Eucalyptus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Eucalyptus L'Hér.

Protologue: Sert. angl. 18 (1788), t. 20 (1792).

Family: Myrtaceae

Chromosome number: x= 11; 2n= 22 for the vast majority of species, E. citriodora: 2n= 20, 22, 28, 44

Trade groups

Eucalypt: lightweight to medium-weight or heavy hardwood, e.g. Eucalyptus alba Reinw. ex Blume, E. deglupta Blume, E. urophylla S.T. Blake.

Vernacular names

Eucalypt

• eucalyptus (Fr)
• Indonesia: ampupu, leda
• Papua New Guinea: kamerere
• Philippines: bagras
• Thailand: yukhalip (general)
• Vietnam: bạch dàn dỏ.

Origin and geographic distribution

Eucalyptus is a genus of over 500 species, most of them endemic to Australia. Only 2 species are confined to the Malesian area (New Guinea, the Moluccas, Sulawesi, the Lesser Sunda Islands and the Philippines). Several species extend from northern Australia towards eastern Malesia. At present over 10 species are known from the southern region of New Guinea. As botanical exploration of the savanna and monsoon forests of this region continues, the number of species encountered here is expected to increase. The largest diversity is in the coastal regions of New South Wales and in south-western Australia. At present, many species are being cultivated outside their natural distribution area, for example in the Malesian area but also in continental Asia, tropical and subtropical Africa, southern Europe and South and Central America.

Uses

The wood of eucalypt is used as a general-purpose timber. It is suitable for light or heavy construction. In house building its applications are for doors, window frames, interior finish and both light and heavy duty flooring. Because of its moderate durability and moderate resistance to insect attacks the timber is also applied in contact with the ground, in railway sleepers, poles and posts. Other applications are in ship and boat building, vehicle bodies, joinery, boxes and crates, vats, carving, turnery, handles, sporting goods and agricultural implements. The timber is suitable for the production of veneer and plywood, particle board, hardboard and wood-wool boards. One of the major uses of eucalypt is the production of pulp for paper manufacture. Eucalypt is also a very important supplier of firewood, which generally burns very quickly because of the high oil content, while many produce a good-quality charcoal. Several species are being used in reforestation projects.

The leaves and twigs of many Eucalyptus species contain eucalypt oil which is an important product for pharmaceuticals (for example as a liniment or cough medication), perfumes, and soaps and detergents. The oil is also used as a disinfectant and pesticide. Many species of Eucalyptus produce gum (kino), which often runs down the bole in large quantities. The bark of some species has tanning properties. The flowers of many species produce good pollen and nectar for honey. Some species are planted as ornamentals.

Production and international trade

Little information is available on production and trade of eucalypt timber and pulp. However, eucalypt is becoming increasingly important, as it is nowadays used on a large scale for reforestation. In Papua New Guinea E. deglupta is one of the major export timbers; it is ranked in the MEP (Minimum Export Prices) group 3 and fetched a minimum export price for saw logs of US$ 50/m³ in 1992. In Thailand the export of eucalypt chips and particles in 1989 was 28.6 million kg (with a value of US$ 2.4 million) and in 1990 52.2 million kg (with a value of US$ 5.8 million). The export of eucalypt wood of small dimensions (to be used for implements, sticks, etc.) in Thailand in 1989 was 73.7 million kg (with a value of US$ 3.4 million) and in 1990 40.6 million kg (with a value of US$ 1.8 million). The export is mainly to Japan and Taiwan.

Properties

Eucalypt wood is light, medium-weight or heavy. The heartwood is light brown to reddish-brown, sometimes dark reddish-brown on exposure, the sapwood is white, cream or light pinkish, 20-60 mm thick and more or less distinctly demarcated from the heartwood. The density of the wood varies greatly between species and also between provenances of a single species (e.g. planted or natural-growing, young or old trees); at 12% moisture content it may be as low as 400 kg/m³ for plantation-grown E. deglupta (trees of 11-13 years old) to as high as 800 kg/m³ for E. deglupta trees of natural stands, 980 kg/m³ for E. camaldulensis and even 1010 kg/m³ for E. alba. The grain is straight to interlocked, texture moderately coarse to coarse. A ribbon figure is often present on quarter-sawn surfaces.

