3011

11: Auxiliary plants

Eucalyptus tereticornis J.E. Smith

Spec. bot. New Holland 1: 41 (1795).

MYRTACEAE

2n = 22

Eucalyptus subulata Cunn. ex Schauer (1843), Eucalyptus insignis Naudin (1891), Eucalyptus umbellata (Gaertner) Domin (1928) non Desf.

Forest red gum, blue gum (En). Cambodia: pré:ng khchâl' slök tô:ch.

Eucalyptus tereticornis has an extensive natural distribution in a long strip about 100 km wide, from southern Papua New Guinea and the northern tip of Queensland to southern Victoria along the east coast of Australia. The Great Dividing Range separates its area of distribution from that of Eucalyptus camaldulensis Dehnh. It was one of the first eucalypts exported from Australia and is now cultivated throughout the tropics, on an especially large scale in India and Brazil.

Eucalyptus tereticornis is used for reforestation, shelter-belts and shade. The wood is a major source of fuelwood, charcoal, and timber for local use. It is hard, strong and durable and is also used for light and heavy construction, railway sleepers, bridges, wharves, piles, poles, mining timber, pulpwood, hardboard and particle board. Eucalyptus tereticornis is a major source of pollen and nectar, producing a caramel-flavoured honey. The leaves are one of the sources of eucalypt oil. The essential oil and the tannin from wood and bark are not utilized commercially.

Eucalyptus tereticornis is among the four most commonly planted Eucalyptus species throughout the world. It is, therefore, most likely that saw and veneer logs and pulp of Eucalyptus tereticornis are internationally marketed, but specific information is lacking. In Vietnam approximately 16 000 ha have been planted, in India over 500 000 ha and in Brazil about 250 000 ha.

The sapwood is grey to cream-coloured and fairly well demarcated from the pale to dark red heartwood, of even texture with wavy or interlocked grain, making it somewhat difficult to finish. At 12% moisture content the density of the wood from plantations is considerably lower (e.g. 730—800 kg/m³, Madagascar) than that from natural forests (910—1010 kg/m³, Australia). The energy value of the wood is 20 000—22 000 kJ/kg. The shrinkage of wood during seasoning is high and it has a strong tendency to warp. In Australia, the wood is one of the most resistant to marine borer attack, but it failed after 2.5—10 years at the Pacific coast of the United States. Sapwood is susceptible to Lyctus. The wood contains 0.5% essential oil and 6—12% tannin; the bark contains 3—15% tannin. The wood yields a very good quality pulp.
Commercial seed contains 320—600 viable seeds per gram. About 90% of commercial seed is chaff consisting mainly of unfertilized ovules.

A large tree, up to 50 m tall, bole straight and clear for more than one-half, up to 2 m in diameter. Bark decorticating over the whole trunk in large plates or flakes to leave a smooth or mat, mottled surface, white, grey or grey-blue; some rough, dead bark is frequently retained at the base of the tree. Leaves alternate, thick; petiole 13—24 mm long, terete or channelled; blade narrowly lanceolate to lanceolate, 10—20 cm x 1—2.7 cm, acuminate, glabrous, shiny green, concolorous with venation conspicuous, pinnate, lateral veins angled at 40—50° to the midrib. Inflorescence an axillary, simple, condensed and reduced, umbelliform dichasium, usually called a conflorescence; umbels solitary, 7—11-flowered; peduncle terete or angular, 7—25 mm long; pedicel 3—10 mm long; flowers regular, bisexual, white; flower buds clearly divided into a calyx tube or hypanthium (lower part), and operculum (upper part, formed by the calyx lobes and petals) which is shed at anthesis; hypanthium hemispherical, 2—3 mm x 4—6 mm; operculum acutely conical, 8—13 mm x 4—6 mm; stamens numerous, on a staminophore, erect and all fertile, anthers versatile, oblong, opening by longitudinal slits; ovary inferior, with many ovules. Fruit a dry, thin-walled capsule enclosed in a woody hypanthium, opening with 4—5 strongly exserted valves, subglobular to ovoid, 5—7 mm x 4—8 mm, with broad, steeply ascending disc. Seed rough, brown-black. Seedling with epigeal germination, at first with square stem; cotyledons bilobed; leaves decussate; juvenile leaves opposite for 2—3 pairs, then alternate, petiolate, ovate, 6—16 cm x 5—6 cm, dull, green to blue-green, slightly discolorous.

