Aeucalyptus (/ˌjuːkəˈlɪptəs/)[3] is a plant in thegenusEucalyptus, which consists of more than 700 species offlowering plants in the familyMyrtaceae. Most species of eucalyptus are trees, oftenmallees, and a few are shrubs. Along with several other genera in the tribeEucalypteae, includingCorymbia andAngophora, they are commonly known aseucalypts or "gum trees". Eucalyptuses have bark that is either smooth, fibrous, hard, or stringy and leaves that have oilglands. Thesepals andpetals are fused to form a "cap" oroperculum over thestamens, hence the name from Greekeû ("well") andkaluptós ("covered").[4] The fruit is a woodycapsule commonly referred to as a "gumnut".
Most species of eucalyptus arenative to Australia, and every state and territory has representative species. About three-quarters of Australian forests are eucalypt forests. Many eucalypt species have adapted towildfire,[clarification needed] are able to resprout after fire, or have seeds that survive fire.[citation needed]
A few species are native to islands north of Australia, and a smaller number are only found outside the continent. Eucalypts have been grown in plantations in many other countries because they are fast-growing, have valuable timber, or can be used forpulpwood,honey production, oressential oils. In some countries, however, they have been removed because of the danger offorest fires due to their high flammability.
Eucalypts vary in size andhabit from shrubs to tall trees. Trees usually have a single main stem ortrunk but many eucalypts are mallees that are multistemmed from ground level and rarely taller than 10 metres (33 feet). There is no clear distinction between a mallee and a shrub but in eucalypts, a shrub is a mature plant less than 1 m (3 ft 3 in) tall and growing in an extreme environment.Eucalyptus vernicosa in theTasmanian highlands,E. yalatensis on theNullarbor andE. surgens growing on coastal cliffs inWestern Australia are examples of eucalypt shrubs.[5]
The terms "mallet" and "marlock" are only applied toWestern Australian eucalypts. A mallet is a tree with a single thin trunk with a steeply branching habit but lacks both alignotuber andepicormic buds.Eucalyptus astringens is an example of a mallet. A marlock is a shrub or small tree with a single, short trunk, that lacks a lignotuber and has spreading, densely leafy branches that often reach almost to the ground.Eucalyptus platypus is an example of a marlock.[5][6][7]
Eucalyptus trees, including mallets and marlocks, are single-stemmed and includeEucalyptus regnans, the tallest known flowering plant on Earth.[8] The tallest reliably measured tree in Europe,Karri Knight, can be found inCoimbra, Portugal in Vale de Canas. It is aEucalyptus diversicolor of 72.9 meters height and of 5.71 meters girth.[9]
All eucalypts add a layer ofbark every year and the outermost layer dies. In about half of the species, the dead bark is shed exposing a new layer of fresh, living bark. The dead bark may be shed in large slabs, in ribbons or in small flakes. These species are known as "smooth barks" and includeE. sheathiana,E. diversicolor,E. cosmophylla andE. cladocalyx. The remaining species retain the dead bark which dries out and accumulates. In some of these species, the fibres in the bark are loosely intertwined (in stringybarks such asE. macrorhyncha or peppermints such asE. radiata) or more tightly adherent (as in the "boxes" such asE. leptophleba). In some species (the "ironbarks" such asE. crebra andE. jensenii) the rough bark is infused with gum resin.[5]
Many species are 'half-barks' or 'blackbutts' in which the dead bark is retained in the lower half of the trunks or stems—for example,E. brachycalyx,E. ochrophloia, andE. occidentalis—or only in a thick, black accumulation at the base, as inE. clelandii. In some species in this category, for exampleE. youngiana andE. viminalis, the rough basal bark is very ribbony at the top, where it gives way to the smooth upper stems. The smooth upper bark of the half-barks and that of the completely smooth-barked trees and mallees can produce remarkable colour and interest, for exampleE. deglupta.[11]
E. globulus bark cells are able to photosynthesize in the absence of foliage, conferring an "increased capacity to re-fix internal CO2 following partial defoliation".[12] This allows the tree to grow in less-than-ideal climates, in addition to providing a better chance of recovery from damage sustained to its leaves in an event such as a fire.[13]
Different commonly recognised types of bark include:[citation needed]
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 impregnated with driedkino (asap exuded by the tree) which gives a dark red or even black colour.
Tessellated—bark is broken up into many distinct flakes. They arecorkish and can flake off.
Box—has short fibres. Some also show tessellation.
Ribbon—has the bark coming off in long, thin pieces, but is still loosely attached in some places. They can be long ribbons, firmer strips, or twisted curls.