At 12% moisture content the modulus of rupture is (50-)67-142 N/mm², modulus of elasticity 8000-18 800 N/mm², compression parallel to grain 39-76 N/mm², shear 7-17 N/mm², cleavage 59-89 N/mm radial and 56-98 N/mm tangential, Janka side hardness 5030-10 100 N and Janka end hardness 5870-10 410 N.

The rates of shrinkage are moderate to high, from green to 12% moisture content 1.8-3.0(-4.4)% radial and 3.4-7.0(-8.9)% tangential. Care is needed during seasoning, especially with the heavier timber, as backsawn boards tend to check; close spacing of stacking strips is important. Kiln drying of heavier grades of eucalypt timber is only practicable in boards up to 25 mm in thickness. It is strongly recommended to air dry the wood to 30% moisture content prior to kiln drying. Boards of E. deglupta wood of 25 mm thick will require about 4 months air drying and 3 days kiln drying, boards of 50 mm thick about 6 months air drying and 4 days kiln drying.

Wood of E. deglupta works well with hand and machine tools, although it has a slight tendency to tear out in machining and boring and to slight chipping of sharp edges in turning. Heavier grades of timber are rather difficult to work with hand tools, and sharp edges are required in planing to prevent picking up. With care a smooth finish can be obtained. Eucalypt wood glues well, but pre-boring is advisable for screwing and nailing to prevent end splitting. It stains and paints well. It slices well if the wood has a high moisture content, and the veneer often has an attractive figure; the veneer dries satisfactorily. Kraft pulping of E. deglupta wood gives a yield of 50%, and a pulp of good brightness and satisfactory handsheet strength properties.

The durability may differ considerably; natural rain forest material is rated as moderately durable to durable, but plantation material is non-durable. Growth site and provenance may also affect durability. Wood of E. deglupta is liable to termite and Lyctus attack (particularly sapwood), and also to marine borers. The heartwood is usually resistant to preservative treatment and the sapwood permeable, but in plantation-grown material the uptake of copper-chrome-arsenate salts may be fair; plantation-grown wood of E. deglupta is significantly easier to impregnate than wood from natural forest.

The wood is non-siliceous, tasteless and odourless. Wood of E. deglupta contains 51% cellulose, 30% lignin, 14.5% pentosan and 1.2% ash. The energy value of eucalypt wood is 18 500-21 100 kJ/kg.

The chief constituent of Eucalyptus oil is eucalyptol. The oil has a camphor-like odour and a spicy, cooling taste. It is practically insoluble in water, but miscible with alcohol, chloroform, ether, glacial acetic acid and oils.

Description

• Small to very large trees of up to 60(-87) m tall; bole generally well-shaped, up to more than 200 cm in diameter; bark surface smooth, fibrous, stringy or tessellated.
• Plant heterophyllous, i.e. with juvenile and adult phases occurring in most species; adult leaves generally alternate but sometimes opposite, simple, pendulous, rarely erect, lanceolate, often falcate, with a distinct midrib, pinnately veined or with parallel veins, aromatic when crushed, glabrous.
• Inflorescence an umbelliform condensed and reduced dichasium usually called a conflorescence, pedunculate, solitary or paired in a leaf axil, or in a terminal sometimes corymbose panicle; 3 or more flowers per umbel, rarely only one.
• Flowers regular, bisexual or sometimes male, bud clearly divided into calyx tube or hypanthium (lower part) and operculum (upper part); sepals and petals forming an outer and inner operculum respectively or sepals and petals adnate and forming a single operculum that is shed at anthesis, sepals rarely free; stamens numerous, usually on a staminophore, outer stamens fertile or sterile; ovary 3-7-locular, inferior or partly superior, with many ovules.
• Fruit a dry thin-walled capsule enclosed in a woody hypanthium, opening with valves, rarely circumscissile, with scars of operculum and staminophore at the rim.
• Seeds several to many, brown, grey or black.
• Seedling with epigeal germination; cotyledons equal, bisected, bilobed or reniform, often broader than long; first pairs of leaves decussate on a square stem.

