Eucalyptus alba (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Carbohydrate / starch|
Eucalyptus alba Reinw. ex Blume
- Protologue: Bijdr. Fl. Ned. Ind. 17: 1101 (1827).
- Family: Myrtaceae
- Chromosome number: 2n = 22
- Eucalyptus leucadendron Reinw. ex. de Vriese (1856).
White gum, poplar gum, khaki gum, Timor white gum (En).
Origin and geographic distribution
Eucalyptus alba is native to northern Australia, Papua New Guinea and Timor, and has been planted throughout the tropics. Its present distribution in tropical Africa is unclear, particularly because Eucalyptus alba hybridizes readily with other Eucalyptus species. In Congo, for instance, hybrids of Eucalyptus alba and other Eucalyptus species have been widely used in reforestation. Eucalypts introduced as Eucalyptus alba into Brazil around 1920 in fact belonged to Eucalyptus urophylla S.T.Blake. Large stands of descendants of these trees still exist in Brazil, and are still referred to as Eucalyptus alba. As genuine Eucalyptus alba is also grown in Brazil, there is much confusion.
Eucalyptus alba is mainly used for paper making. The timber is used for light and heavy construction, flooring, mine timber, boat building, furniture, handles, sporting goods, agricultural implements, joinery, railway sleepers, poles and carvings. The wood is often used as fuelwood and for making charcoal. Eucalyptus alba is a bee forage and is used in reforestation programmes and in swampy areas for reclamation purposes. It is also planted as an ornamental tree.
Eucalyptus alba wood from India contained 60.3% holocellulose (including 14.1% pentosan), 27.9% lignin and 0.4% ash. The fibre cells were on average 0.88 mm long and 19.2 μm wide, with a cell wall thickness of 4.8 μm and a lumen width of 9.8 μm. Pulping with the kraft process yielded 49% pulp with good strength properties and low kappa number.
The sapwood is pale reddish brown, the heartwood is darker. The density of the wood is 900–1010 kg/m³ at 12% moisture content. The rates of shrinkage from green to 12% moisture content are 2.9% radial and 4.6% tangential. The wood is moderately strong and hard. The durability ranges from poor to good, depending on provenance and location. The bark contains 30–32% tannins.
Air-dried leaves from Burkina Faso yielded 1.2% oil, with as main compounds β-pinene (31.0%), α-pinene (20.1%), limonene (16.8%), β-caryophyllene (6.6%), γ-terpinene (5.6%), p-cymene (3.2%), α-terpineol (3.1%) and bicyclogermacrene (2.0%). Fresh leaves from Nigeria yielded 0.28% essential oil. The major compounds were α-thujene (32.9%), 1,8-cineole (13.3%), p-cymene (12.9%), β -caryophyllene (7.8%), α-terpineol (2.6%), spathulenol (2.2%) and caryophyllenoxide (1.9%). The oil showed activity against the bacteria Escherichia coli and Pseudomonas aeruginosa, but not against the bacteria Bacillus cereus and Staphylococcus aureus and the fungus Candida albicans. Fresh leaves from DR Congo yielded 0.22% essential oil, with as main compounds β-pinene (25.3%), β-terpineol (13.6%), p-cymene (7.4%), α-terpineol (6.2%), 1,8-cineole (5.2%), limonene (4.6%), β-eudesmol (4.6%), α-pinene (4.3%), β-caryophyllene (4.3%) and spathulenol (4.1%). This oil showed activity against a range of bacteria and fungi.
More or less deciduous, small to large tree up to 25(–40) m tall; bole often of poor form, up to 60(–80) cm in diameter; bark smooth, pink-red to white or cream, surface covered with powdery bloom, exfoliating. Leaves alternate, simple and entire; stipules absent; petiole flattened or angular, 10–33 mm long; blade lanceolate or ovate, 7–21 cm × 2–5 cm, acuminate at apex, thin, green, concolorous, lateral veins conspicuous. Inflorescence axillary, simple; umbels 3–7-flowered; peduncle terete or angular, up to 2 cm long. Flowers bisexual, regular; pedicel absent or angular, up to 7 mm long; flower buds globular to ovoid, 8–9 mm long, divided into a hemispherical hypanthium (lower part), 3–5 mm × 4–7 mm, and a hemispherical operculum (upper part), 3–5 mm × 4–7 mm, which is shed at anthesis; stamens numerous; ovary inferior. Fruit a hemispherical to obconical capsule 4–7 mm × 5–8 mm, opening with 3–4 exserted valves, many-seeded. Seedling with epigeal germination.
On good sites an annual height growth of 3 m is possible during the first years. In Vietnam, for instance, trees in 5-year-old stands were 15 m tall, with an average bole diameter of 17 cm. In trials in Madagascar (Mangoro area, altitude 950 m, average annual rainfall 1200 mm), however, 10-year-old Eucalyptus alba trees, planted at 3 m × 3 m, were only 6.6 m tall, with a basal area of 72 cm² and a total wood production of 33 m³/ha.
Eucalyptus comprises about 800 species, endemic to Australia, except for about 10 species in the eastern part of South-East Asia. Many Eucalyptus species are cultivated outside their natural distribution area, in tropical, subtropical and temperate regions, because of their rapid growth and adaptation to a wide range of ecological conditions. Eucalyptus is divided into several subgenera (7–10, depending on the author), which are subdivided into many sections and series. 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. Eucalyptus species hybridize easily, which adds to the taxonomic complexity.
Around Pointe Noire (Congo) large areas have been planted with clones of the hybrid E. PF1 (clones 1–41), which resulted from natural crosses between 2 or 3 individuals of Eucalyptus alba (mother tree) and a group of poorly identified hybrids from Brazil (father tree). The average productivity of 7-year-old plantations of this hybrid in Congo was 20 m³/ha/year.
Eucalyptus alba is well adapted to dry lowland climates. It grows in areas with an average annual rainfall of (600–)750–2000(–2500) mm, with a dry period of (2–)4–8 months, and a mean annual temperature of 21–30°C, a mean temperature of the warmest month of 32–35°C, and a mean temperature of the coldest month of 5–10°C. It is fairly tolerant of flooding. In its native area Eucalyptus alba grows in flat and undulating country, often near the coast or near watercourses, on heavy soil in woodland and open forest from sea level to 700 m altitude.
Eucalyptus alba is easily propagated by seed. The 1000-seed weight is 1.1–3.7 g. One gram of dry seeds produces 100–250 seedlings. Grafting is easy, but propagation by cuttings gives more problems. For pulpwood a spacing of 3 m × 2 m is common. Eucalyptus alba has a good coppicing ability. The main diseases in Eucalyptus alba plantations, particularly in Brazil, are caused by Cylindrocladium fungi. In Brazil rotations of 5–7 years are used for pulpwood production, and rotations of 15–30 year for timber. On sandy and clayey savanna soils in the Congo basin mean annual volume increments of 6–10 m³/ha have been recorded.
Substantial genetic variation is present within Eucalyptus alba, and careful progeny testing should be carried out when it is considered for planting.
Eucalyptus alba is a useful source of pulpwood, timber and fuel in the dry lowland tropics. Its distribution, importance and prospects for tropical Africa are difficult to assess, especially because it hybridizes readily with other Eucalyptus species.
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- S. Masila, P.O. Box 102977-00101, Nairobi, Kenya
Correct citation of this article
Masila, S., 2011. Eucalyptus alba Reinw. ex Blume. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 14 November 2020.
- See the Prota4U database.