Nearly all eucalyptuses areevergreen, but some tropical species lose their leaves at the end of the dry season. As in other members of themyrtle family, eucalyptus leaves are covered with oil glands. The copious oils produced are an important feature of the genus. Although mature eucalyptus trees may be towering and fully leafed, their shade is characteristically patchy because the leaves usually hang downwards.[citation needed]
The leaves on a mature eucalyptus plant are commonlylanceolate,petiolate, apparentlyalternate and waxy or glossy green. In contrast, the leaves of seedlings are oftenopposite,sessile andglaucous. But many exceptions to this pattern exist. Many species such asE. melanophloia andE. setosa retain the juvenile leaf form even when the plant is reproductively mature. Some species, such asE. macrocarpa,E. rhodantha, andE. crucis, are sought-after ornamentals due to this lifelong juvenile leaf form. A few species, such asE. petraea,E. dundasii, andE. lansdowneana, have shiny green leaves throughout their life cycle.Eucalyptus caesia exhibits the opposite pattern of leaf development to most eucalyptuses, with shiny green leaves in the seedling stage and dull, glaucous leaves in mature crowns. The contrast between juvenile and adult leaf phases is valuable in field identification.[citation needed]
Four leaf phases are recognised in the development of a eucalyptus plant: the 'seedling', 'juvenile', 'intermediate', and 'adult' phases. However, no definite transitional point occurs between the phases. The intermediate phase, when the largest leaves are often formed, links the juvenile and adult phases.[11]
In all except a few species, the leaves form in pairs on opposite sides of a square stem, consecutive pairs being at right angles to each other (decussate). In some narrow-leaved species, for exampleE. oleosa, the seedling leaves after the second leaf pair are often clustered in a detectablespiral arrangement about a five-sided stem. After the spiral phase, which may last from several to many nodes, the arrangement reverts to decussate by the absorption of some of the leaf-bearing faces of the stem. In those species with opposite adult foliage the leaf pairs, which have been formed opposite at the stem apex, become separated at their bases by unequal elongation of the stem to produce the apparently alternate adult leaves.[citation needed]
The most readily recognisable characteristics of eucalyptus species are the distinctive flowers and fruit (capsules or "gumnuts"). Flowers have numerous fluffystamens which may be white, cream, yellow, pink, or red; in bud, the stamens are enclosed in a cap known as anoperculum which is composed of the fused sepals or petals, or both. Thus, flowers have no petals, but instead decorate themselves with the many showy stamens. As the stamens expand, the operculum is forced off, splitting away from the cup-like base of the flower; this is one of the features that unites the genus. The woody fruits or capsules are roughly cone-shaped and have valves at the end which open to release the seeds, which are waxy, rod-shaped, about 1 mm in length, and yellow-brown in colour. Most species do not flower until adult foliage starts to appear;E. cinerea andE. perriniana are notable exceptions.[citation needed]
The genusEucalyptus was first formally described in 1789 byCharles Louis L'Héritier de Brutelle who published the description in his bookSertum Anglicum, seu, Plantae rariores quae in hortis juxta Londinum along with a description of thetype species,Eucalyptus obliqua.[14][15] The nameeucalyptus is derived from theAncient Greek words "eu" meaning 'well' and "calyptos" 'covered', referring to theoperculum covering the flower buds.[5][16][17]
The type specimen was collected in 1777 byDavid Nelson, the gardener-botanist onCook'sthird voyage. He collected the specimen onBruny Island and sent it to de Brutelle who was working inLondon at that time.[5]
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 whenJoseph Banks andDaniel Solander arrived atBotany Bay withCaptain James Cook. There they collected specimens ofE. gummifera and later, near theEndeavour River in northernQueensland,E. platyphylla; neither of these species was named as such at the time.[citation needed]
In 1777, on Cook's third expedition, David Nelson collected a eucalypt onBruny Island in southernTasmania. This specimen was taken to theBritish Museum inLondon, and was namedEucalyptus obliqua by the French botanistL'Héritier, who was working in London at the time.[18] He coined the generic name from the Greek rootseu andcalyptos, meaning "well" and "covered" in reference to theoperculum of the flower bud which protects the developing flower parts as the flower develops and is shed by the pressure of the emergingstamens at flowering.[4]
The nameobliqua was derived from the Latinobliquus, meaning "oblique", which is thebotanical term describing aleaf base where the two sides of the leaf blade are of unequal length and do not meet the petiole at the same place.[citation needed]
E. obliqua was published in 1788–89, which coincided with the European colonisation of Australia. Between then and the turn of the 19th century, several more species of eucalyptus were named and published. Most of these were by the English botanistJames Edward Smith and most were, as might be expected, trees of theSydney region. These include the economically valuableE. pilularis,E. saligna andE. tereticornis.[citation needed]
The first endemic Western Australian eucalyptus to be collected and subsequently named was the Yate (E. cornuta) by the French botanistJacques Labillardière, who collected in what is now theEsperance area in 1792.[11]
Several Australian botanists were active during the 19th century, particularlyFerdinand von Mueller, whose work oneucalypts contributed greatly to the first comprehensive account of the genus inGeorge Bentham'sFlora Australiensis in 1867. The account is the most important early systematic treatment of the genus. Bentham divided it into five series whose distinctions were based on characteristics of the stamens, particularly the anthers (Mueller, 1879–84), work elaborated byJoseph Henry Maiden (1903–33) and still further byWilliam Faris Blakely (1934). The anther system became too complex to be workable and more recent systematic work has concentrated on the characteristics of buds, fruits, leaves and bark.
