insect pests from Australia which attack the trees.[5]

[edit] Brazil

In 1910 Eucalyptus was introduced to Brazil for timber substitution and the vegetal coal industry. Regrettably the ecological effects weren't studied and today Eucalyptus is causing soil problems due to its high consumption of water and consequent exhaustion of some water tables. This has turned rich soil into desert-like soil and destroyed the native flora, causing food chain imbalance and encouraging vast growth in the populations of some insects (such as ants and termites).

[edit] Ethiopia

This species was introduced to Ethiopia in either 1894 or 1895, either by Emperor Menelik II's French advisor Mondon-Vidailhet or the Englishman Captain O'Brian. Due to massive deforestation around his new capital city Addis Ababa caused by a growing appetite for fire wood, Emperor Menelik II was came to endorse its planting around that city; according to Richard R.K. Pankhurst, "The great advantage of the eucalyptus was that it was fast growing, required little attention and when cut down grew up again from the roots; it could be harvested every ten years. The tree proved successful from the onset".^[6] Plantations of eucalyptus spread from the capital to other growing urban centers such as Debre Marqos; Pankhurst reports that the most common species found in Addis Ababa in the mid-1960s was E. globulus, although he also found E. melliodora and E. rostrata in significant numbers.

As in Brazil, the thirst of the eucalyptus "tended to dry up rivers and wells". Popular opposition soon developed that in 1913 a proclamation was issued ordering a partial destruction of all standing trees, and their repalcement with mulberry trees. "The proclamation," Pankhurst notes, "however remained a dead letter; there is no evidence of eucalyptus being uprooted, still less of mulberry trees being planted."^[7] The eucalyptus remains a defining feature of Addis Ababa.

[edit] References

[edit] External links

Find more information on Eucalyptus by searching Wikipedia's sister projects
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• EUCLID Sample, CSIRO
• The Eucalyptus Page
• EucaLink
• Currency Creek Arboretum - Eucalypt Research
• Eucalyptus globulus Diagnostic photos: tree, leaves, bark
• [6] Duke, James A. Handbook of Energy Crops. 1983.
• [7] Henter, Heather. "Tree Wars: The Secret Life of Eucalyptus"
• [8] Santos, Robert. "The Eucalyptus of Califonia: Seeds of Good or Seeds of Evil?" 1997 Denair, CA : Alley-Cass Publications
• [9] Williams, Ted. "America's Largest Weed" Audubon Magazine, January 2002

Medicinal resources, eucalyptus essential oil:

http://www.botanical.com/botanical/mgmh/e/eucaly14.html http://www.henriettesherbal.com/eclectic/bpc1911/eucalyptus_oleu.html

[edit] Photo gallery

Eucalyptus forest in East Gippsland, Victoria. Mostly Eucalyptus albens (white box).	Eucalyptus forest in East Gippsland, Victoria. Mostly Eucalyptus albens (white box).	Eucalyptus forest in East Gippsland, Victoria. Mostly Eucalyptus albens (white box).	A eucalyptus tree with the sun shining through its branches.
Eucalyptus bridgesiana (Apple box) on Red Hill, Australian Capital Territory.	Eucalyptus gunnii planted in southern England. The lower part of the trunk is covered in ivy.	Eucalyptus cinerea x pulverulenta - National Botanical Gardens Canberra	Eucalyptus leuxoxylon 'Rosea'
Eucalyptus gall	Eucalyptus grandis. Province of Buenos Aires, Argentina.