Wood anatomy

• Macroscopic characters:

• Heartwood varying from light to dark reddish-brown except in E. citriodora where it is light brown to grey-brown and sometimes waxy to the touch; sapwood whitish, pinkish or cream, usually 25-60 mm wide but width varying with growth rate.
• Grain straight to interlocked, forming a ribbon stripe when quarter-sawn, fiddleback figure sometimes evident in E. citriodora.
• Texture rather coarse with a slight lustre in E. deglupta. Growth rings apparent in E. camaldulensis, but not distinct in other species; vessel lines always conspicuous, longitudinal surface of E. citriodora with very conspicuous vessel lines. Kino veins (gum veins) are a prominent feature of the genus.

• Microscopic characters:

• Growth rings generally indistinct, sometimes evident in E. camaldulensis, having some thick-walled latewood cells.
• Vessels diffuse, (4-)7-9(-11)/mm², predominantly solitary in E. camaldulensis and E. deglupta, in short to long radial multiples of up to 4(-5), sometimes with clusters in E. alba and E. citriodora, variable in size, (90-)160-190(-240) µm, particularly large in E. deglupta (190(-240) µm), oblique arrangement prominent but less marked in E. alba; perforation plates exclusively simple; intervessel pits alternate, 7-12 µm; vessel-ray pits with reduced borders to almost simple, round to oval, 10-12 µm; tyloses moderately abundant to very abundant.
• Vasicentric tracheids usually abundant.
• Fibres (800-)1000-1300(-1400) µm long, 14-16(-18) µm in diameter, non-septate, thin- to thick-walled, with conspicuously bordered pits mainly on radial walls.
• Parenchyma moderately abundant to abundant, paratracheal and apotracheal types present, diffuse and vasicentric parenchyma present in all species, aliform to confluent in E. citriodora (may include sporadic, narrow wavy bands), tending to aliform around smaller pores of E. alba, strand length 4-8 cells.
• Rays (7-)10-14(-16)/mm, 1-3-seriate, (13-)16-21(-26) cells high, homogeneous to weakly heterogeneous with one to several rows of procumbent cells on ray margins with greater vertical dimensions than the central procumbent cells.
• Chambered crystal strands very prominent in E. deglupta and sometimes present in E. citriodora ; silica bodies absent.
• Traumatic axial gum canals (known as "kino veins") frequently present in all species.

Species studied: E. alba, E. camaldulensis, E. citriodora, E. deglupta.

Eucalyptus can be divided into two distinct groups based on the presence or absence of vessel multiples and axial parenchyma. The first group, comprising E. alba and E. citriodora, possesses vessel multiples, paratracheal and apotracheal parenchyma, abundant in E. citriodora; species in the second group, comprising E. camaldulensis and E. 'deglupta, have predominantly solitary pores and fewer parenchyma.

Growth and development

Seeds of E. deglupta have a germination rate of 50-60% and one gram of dry seeds produces 1000-2000 seedlings. Shoot growth of young trees appears to be continuous, provided soil moisture is adequate. Young trees have a conical crown with a definite leader and almost horizontal branches. As the tree ages, branches curve up at the ends and the leader becomes less dominant. In time the tree acquires a spreading, flat-topped crown. The average annual volume increment of E. deglupta in plantations is 15 m³/ha but is occasionally as much as 50 m³/ha. At the age of 25 years the trees reach an average height of 42 m and an average bole diameter of 40 cm. E. urophylla is also a fast grower; at the age of 8 years the trees have an average height of 27 m and an average diameter of 23 cm, the average annual volume increment being 20-30 m³/ha. E. platyphylla grows more slowly; the average height of trees in plantations in Java is only 13 m at 7 years old (average diameter 13.5 cm).

In E. deglupta flowering may occur within the first year but more often it takes place after 2 years and annually thereafter. Flowering can occur in all months of the year depending on locality. In New Britain seeds are shed between December and April which are the wetter months of the year. In Indonesia E. deglupta flowers during the whole year and bears fruits at the beginning of the rainy season. E. urophylla flowers during the rainy season.