Over 700species of eucalyptus are known. Some havediverged from the mainstream of thegenus to the extent that they are quite isolatedgenetically 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 whichgene exchange still occurs. In these situations, many species appear to grade into one another, and intermediate forms are common. In other words, some species are relatively fixed genetically, as expressed in theirmorphology, while others have not diverged completely from their nearest relatives.[citation needed]
Hybrid individuals have not always been recognised as such on first collection and some have been named as new species, such asE. chrysantha (E. preissiana ×E. sepulcralis) andE. "rivalis" (E. marginata ×E. megacarpa). Hybrid combinations are not particularly common in the field, but some other published species frequently seen in Australia have been suggested to be hybrid combinations. For example,Eucalyptus × erythrandra is believed to beE. angulosa ×E. teraptera and due to its wide distribution is often referred to in texts.[11]
Eucalyptus regnans exceeding 80 metres (260 ft), in an area of extensive logging, Tasmania
Eucalyptus is one of three similargenera that are commonly referred to as "eucalypts", the others beingCorymbia andAngophora. Many species, though by no means all, are known as gum trees because they exude copiouskino from any break in thebark (e.g.,scribbly gum). The generic name is derived from theGreek words ευ (eu) "well" and καλύπτω (kalýpto) "to cover", referring to theoperculum on thecalyx that initially conceals theflower.[21]
According toPlants of the World Online, there are more than 715 species of plants in the genusEucalyptus and most are native to Australia; a very small number are found in adjacent areas ofNew Guinea andIndonesia.[22] One species,Eucalyptus deglupta, ranges as far north as thePhilippines. Of the 15 species found outside Australia, just nine are exclusively non-Australian. Species of eucalyptus are cultivated widely in the tropical and temperate world, including theAmericas,Europe,Africa, theMediterranean Basin, theMiddle East,China, and theIndian subcontinent. However, the range over which many eucalypts can be planted in the temperate zone is constrained by their limited cold tolerance.[23]
Australia is covered by 92,000,000 hectares (230,000,000 acres) of eucalypt forest, comprising three quarters of the area covered by native forest.[24] TheBlue Mountains of southeastern Australia have been a centre of eucalypt diversification;[25] their name is in reference to the blue haze prevalent in the area, believed derived from the volatileterpenoids emitted by these trees.[26]
The oldest definitive eucalyptus fossils are fromPatagonia inSouth America, where eucalypts are no longer native, though they have been introduced from Australia. The fossils are from the earlyEocene (51.9 Mya), and were found in theLaguna del Hunco Formation inChubut Province inArgentina.[27][28] This shows that the genus had aGondwanan distribution. Fossil leaves also occur in the Miocene of New Zealand, where the genus is not native today, but again have been introduced from Australia.[29]
Despite the prominence of eucalyptuses in modern Australia, estimated to contribute some 75% of the modern vegetation, the fossil record is very scarce throughout much of theCenozoic, and suggests that this rise to dominance is a geologically more recent phenomenon. The oldest reliably dated macrofossil of the eucalyptus is a 21-million-year-old tree-stump encased in basalt in the upper Lachlan Valley inNew South Wales. Other fossils have been found, but many are either unreliably dated or else unreliably identified.[30]
It is useful to consider where eucalyptus fossils have not been found. Extensive research has gone into the fossil floras of thePaleocene toOligocene of South-Eastern Australia, and has failed to uncover a single eucalyptus specimen. Although the evidence is sparse, the best hypothesis is that in the mid-Tertiary, the continental margins of Australia only supported more mesic noneucalypt vegetation, and that eucalypts probably contributed to the drier vegetation of the arid continental interior. With the progressive drying out of the continent since theMiocene, eucalypts were displaced to the continental margins, and much of the mesic and rainforest vegetation that was once there was eliminated.[30]
The current superdominance of eucalyptus in Australia may be an artefact of human influence on its ecology. In more recent sediments, numerous findings of a dramatic increase in the abundance of eucalyptus pollen are associated with increased charcoal levels. Though this occurs at different rates throughout Australia, it is compelling evidence for a relationship between the artificial increase of fire frequency with the arrival of Aboriginals and increased prevalence of this exceptionally fire-tolerant genus.[30]
Most eucalypts are not tolerant of severe cold.[23][32][33] Eucalypts do well in a range of climates but are usually damaged by anything beyond a light frost of −5 °C (23 °F);[23][32][33] the hardiest are the snow gums, such asEucalyptus pauciflora, which is capable of withstanding cold and frost down to about −20 °C (−4 °F).[34] Two subspecies,E. pauciflora subsp. niphophila andE. pauciflora subsp. debeuzevillei in particular are even hardier and can tolerate even quite severe winters. Several other species, especially from the high plateau and mountains of centralTasmania such asEucalyptus coccifera,Eucalyptus subcrenulata andEucalyptus gunnii,[35] have also produced extreme cold-hardy forms and it is seed procured from thesegenetically hardy strains that are planted for ornament in colder parts of the world.
Anessential oil extracted from eucalyptus leaves contains compounds that are powerful natural disinfectants and can be toxic in large quantities. Severalmarsupial herbivores, notablykoalas and somepossums, are relatively tolerant of it. The close correlation of these oils with other more potent toxins called formylatedphloroglucinol compounds (euglobals,macrocarpals andsideroxylonals)[36] allows koalas and othermarsupial species to make food choices based on the smell of the leaves. For koalas, these compounds are the most important factor in leaf choice.
