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*Eucalyptus*
Paper Making Properties Eucalyptus Trees, Woods and Pulp Fibres
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Eucalyptus is a diverse genus of trees (rarely shrubs), the members of which dominate the tree flora of Australia. There are almost 600 species of Eucalyptus, mostly native to Australia, with a very small number found in adjacent parts of New Guinea and Indonesia. Eucalypts can be found in almost every part of the continent, adapted to all of Australia's
climatic conditions; in fact, no other continent is so characterised by a single genus of tree as Australia is by eucalypts. Many, but far from all, are known as gum trees; other names for various species include mallee, box, ironbark, stringybark, and ash.
Eucalyptus - Overview
All eucalypts are evergreen, although some species have deciduous bark. An essential oil extracted from eucalyptus 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 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.
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) and bush fires can travel easily through the oil-rich air of the tree crowns. Eucalypts are well adapted for periodic fires, in fact most species are dependent on it for spread and regeneration: both from reserve 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.
The name Eucalyptus means "well-covered"; it describes the bud cap. A small genus of similar trees, Angophora, have 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".
Specimens of the Australian Mountain-ash, Eucalyptus regnans, are among the tallest trees in the world at 92 metres tall (Forestry Tasmania; pdf file), making them the tallest of all flowering plants; other taller trees such as the Coast Redwood are all conifers.
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 continental type 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.
Eucalypts exhibit leaf dimorphism. When young, the leaves are opposite and often roundish and occasionally without petiole. When several years old, the leaves become quite slender and with long petiole. Plants do not flower until adult foliage start to appear, except in E. cinerea.
The Coolibah tree of Waltzing Matilda is a eucalyptus, E. microtheca or E. coolabah.
Eucalypts support the larvae of a number of Lepidoptera species - see list of Lepidoptera which feed on Eucalyptus.
Angophora, Corymbia
Eucalyptus - Fire
Eucalypts regenerate very quickly after fire. After the 2000 Canberra fires, hectares of imported species were killed, whereas in a matter of weeks the gum trees were putting out suckers and looking generally cheerful. Gum trees are also very accomplished at scavenging water at the expense of other plants.
However, the two valuable timber trees E. regnans and E. delegatensis are killed by fire and only regenerate from seed. The same fire that has had little impact on forests around Canberra have 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.
Eucalypts regenerate very quickly after fire. After the 2000 Canberra fires, hectares of imported species were killed, whereas in a matter of weeks the gum trees were putting out suckers and looking generally cheerful. Gum trees are also very accomplished at scavenging water at the expense of other plants.
However, the two valuable timber trees E. regnans and E. delegatensis are killed by fire and only regenerate from seed. The same fire that has had little impact on forests around Canberra have 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.
Eucalyptus - Hazards
Eucalypts 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 deaths were actually caused by simply camping under them, as they shed whole and very large branches to conserve water during periods of drought. For this reason, one never sets up camp under an overhanging branch. This may be the real reason behind the drop bear story told to children - the idea is to keep them away from under dangerous branches.
The ghost gum's leaves were used by Aborigines to catch fish. Soaking the leaves in water releases a mild tranquiliser which stuns fish temporarily.
Eucalypts 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 deaths were actually caused by simply camping under them, as they shed whole and very large branches to conserve water during periods of drought. For this reason, one never sets up camp under an overhanging branch. This may be the real reason behind the drop bear story told to children - the idea is to keep them away from under dangerous branches.
The ghost gum's leaves were used by Aborigines to catch fish. Soaking the leaves in water releases a mild tranquiliser which stuns fish temporarily.
Eucalyptus - Ecologically disruptive as an imported exotic
Eucalypts 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, Morocco, Portugal, South Africa, Israel and Galicia. The uses they are put to include ornament, timber, firewood and (especially) pulpwood. Several species have become invasive and are causing major problems for local ecologies. 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 eucalyptus groves are inhospitable to the local wildlife which is not adapted to them, leading to silent forests and the decline of wildlife populations.