In New Britain it has been noted that seeds of E. deglupta are often dispersed by river. The flooding rivers in the wet season deposit the seeds mixed with humus on uncolonized alluvium in full sunlight; this constitutes ideal conditions for germination.

Other botanical information

The large genus Eucalyptus belongs to the group of "capsular-fruited" Myrtaceae and is divided into several (7 to 10 depending on the author) subgenera which are in turn divided into many sections and series. Its closest relative is probably the genus Angophora but others, like the New Caledonian genus Arillastrum and Eucalyptopsis, are also closely related to Eucalyptus. The results of phylogenetic studies within Eucalyptus suggest that the genus is polyphyletic, hence not of a single evolutionary origin, and consequently it has been proposed to divide the genus into several distinct genera. This has not yet been done, mainly because of the nomenclatural whirlpool this would bring about.

Several species which are not treated under the selection of species have gained interest as plantation trees recently in South-East Asia, e.g. E. exserta F. v. Mueller and E. pellita F. v. Mueller.

Ecology

Almost all species of Eucalyptus are adapted to a monsoon climate. Many species can even survive a severe dry season, e.g. the cultivated species E. alba, E. camaldulensis, and E. citriodora. E. deglupta is the only species of Eucalyptus which is adapted to lowland and lower montane rain forest habitats. It does not grow naturally in areas with a pronounced dry season, but it occurs in areas where the annual rainfall is 2500-5000 mm and the monthly rainfall usually exceeds 150 mm. Because of this, E. deglupta is widely planted throughout the wet tropics. It occurs from sea-level up to 1800 m altitude. Monthly temperatures in lowland habitats are 23°C (mean minimum) to 31°C (mean maximum). In highland areas temperatures range from 13°C (mean minimum) to 29°C (mean maximum). E. deglupta may grow in cooler environments but does not tolerate frosts. The species does not withstand prolonged flooding and is highly sensitive to fires. It requires full overhead light for development and dense stands are commonly found along rivers where it has colonized newly formed sand banks. E. deglupta is also found on sites that have been cleared or disturbed in some way, e.g. by landslides, volcanic eruptions, or shifting cultivation. It is a rapid colonizer of such sites. In time, however, other species colonize and form a dense understorey which prevents subsequent E. deglupta regeneration. The other eucalypt species occurring naturally in southern New Guinea are generally found in dry seasonal open forest or savanna-like vegetations on alluvial plains, hills and plateaus, sometimes also on ridges and on loamy and lateritic, sometimes clayey soils.

Propagation and planting

Eucalypts can be propagated easily from seed and sometimes from cuttings. Seeds germinate in 4-20 days. Seedlings are best raised in trays filled with sterile, fine, loamy sand. The trays should be kept in the shade for the first few days after sowing but light can be gradually increased to 50% full sunlight. Seedlings can be transferred to planting tubes when they have 2-3 leaf pairs. Further growth requires full sunlight. The seedlings are ready for planting in the field when they are 25-30 cm in height, usually after 3-4 months. About 2 weeks before planting into the field, they should be gradually hardened off by reducing watering and removing shade. Seeds of many Eucalyptus species can be imported from commercial suppliers in Australia. The weight of 1000 seeds of E. citriodora is 4.5-7.1 g, for E. urophylla it is 2.5-4.8 g, for E. grandis 1.5-1.7 g, for E. camaldulensis 1.3-1.4 g and for E. deglupta 0.3-0.5 g. Hence, the seeds are very light. Eucalypt seeds can be stored for several years when kept dry, cool and airtight. Annual seedling production of eucalypts was approximately 2 million in Thailand in the early 1980s.

Vegetative propagation is possible from branch cuttings, but these must be taken from trees less than 2 years old. Best results are obtained from cuttings containing a stem node and a segment of a leaf. Hormones such as indole-acetic acid, indole-butyric acid or naphthalene-acetic acid will improve the success rate.