A wide variety of insects also feed exclusively on eucalyptus leaves, such as beetles in the genusParopsisterna.[37]
Theeusocial beetleAustroplatypus incompertus makes and defends its galleries exclusively inside eucalypts, including some species of eucalyptus andCorymbia.[38]
Eucalypts originated between 35 and 50 million years ago, not long afterAustralia-New Guinea separated fromGondwana, 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, predominantlyCasuarina andAcacia species.[citation needed]
The two valuable timber trees, alpine ashE. delegatensis and Australian mountain ashE. regnans, are killed by fire and only regenerate from seed. The same 2003 bushfire that had little impact on forests aroundCanberra resulted in thousands of hectares of dead ash forests. However, a small amount of ash survived and put out new ash trees as well.[citation needed]
Eucalyptus oil is highly flammable and at high enough temperatures the oil expands quickening the spread of wildfires.[44][45]Bushfires can travel easily through the oil-rich air of the tree crowns.[46][47] Eucalypts obtain long-term fire survivability from their ability to regenerate fromepicormic buds situated deep within their thick bark, or fromlignotubers,[48] or by producingserotinous fruits.[49]
In seasonally dry climates oaks are often fire-resistant, particularly in open grasslands, as a grass fire is insufficient to ignite the scattered trees. In contrast, a eucalyptus forest tends to promote fire because of the volatile and highly combustible oils produced by the leaves, as well as the production of large amounts oflitter high in phenolics, preventing its breakdown byfungi and thus accumulating as large amounts of dry, combustible fuel.[48] Consequently, dense eucalypt plantings may be subject to catastrophic firestorms. In fact, almost thirty years before theOakland firestorm of 1991, a study of eucalyptuses in the area warned that the litter beneath the trees builds up very rapidly and should be regularly monitored and removed.[50] It has been estimated that 70% of the energy released through the combustion of vegetation in the Oakland fire was due to eucalyptuses.[51] In aNational Park Service study, it was found that the fuel load (in tons per acre) of non-native eucalyptus woods is almost three times as great as native oak woodland.[51]
DuringWorld War II, one California town cut down their eucalyptus trees to "about a third of their height in the vicinity ofanti-aircraft guns" because of the known fire-fueling qualities of the trees, with the mayor telling a newspaper reporter, "If ashell so much as hits a leaf, it's supposed to explode."[52]
Some species of eucalyptus drop branches unexpectedly. In Australia,Parks Victoria warns campers not to camp underriver red gums.[53] Some councils in Australia such asGosnells, Western Australia, have removed eucalypts after reports of damage from dropped branches, even in the face of lengthy, well publicised protests to protect particular trees.[54] A former Australian National Botanic Gardens director and consulting arborist, Robert Boden, has been quoted referring to "summer branch drop".[55] Dropping of branches is recognised in Australia literature through the fictional death of Judy inSeven Little Australians. Although all large trees can drop branches, the density of eucalyptus wood is high[56] due to its high resin content,[57] increasing the hazard.
Eucalypts were introduced fromAustralia to the rest of the world following theCook expedition in 1770. Collected bySir Joseph Banks,botanist on the expedition, they were subsequently introduced to many parts of the world, notablyCalifornia, southern Europe, Africa, theMiddle East, South Asia and South America. About 250 species are under cultivation in California.[58] InPortugal and alsoSpain, eucalypts have been grown in plantations for the production ofpulpwood. Eucalyptuses are the basis for several industries, such as sawmilling, pulp, charcoal and others. Several species have becomeinvasive and are causing major problems for local ecosystems, mainly due to the absence ofwildlife corridors and rotations management.[citation needed]
Eucalypts have many uses which have made themeconomically important trees, and they have become acash crop in poor areas such asTimbuktu, Mali[59]: 22 and thePeruvianAndes,[60] despite concerns that the trees areinvasive in some environments like those ofSouth Africa.[61] Best-known are perhaps the varietieskarri andyellow box. Due to their fast growth, the foremost benefit of these trees is their wood. They can be chopped off at the root and grow back again. They provide many desirable characteristics for use asornament, timber, firewood and pulpwood. Eucalyptus wood is also used in a number of industries, from fence posts (where the oil-rich wood's high resistance to decay is valued) and charcoal tocellulose extraction forbiofuels. Fast growth also makes eucalypts suitable aswindbreaks and to reduceerosion.[citation needed][62]
Some eucalyptus species have attracted attention from horticulturists,global development researchers, and environmentalists because of desirable traits such as being fast-growing sources of wood, producing oil that can be used for cleaning and as a naturalinsecticide, or an ability to be used to drainswamps and thereby reduce the risk ofmalaria.Eucalyptus oil finds many uses like in fuels, fragrances, insect repellence and antimicrobial activity.Eucalyptus trees showallelopathic effects; they release compounds which inhibit other plant species from growing nearby. Outside their natural ranges, eucalypts are both lauded for their beneficial economic impact on poor populations[60][59]: 22 and criticised for being "water-guzzling"aliens,[61] leading to controversy over their total impact.[44]
Eucalypts draw a tremendous amount of water from the soil through the process oftranspiration. They have been planted (or re-planted) in some places to lower thewater table and reducesoil salination. Eucalypts have also been used as a way of reducingmalaria by draining the soil in Algeria, Lebanon, Sicily,[63] elsewhere inEurope, in the Caucasus (WesternGeorgia), and California.[64] Drainage removesswamps which provide a habitat formosquitolarvae, but can also destroy ecologically productive areas. This drainage is not limited to the soil surface, because theEucalyptus roots are up to 2.5 m (8 ft 2 in) in length and can, depending on the location, even reach thephreatic zone.[citation needed]