In plantations, Eucalyptus tereticornis starts flowering when 2—6 years of age; 2-month-old seedlings have been observed flowering in Brazil. Small clusters of white flowers appear every year, but heavy blooming occurs only once every 3—4 years. In a 3-year-old plantation in Java the mean annual increments in height and in diameter were 4.2 m and 3.5 cm, respectively; in 4-year-old trials in Peninsular Malaysia they were 2.0—3.6 m and 1.7—3.3 cm; in 1-year-old trials in Thailand, 1.7—6.5 m and 2.5—6.8 cm, depending on provenance and site. On a poor site in Papua New Guinea the annual increments were 3.3 m and 2.1 cm. On favourable sites in Indonesia trees attain a height of 35 m in 10 years, on poorer sites 15—18 m. The presence of ectomycorrhizal associations in Eucalyptus tereticornis has been assumed, but has not yet been confirmed.

Eucalyptus tereticornis is closely related to Eucalyptus camaldulensis and natural hybrids are sometimes encountered. Eucalyptus camaldulensis differs by its usually smaller habit, the alternate juvenile leaves, the rostrate to obtusely conical operculum and the smooth seed. Many early introductions of Eucalyptus tereticornis were derived from very few original seed trees. The inbred landrace 12ABL is thought to be descended from a single tree in Madagascar and is widely planted in West Africa; Eucalyptus C is a landrace or possibly a hybrid from Zanzibar and is planted in East Africa. 'Mysore gum', which represents about half of the eucalypt plantations in India, is believed to originate from a few trees in the Nandi Hills (Andhra Pradesh, India). It is also known as 'eucalyptus hybrid' or 'Mysore hybrid', although it is now considered to be mainly Eucalyptus tereticornis, with only occasional evidence of hybridization with Eucalyptus robusta J.E. Smith and probably Eucalyptus camaldulensis.

Eucalyptus tereticornis occurs from 6—38°S latitude and climatic conditions in its natural range vary greatly. Rainfall distribution varies from monsoonal with marked dry and wet seasons in southern Papua New Guinea, a summer rainfall climate with a very dry winter in Queensland, and an even distribution of rainfall in southern Queensland, to a dry summer and cold, wet winter in eastern Victoria. Mean annual rainfall is (500—)800—1500(—3500) mm with a dry season of up to 7 months. Eucalyptus tereticornis is mainly found on alluvial flats in cooler and drier areas, on lower hill-slopes in higher rainfall areas, and on upper slopes and plateaux in the tropics. Its altitudinal range is from near sea level up to 900 m in Australia and up to 1800 m in Papua New Guinea. The mean maximum temperature of the hottest month is 22—32°C, the mean minimum temperature of the coldest month 2—12°C. Up to 15 days of frost are tolerated. In southern China and Pakistan adapted selections are reported to survive —7°C. Soil conditions seem to limit its natural occurrence. It is not found on heavy clay, acid or dry, shallow soil, preferring deep, well-drained, fairly light-textured alluvial soil. Eucalyptus tereticornis can stand occasional flooding and in India, it is highly resistant to waterlogging during the first year, although in natural forest it is rare under such conditions.

Eucalyptus tereticornis can be propagated by seed or cuttings. For transport of seed, it may be worthwhile to separate seed and chaff, e.g. by sieving. Seed can be stored for several years if air-dried and stored in the dark in sealed containers at a temperature of 1—4°C. The germination rate can be maintained at an acceptable level for 1—2 years by storing the seed in unsealed containers at room temperature. The germination rate of Eucalyptus spp. is commonly given as the number of plants obtainable from 1 g of seed (with chaff), e.g. 480 for Eucalyptus tereticornis, corresponding with about 80% germination. The most common and effective way to raise seedlings is to sow the small and untreated seed in trays under light shade in a sterilized medium (e.g. soil or vermiculite). A sowing rate of 10—15 g/m² is recommended, but the sowing density should be decreased in areas with a high risk of damping off. Seed germinates in 4—14 days. The young seedlings are pricked out and transplanted into containers when 2—4 pairs of leaves above the cotyledons have developed. An additional 3—6 months in the nursery is required to obtain seedlings of plantable size. Direct sowing in containers is also practised, but it is very difficult to sow only a few of the minute seeds per container. Watering is done by spraying. Bare-rooted planting stock may be used in areas with a humid climate, while stumps have proved satisfactory in India. Recorded spacings at planting are 2 m x 2 m (East Java), 2.7 m x 3.0 m (Peninsular Malaysia), 1—2 m x 1—2 m (the Philippines) and 2.7 m x 2.7 m (Papua New Guinea). In Papua New Guinea, growth is satisfactory on infertile and poorly drained grassland and on copper mine tailings, provided that N, P and K fertilizer is applied. Vegetative propagation using branch cuttings of 2—3-year-old saplings and from suckers has been successful.