Plantations can be established at 3-4 m regular spacings, but spacing of 3 m × 2 m is also practised. In Java stumps are used for planting E. platyphylla with a spacing of 3 m × 1 m. The preferred length of the stem of the stump is 10 cm with a diameter of 0.5-1.5 cm, and the length of the root 20 cm.

Silviculture and management

Good weed control (usually a 1 m strip along each planting line) is essential and 4-5 weedings each year for 2 years may be necessary before site occupancy is achieved. Growth is usually rapid and subsequent management depends on the purpose for which the trees are being grown. If grown for pulpwood, trees can be harvested after 6-10 years. Plantations grown for sawlogs will require thinning. In Papua New Guinea, malformed trees and those with double leaders are removed at 5 years; the stand is then thinned to 250 trees/ha at 10 years, 100 trees/ha at 15 years and the final harvest is at 25 years. E. deglupta does not coppice vigorously and must be replanted. Other species such as E. camaldulensis, E. grandis and E. urophylla do coppice well. E. deglupta has been used in enrichment planting trials in logged-over forest and shows considerable promise. Favourable response to boron and nitrogen fertilizers has been obtained in plantations in Papua New Guinea. Foliar analyses suggest that the critical leaf nitrogen concentration is 2.1% and the optimum nitrogen/phosphorus ratio about 10. In the Philippines 6-7 g of fertilizer is used per seedling 2 months after transplanting. E. camaldulensis in the Philippines responds well to moderate levels of both nitrogen (30 g/plant) and phosphorus (30 g/plant) when applied within 3 months after planting.

Diseases and pests

Heart rot is sometimes found in older trees of E. deglupta but is unlikely to be a problem in trees grown on a short (e.g. 10 years) rotation. Field observations suggest that heart rot is more common in trees growing on less well-drained sites. Eucalypt seedlings are susceptible to damping-off in the nursery. Regular application of a fungicide can control this problem.

Various stem-borers have caused damage in some areas. In Papua New Guinea the most serious of these is the buprestid beetle (Agrilus opulentus). It mainly attacks small suppressed trees and can kill them by girdling the stem. There is strong evidence that susceptibility to Agrilus varies with provenance. In trials in Papua New Guinea E. deglupta originating from Mindanao were most resistant to attack, while trees originating from Sulawesi and the highlands of mainland Papua New Guinea were most susceptible. In Malaysia a cossid moth (Zeuzera coffea) has also caused stem damage. Other pests include the ring bark borer Endoclita hosei and the leaf defoliator Hypomecas squamosus in Malaysia, the termite Nasutitermes novarumhebridarum (in Papua New Guinea) and the coreid bug Amblypelta cocophaga (in the Solomon Islands). Some control of the latter pest has been achieved by introducing the ant Oecophylla smaragdina from Papua New Guinea and by clearing vegetation between the planting lines. Clearing appears to benefit the plantation trees by removing alternative insect host plants. Aphids have occasionally been a problem in eucalypt plantations in Indonesia. Application of dieldrin to the potting medium of seedlings reduces the damage caused by termites to the root system of young plants. In New Britain the giant snail Athatina fulica may cause a loss of up to 40% of unprotected seedlings; a bamboo ring dipped in creosote and placed around each seedling achieves effective control.

Harvesting

Eucalypt plantations are clear-cut when the rotation age has been reached, and subsequently replanted with nursery-raised seedlings. Buttresses, often 3-4 m high, are frequent on specimens of E. deglupta growing on river alluviums and non-stable soils in the natural area of distribution of the species; to harvest the logs, scaffolding has to be built so the stem can be sawn through above the buttresses.

Yield

Mature eucalypt trees may yield much timber. Occasionally the logs of E. deglupta trees in New Britain are branchless for 45 m and have a diameter of 2.3 m, yielding 175 m³ of timber per tree. E. deglupta is one of the fastest growing hardwood trees in the world. In pulpwood plantations yields of 200-300 m³/ha at 10-12 years of age are commonly achieved. High yields can also be obtained from plantations managed for sawlog production. A 20-year-old plantation in New Britain yielded 520 m³/ha from trees 54.5 m tall on average with mean diameter of 49.5 cm at breast height. Yields can be substantially reduced by seasonal drought stress.