Eucalyptus is the most common short fibre source forpulpwood to makepulp.[65] The types most often used inpapermaking areEucalyptus globulus (in temperate areas) and theEucalyptus urophylla xEucalyptus grandis hybrid (in the tropics).[66] The fibre length ofEucalyptus is relatively short and uniform with low coarseness compared with other hardwoods commonly used as pulpwood. The fibres are slender, yet relatively thick walled. This gives uniform paper formation and highopacity that are important for all types offine papers. The low coarseness is important for high qualitycoated papers.[65]Eucalyptus is suitable for manytissue papers as the short and slender fibres gives a high number of fibres per gram and low coarseness contributes to softness.[65]
Eucalyptus oil is readilysteam distilled from the leaves and can be used for cleaning and as an industrial solvent, as an antiseptic, for deodorising, and in very small quantities infood supplements, especiallysweets,cough drops,toothpaste and decongestants. It has insect-repellent properties,[67] and serves as an active ingredient in some commercial mosquito-repellents.[68]Aromatherapists have adoptedEucalyptus oils for a wide range of purposes.[69]Eucalyptus globulus is the principal source ofEucalyptus oil worldwide.
Eucalypt wood is also commonly used to makedidgeridoos, a traditionalAustralian Aboriginalwind instrument.[70] The trunk of the tree is hollowed out by termites, and then cut down if the bore is of the correct size and shape.[71]
Eucalypt wood is also being used as atonewood and a fingerboard material for acoustic guitars, notably by the California-based Taylor company.[72]
All parts ofEucalyptus may be used to makedyes that are substantive onprotein fibres (such assilk andwool), simply by processing the plant part withwater. Colours to be achieved range from yellow and orange through green, tan, chocolate and deep rust red.[73]
Eucalyptus trees in the Australian outback draw up gold from tens of metres underground through their root system and deposit it as particles in their leaves and branches. A Maia detector for x-ray elemental imaging at theAustralian Synchrotron clearly showed deposits of gold and other metals in the structure ofEucalyptus leaves from the Kalgoorlie region of Western Australia that would have been untraceable using other methods. The microscopic leaf-bound "nuggets", about 8micrometres wide on average, are not worth collecting themselves, but may provide an environmentally benign way of locating subsurface mineral deposits.[74][75]
In the 20th century, scientists around the world experimented withEucalyptus species. They hoped to grow them in the tropics, but most experimental results failed until breakthroughs in the 1960s-1980s in species selection, silviculture, and breeding programs "unlocked" the potential of eucalypts in the tropics. Prior to then, as Brett Bennett noted in a 2010 article, eucalypts were something of the "El Dorado" of forestry. Today,Eucalyptus is the most widely planted type of tree in plantations around the world,[76] inSouth America (mainly inBrazil,Argentina,Paraguay andUruguay),South Africa,Australia,India,Galicia,Portugal and many more.[77]
In the 1850s,Eucalyptus trees were introduced toCalifornia by Australians during theCalifornia Gold Rush. Much of California is similar in climate to parts of Australia. By the early 1900s, thousands of acres of eucalypts were planted with the encouragement of the state government. It was hoped that they would provide a renewable source of timber for construction, furniture making andrailway sleepers. It was soon found that for the latter purposeEucalyptus was particularly unsuitable, as the ties made fromEucalyptus had a tendency to twist while drying, and the dried ties were so tough that it was nearly impossible to hammerrail spikes into them.[78]
They went on to note that the promise ofEucalyptus in California was based on the old virgin forests of Australia. This was a mistake, as the young trees being harvested in California could not compare in quality to the centuries-oldEucalyptus timber of Australia. It reacted differently to harvest. The older trees didn't split or warp as the infant California crop did. There was a vast difference between the two, and this would doom the CaliforniaEucalyptus industry.[78]
The speciesE. camaldulensis,E. tereticornis, andE. cladocalyx are all present in California, but the blue gumE. globulus makes up by far the largest population in the state.[79] One way in which theEucalyptus, mainly the blue gumE. globulus, proved valuable in California was in providing windbreaks for highways, orange groves, and farms in the mostly treelesscentral part of the state. They are also admired as shade and ornamental trees in many cities and gardens.[citation needed]
Eucalyptus plantations in California have been criticised, because they compete with native plants and typically do not support native animals.Eucalyptus has historically been planted to replace California'scoast live oak population, and the newEucalyptus is not as hospitable to native flora and fauna as the oaks. In appropriately foggy conditions on the California Coast,Eucalyptus can spread at a rapid rate. The absence of natural inhibitors such as thekoala or pathogens native to Australia have aided in the spread of CaliforniaEucalyptus trees. This is not as big of an issue further inland, but on the coast invasive eucalypts can disrupt native ecosystems.Eucalyptus may have adverse effects on local streams due to their chemical composition, and their dominance threatens species that rely on native trees. Nevertheless, some native species have been known to adapt to theEucalyptus trees. Notable examples areherons,great horned owl, and themonarch butterfly usingEucalyptus groves as habitat. Despite these successes, eucalypts generally has a net negative impact on the overall balance of the native ecosystem.[80]
A heavy concern regarding Eucalypts in California is their status as a fire hazard.[81]Eucalyptus trees were a catalyst for the spread of the1923 fire in Berkeley, which destroyed 568 homes.[80] The 1991Oakland Hills firestorm, which caused US$1.5 billion in damage, destroyed almost 3,000 homes, and killed 25 people, was partly fueled by large numbers of eucalypts close to the houses.[82]