Their importation into California has been beneficial in only very limited circumstances, primarily in their use as windbreaks enclosing large tracts of arid western San Joaquin valley farmland. While some of the Australian gumwoods make a beautiful
Eucalyptus - Cultivation and uses
Eucalyptus oil is readily 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.
The Nilgiris
The Nilgiris or Blue Mountains, often called The Queen of Hills are a range of mountains and a district in the south-Indian states of Tamil Nadu and Kerala. The highest point is the mountain of Dodda Betta (also written Doddabetta), with a height of 2637m. Tea is grown at elevations of 1,000 to above 2,500 metres. The area also produces eucalyptus oil and temperate zone vegetables. Parts of many Indian movies are filmed in the Nilgiris.
The altitude of the Nilgiris results in a much cooler wetter climate than the surrounding plains, and so the area is popular as a retreat from the summer heat. The rolling hills of the Downs look very similar to the Downs in Southern England and were used for similar activities such as hunting.
The principal town of the area is Udhagamandalam, although the old British name of Ootacamund, shortened to Ooty, is often used. In the town there are many buildings which look very "British", in particular the Churches. There is even a road junction known as Charing Cross.
The other main towns in the Nilgiris are Coonoor and Kotagiri.
Wood pulp - History
Using wood to make paper is a fairly recent innovation. In the 1800s, fiber crops such as linen fibres were the primary material source, but a shortage led to experimentation with other materials. Around 1850, a German named Friedrich Gottlob Keller crushed wood with a wet grindstone to obtain wood pulp. Further experimentation by American chemist C.B. Tilghman and Swedish inventor C.F. Dahl enabled the manufacture of wood pulp using chemicals to break down the fibres. The use of wood pulp (and the introduction of steam power to the printing and paper making processes) led to cheaper paper and to the arrival of a new literary genre which we would later coin pulp fiction but were known to their contemporaries as dime novels or penny dreadfuls.
Wood pulp
Wood pulp is the most common material used to make paper. The timber resources used to make wood pulp are referred to as pulpwood. Wood pulp generally comes from softwood trees such as spruce, pine, fir, larch and hemlock, but also some hardwoods such as eucalyptus and birch.
Wood pulp - Manufacture of wood pulp
Wood pulp is made in several stages:
1. First the bark is removed from the wood. This can be done with or without water (wet stripping). The bark is generally recovered to use as fuel in the pulp and paper making process.
2. The cellulose fibres that keep the wood together are then separated. This can be done in a number of ways:
o The wood can be crushed with grinders
(huge grindstones) and then soaked in water to produce groundwood (GW). Mechanical pulps are used for products that require less strength, such as newsprint and paperboards.
o The wood can be crushed with refiners using steam at high pressures and temperatures to produce thermomechanical pulp (TMP). TMP differs in quality from groundwood.
o In additional to the refiners, chemicals can be used to break up the cellulose fibres. Pulp produced this way is known as chemithermomechanical pulp (CTMP). GW, TMP and CTMP are all considered as mechanical pulps. The mechanical pulps tend to turn yellow in time, because of the binding material, lignin, in the pulp.
o Chemical pulp is produced by combining wood chips and chemicals in huge vats known as digesters. The effect of the heat and the chemicals dissolves the lignin, that binds the cellulose fibers together, without breaking the wood fibres. The fluid that contains lignin and other dissolved material is then dried and used as fuel. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. Chemical pulps include kraft pulp (or sulphate pulp).
o Pulp can also be made out of waste paper and paperboard. Recycled pulp is most often used to make paperboard, newsprint or sanitary paper.
o Research is under way to develop biological pulping, similar to chemical pulping but using certain species of fungi that are able to break down the unwanted lignin, but not the cellulose fibres. This could have major environmental benefits in reducing the pollution associated with chemical pulping.
3. The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorine, such as oxygen, ozone and Hydrogen peroxide
4. The pulp mixture is now sent to the paper machine, where it is shaped and dried.