Genetic resources

Provenance trials in Papua New Guinea using seed collected across the whole range of E. deglupta show variability in morphology, growth, and susceptibility to pests. Mindanao, Sulawesi and New Britain provenances appear to be better than the mainland Papua New Guinea ones. The trials included most of the mainland Papua New Guinea provenances of E. deglupta but not many from Indonesia or the Philippines. In view of the variability already evident, it is highly desirable that the remaining provenances be tested as soon as possible, especially as some may be threatened by clearing for agriculture.

In other species, there is also substantial provenance variation, e.g. in E. camaldulensis in Australia; some provenances are outstanding for tropical climates, some for alkaline soils, etc. Provenance variation is also considerable in E. grandis (Australia), and E. urophylla (Indonesia).

Prospects

E. deglupta shows great promise for reforestation and afforestation in wet tropical lowland areas without a pronounced dry period. It has particularly high potential for industrial pulp production because of its rapid growth and excellent wood properties. Locally, it is already planted on a large scale, for instance in East Kalimantan. Where heart rot and insect pests have been reported they appear to be only locally significant. Further, because of the genetic variability of E. deglupta and its very short reproduction period, there are good prospects for tree improvement which may help overcome these problems.

Other species are particularly suited for planting in dry areas (e.g. E. camaldulensis) or mountainous areas (e.g. E. urophylla). These species also have great potential for use as firewood in coppice systems.

Literature

• Chew, T.K., 1980. Growth of Eucalyptus species in Peninsular Malaysia. Malaysian Forester 43: 8-15.
• Chippendale, G.M., 1988. Eucalyptus. In: George, A.S. (Editor): Flora of Australia. Vol. 19. Australian Government Publishing Service, Canberra. pp. 1-448.
• Davidson, J., 1973. A description of Eucalyptus deglupta. Tropical Forest Research Notes No 7. Department of Forests, Port Moresby. 23 pp.
• Eldridge, K.G., 1975. Eucalyptus camaldulensis. Tropical Forestry Papers No 8. CSIRO, Division of Forest Research, Canberra. 59 pp.
• Haslett, A.N., 1986. Properties and uses of the timbers of western Samoa. Plantation-grown exotic hardwoods. Ministry of Foreign Affairs, Wellington. pp. 16-17.
• Heather, W.A., 1955. The kamerere forests of New Britain. Empire Forest Review 34: 255-278.
• Jacobs, M.R., 1981. Eucalypts for planting. 2nd Ed. FAO Forestry Series No 11. FAO, Rome. 677 pp.
• Johnson, L.A.S., 1976. Problems of species and genera in Eucalyptus (Myrtaceae). Plant Systematics and Evolution 125: 155-167.
• Suhaendi, H. & Djapilus, A., 1978. Pemilihan jenis-jenis Eucalyptus dalam'usaha reboisasi dan prospek pengembangannya di daerah-daerah [Selection of Eucalyptus species for reforestation work and prospects for growing them in various regions]. Lembaran Pengembangan No 2. Lembaga Penelitian Hutan, Bogor. iv + 40 pp.
• Whitmore, J.L., 1978. Bibliography on Eucalyptus deglupta Bl. Research Note 17, Institute of Tropical Forestry. Forest Service USDA, Rio Piedras. 18 pp.

Selection of species

• Eucalyptus alba
• Eucalyptus camaldulensis
• Eucalyptus citriodora (as Corymbia citriodora
• Eucalyptus deglupta
• Eucalyptus grandis
• Eucalyptus gummifera
• Eucalyptus papuana
• Eucalyptus platyphylla
• Eucalyptus robusta
• Eucalyptus saligna
• Eucalyptus tereticornis
• Eucalyptus torelliana
• Eucalyptus urophylla

Authors

• D. Lamb (general part),
• R.J. Johns (general part),
• W.G. Keating (properties),
• J. Ilic (wood anatomy),
• C.C.H. Jongkind (selection of species)