Despite these issues, there are calls to preserve theEucalyptus plants in California. Advocates for the tree claim its fire risk has been overstated. Some even claim that theEucalyptus's absorption of moisture makes it a barrier against fire. These experts believe that the herbicides used to remove theEucalyptus would negatively impact the ecosystem, and the loss of the trees would release carbon into the atmosphere unnecessarily. There is also an aesthetic argument for keeping theEucalyptus; the trees are viewed by many as an attractive and iconic part of the California landscape. Many say that although the tree is not native, it has been in California long enough to become an essential part of the ecosystem and therefore should not be attacked as invasive. These arguments have caused experts and citizens in California, especially in theSan Francisco Bay Area, to debate the merits ofEucalyptus removal versus preservation. However, the general consensus remains that some areas urgently requireEucalyptus management to stave off potential fire hazards.[83]
Efforts to remove some of California'sEucalyptus trees have been met with a mixed reaction from the public, and there have been protests against removal.[83] RemovingEucalyptus trees can be expensive and often requires machinery or the use of herbicides. The trees struggle to reproduce on their own outside of the foggy regions of Coastal California, and therefore some inlandEucalyptus forests are predicted to die out naturally.[84] In some parts of California, eucalypt plantations 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.[85]
It was introduced in Argentina around 1870 by PresidentDomingo F. Sarmiento, who had brought the seeds from Australia and it quickly became very popular. The most widely planted species wereE. globulus,E. viminalis andE. rostrata. Currently, theHumid Pampas region has small forests andEucalyptus barriers, some up to 80 years old, about 50 meters high and a maximum of one meter in diameter.[86]
Uruguay
Antonio Lussich introducedEucalyptus intoUruguay in approximately 1896, throughout what is nowMaldonado Department, and it has spread all over the south-eastern and eastern coast. There had been no trees in the area because it consisted of dry sand dunes and stones. Lussich also introduced many other trees, particularlyAcacia andpines, but they have not expanded so extensively.[citation needed]
Uruguayan forestry crops usingEucalyptus species have been promoted since 1989, when the new National Forestry Law established that 20% of the national territory would be dedicated to forestry. As the main landscape of Uruguay is grassland (140,000 km2, 87% of the national territory), most of the forestry plantations would be established in prairie regions.[87][88][89]The planting ofEucalyptus sp. has been criticised because of concerns that soil would be degraded bynutrient depletion and other biological changes.[88][89][90] During the last ten years, in the northwestern regions of Uruguay theEucalyptus sp. plantations have reached annual forestation rates of 300%. That zone has a potential forested area of 1 million hectares, approximately 29% of the national territory dedicated to forestry, of which approximately 800,000 hectares are currently forested by monoculture ofEucalyptus spp.[91] It is expected that the radical and durable substitution of vegetation cover leads to changes in the quantity and quality ofsoil organic matter. Such changes may also influencesoil fertility and soil physical and chemical properties. Thesoil quality effects associated withEucalyptus sp. plantations could have adverse effects on soil chemistry;[90][92][93] for example: soil acidification,[94][95][96] iron leaching,allelopathic activities[95] and a high C:N ratio of litter.[92][97][98][99] Additionally, as most scientific understanding of land cover change effects is related to ecosystems where forests were replaced by grasslands or crops, or grassland was replaced by crops, the environmental effects of the current Uruguayan land cover changes are not well understood.[100] The first scientific publication on soil studies in western zone tree plantations (focused on pulp production) appeared in 2004 and described soil acidification andsoil carbon changes,[101] similar to apodzolisation process, and destruction of clay (illite-like minerals), which is the main reservoir of potassium in the soil.[102] Although these studies were carried out in an important zone for forest cultivation, they cannot define the current situation in the rest of the land area under eucalyptus cultivation. Moreover, recently Jackson and Jobbagy have proposed another adverse environmental impact that may result fromEucalyptus culture on prairie soils—stream acidification.[103]
TheEucalyptus species most planted areE. grandis,E. globulus andE. dunnii; they are used mainly for pulp mills. Approximately 80,000 ha ofE. grandis situated in the departments of Rivera, Tacuarembó and Paysandú is primarily earmarked for the solid wood market, although a portion of it is used for sawlogs and plywood. The current area under commercial forest plantation is 6% of the total. The main uses of the wood produced are elemental chlorine free pulp mill production (forcellulose andpaper),sawlogs,plywood andbioenergy (thermoelectric generation). Most of the products obtained fromsawmills andpulp mills, as well as plywood andlogs, are exported. This has raised the income of this sector with respect to traditional products from other sectors. Uruguayan forestry plantations have rates of growth of 30 cubic metres per hectare per year and commercial harvesting occurs after nine years.[citation needed]
Eucalypts were introduced toBrazil in 1910, fortimber substitution and thecharcoal industry. It has thrived in the local environment, and today there are around 7 million hectares planted. The wood is highly valued by the charcoal and pulp and paper industries. The short rotation allows a larger wood production and supplies wood for several other activities, helping to preserve the native forests from logging. When well managed, the plantation soils can sustain endless replanting.Eucalyptus plantings are also used aswind breaks. Brazil's plantations have world-record rates of growth, typically over 40 cubic metres per hectare per year,[104] and commercial harvesting occurs after years 5. Due to continual development and governmental funding, year-on-year growth is consistently being improved.Eucalyptus can produce up to 100 cubic metres per hectare per year. Brazil has become the top exporter and producer ofEucalyptus round wood and pulp, and has played an important role in developing the Australian market through the country's[clarification needed] committed research in this area.
Modern management systems for Eucalyptus plantations often involve careful selection of initial spacing and thinning regimes, which can significantly influence both wood yield and quality.[105] Innovative approaches, such as coppice-with-standards silvicultural systems, have also been reviewed and implemented to optimize biomass production while maintaining sustainability and flexibility in wood uses.[106] Pruning practices in Eucalyptus grandis × Eucalyptus urophylla plantations have been shown to affect growth dynamics and wood quality, supporting their use in high-value timber, pulp, energy, and other wood-based products.[107] The novelty of these management strategies lies in their adaptability to local conditions and market requirements, allowing for the production of wood suited for a range of uses, including bioenergy, construction, and industrial applications.
At the same time, local iron producers in Brazil rely heavily on sustainably grownEucalyptus forcharcoal; this has greatly pushed up the price of charcoal in recent years. The plantations are generally owned and operated for national and international industry by timber asset companies such asThomson Forestry, Greenwood Management or cellulose producers such asAracruz Cellulose andStora Enso.[citation needed]
Overall, South America was expected to produce 55% of the world'sEucalyptus round-wood by 2010. Many environmental NGOs have criticised the use of exotic tree species for forestry in Latin America.[108]
In the East of Angola, theBenguela railway company created eucalyptus plantations for firing its steam locomotives.[citation needed]
Ethiopia
Eucalypts were introduced toEthiopia in either 1894 or 1895, either by EmperorMenelik II's French advisorMondon-Vidailhet or by the Englishman Captain O'Brian. Menelik II endorsed its planting around his new capital city ofAddis Ababa because of the massivedeforestation around the city forfirewood. According to Richard R.K. Pankhurst, "The great advantage of the eucalypts was that they were 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".[109] Plantations of eucalypts spread from the capital to other growing urban centres such asDebre Marqos. Pankhurst reports that the most common species found in Addis Ababa in the mid-1960s wasE. globulus, although he also foundE. melliodora andE. rostrata in significant numbers. David Buxton, writing of central Ethiopia in the mid-1940s, observed that eucalyptus trees "have become an integral -- and a pleasing -- element in theShoan landscape and has largely displaced the slow-growing native 'cedar' (Juniperus procera)."[110]
It was commonly believed that the thirst of theEucalyptus "tended to dry up rivers and wells", creating such opposition to the species that in 1913 a proclamation was issued ordering a partial destruction of all standing trees, and their replacement withmulberry trees. Pankhurst reports, "The proclamation however remained a dead letter; there is no evidence of eucalypts being uprooted, still less of mulberry trees being planted."[111] Eucalypts remain a defining feature of Addis Ababa.
Madagascar
Much of Madagascar's original native forest has been replaced withEucalyptus, threatening biodiversity by isolating remaining natural areas such asAndasibe-Mantadia National Park.[citation needed]
South Africa
NumerousEucalyptus species have been introduced intoSouth Africa, mainly fortimber andfirewood but also for ornamental purposes. They are popular withbeekeepers for thehoney they provide.[112] However, in South Africa they are considered invasive, with their water-sucking capabilities threatening water supplies. They also release a chemical into the surrounding soil which kills native competitors.[61]
As in South Africa, manyEucalyptus species have been introduced intoZimbabwe, mainly for timber and firewood, andE. robusta andE. tereticornis have been recorded as having become naturalised there.[112]
Eucalypts have been grown in Portugal since the mid 19th century, the first thought to be a specimen ofE. obliqua introduced toVila Nova de Gaia in 1829.[113] First as an ornamental but soon after inplantations, these eucalypts are prized due to their long and upright trunks, rapid growth and the ability to regrow after cutting. These plantations now occupy around 800,000 hectares, 10% of the country's total land area, 90% of the trees beingE. globulus. As of the late 20th century, there were an estimated 120 species ofEucalyptus in Portugal.[114] The genus has also been subject to various controversies. Despite representing a large part of the agricultural economy, eucalypt plantations have a negative impact on soil destruction, inducing resistance to water infiltration and increasing the risks of erosion and soil loss, they are highly flammable, aggravating the risk for wildfires. Various Portuguese laws on eucalypt plantations have been formed and reformed to better suit both sides.[115]
There are variousEucalyptus species of public interest in Portugal, namely aKarri inCoimbra's Mata Nacional de Vale de Canas, considered to be Europe's tallest tree at 72 m (236 ft) high.[116][117]
InItaly, theEucalyptus only arrived at the turn of the 19th century and large scale plantations were started at the beginning of the 20th century with the aim of drying up swampy ground to defeat malaria.[118] During the 1930s,Benito Mussolini had thousands ofEucalyptus planted in the marshes around Rome.[119] This, their rapid growth in the Italian climate and excellent function as windbreaks, has made them a common sight in the south of the country, including the islands ofSardinia andSicily.[120] They are also valued for the characteristic smelling and tastinghoney that is produced from them.[121] The variety ofEucalyptus most commonly found in Italy isE. camaldulensis.[122]
InGreece, eucalypts are widely found, especially in southern Greece andCrete. They are cultivated and used for various purposes, including as an ingredient in pharmaceutical products (e.g., creams, elixirs and sprays) and for leather production. They were imported in 1862 by botanist Theodoros Georgios Orphanides. The principal species isE. globulus.[123]
Eucalyptus seeds of the speciesE. globulus were imported intoPalestine in the 1860s, but did not acclimatise well.[125] Later,E. camaldulensis was introduced more successfully and it is still a very common tree inIsrael.[125] The use ofEucalyptus trees to drain swampy land was a common practice in the late nineteenth and early twentieth centuries.[125][126] The German Templer colony ofSarona had begun plantingEucalyptus for this purpose by 1874, though it is not known where the seeds came from.[127] Many Zionist colonies also adopted the practice in the following years under the guidance of theMikveh Israel Agricultural School.[125][126]Eucalyptus trees are now considered aninvasive species in the region.
In India, theInstitute of Forest Genetics and Tree Breeding, Coimbatore started aEucalyptus breeding program in the 1990s. The organisation released four varieties of conventionally bred, high yielding and genetically improved clones for commercial and research interests in 2010.[128][129][130]
Eucalyptus trees were introduced toSri Lanka in the late 19th century bytea andcoffee planters, for wind protection, shade and fuel. Forestry replanting ofEucalyptus began in the 1930s in deforested mountain areas, and currently there are about 10 species present in the island. They account for 20% of major reforestation plantings. They providerailway sleepers,utility poles, sawntimber andfuelwood, but are controversial because of their adverse effect on biodiversity, hydrology and soil fertility. They are associated with another invasive species, theeucalyptus gall wasp,Leptocybe invasa.[131][132]
InHawaii, some 90 species ofEucalyptus have been introduced to the islands, where they have displaced some native species due to their higher maximum height, fast growth and lower water needs. Particularly noticeable is the rainbow eucalyptus (Eucalyptus deglupta), native to Indonesia and the Philippines, whose bark falls off to reveal a trunk that can be green, red, orange, yellow, pink and purple.[133]
Due to similar favourable climatic conditions,Eucalyptus plantations have often replacedoak woodlands, for example in California, Spain and Portugal. The resulting monocultures have raised concerns about loss of biological diversity, through loss ofacorns thatmammals and birds feed on, absence of hollows that in oak trees provide shelter and nesting sites for birds and small mammals and for bee colonies, as well as lack of downed trees in managed plantations. A study of the relationship between birds andEucalyptus in the San Francisco Bay Area found that bird diversity was similar in native forest versusEucalyptus forest, but the species were different.[134] One way in which the avifauna (local assortment of bird species) changes is that cavity-nesting birds including woodpeckers, owls, chickadees, wood ducks, etc. aredepauperate inEucalyptus groves because the decay-resistant wood of these trees prevents cavity formation by decay or excavation. Also, those bird species that glean insects from foliage, such as warblers and vireos, experience population declines whenEucalyptus groves replace oak forest.[citation needed]
Birds that thrive inEucalyptus groves in California tend to prefer tall vertical habitat. These avian species include herons and egrets, which also nest in redwoods.[135][136] ThePoint Reyes Bird Observatory observes that sometimes short-billed birds like theruby-crowned kinglet are found dead beneathEucalyptus trees with their nostrils clogged with pitch.[51]
Monarch butterflies useEucalyptus in California for overwintering, but in some locations have a preference forMonterey pines.[51]
Eucalyptus trees are considered invasive to local ecosystems and negatively impact water resources in countries where they are introduced.[61]
South Africa
In South Africa,Eucalyptus tree speciesE. camaldulensis,E. cladocalyx,E. conferruminata,E. diversicolor,E. grandis andE. tereticornis are listed as Category 1b invaders in theNational Environmental Management: Biodiversity Act. This means most activities with regards to the species are prohibited (such as importing, propagating, translocating or trading) and it should be ensured that it does not spread beyond a plantation's domain.[137]
E. cladocalyx andE. diversicolor are consideredFynbos invaders,[138] and use up to 20% more water than the native fynbos vegetation; with invasive species includingEucalyptus being cleared that reduce Cape Town's water resource by 55 billion litres or two months worth of water supply.[139][140]
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