Clean weeding is extremely important for good establishment and early canopy closure. In grasslands with Themeda triandra Forssk. and Imperata cylindrica (L.) Raeuschel in the Philippines, weeding is done every 3—4 months to obtain a seedling survival of 80—100%. For the production of firewood and pulpwood, rotations of 7—12 years are applied. Thinning is done 2—5 years after planting. Eucalyptus tereticornis coppices vigorously and regeneration by coppice is commonly practised. After the original seedling crop, 2—4 coppice crops can be harvested. After cutting, two—several coppice shoots remain after 'self-thinning'. These are thinned to 1—3 coppice shoots per stool at the age of 18 months. For the production of construction wood the rotation is 20—30 years with a final density of 70—120 trees/ha. In Papua New Guinea, ploughing and mounding helps to mineralize sufficient soil nutrients to enable adequate growth. The initial planting density is 1300—1600 trees/ha, reduced to 900 trees/ha after 5 years. Resprouting after fire was observed in the Philippines, but fire killed 80% of the seedlings planted six months earlier.

Eucalyptus tereticornis is fairly free from diseases and pests. Damping-off in the nursery may be a serious problem, but reducing shade and humidity can prevent major damage. In the Solomon Islands, dieback attributed to the coreid bug Amblypelta cocophaga was observed in 3—4-month-old plantings. Resistance to termite attack is generally very high, but Neotermes insularis may attack the tree in its natural distribution area.

When harvested the stool should be lower than 12 cm to allow for the development of stable shoots.

In East Java, the mean annual increment over 10 years is 27 m³/ha for a trial plantation at 800 m altitude. On good sites, 18—25 m³/ha may be generally expected. A mean annual increment of 30—35 m³/ha for the hybrid of Eucalyptus tereticornis x Eucalyptus grandis W. Hill ex Maiden was recorded over 6—7 years on savanna sands in Congo.

Provenances have been conserved ex situ in Congo, Nigeria, Zambia, Fiji and Bangladesh. Seed is commercially available in Australia from a great number of provenances. The 'Mysore hybrid' or 'eucalyptus hybrid', used in most plantations in India, is a complex of landraces of Eucalyptus tereticornis, suspected to have originated from a restricted genetic base of Australian trees, and hybrids with Eucalyptus robusta or Eucalyptus camaldulensis. Performance in plantations has left much to be desired due to the great variability within stands and slow growth compared with pure species of appropriate provenance.

An important effort has been put into progeny and provenance research particularly in the tropical provenances from north-eastern Queensland. Eucalyptus species often hybridize readily. Natural populations with intermediate characteristics between Eucalyptus tereticornis and Eucalyptus camaldulensis occur in north-eastern Queensland. These two species also hybridize spontaneously in plantations and artificial crossing in India showed a striking degree of hybrid vigour; the hybrid, designated as F.R.I.-4 and F.R.I.-5, produced three times the wood volume of Eucalyptus tereticornis at 4 years of age. Eucalyptus tereticornis x Eucalyptus grandis (South Africa) does not have the hybrid vigour, but is resistant to pink disease (Corticium salmonicolor) whereas Eucalyptus grandis is not.

Its rapid growth and its adaptability to a variety of environmental conditions make Eucalyptus tereticornis very promising to be included in trials in South-East Asia on a wider scale. However, testing and selection of locally adapted provenances should receive high priority if Eucalyptus tereticornis is to be utilized to its full potential.

Chippendale, G.M., 1988. Eucalyptus. In: George, A.S. (Editor): Flora of Australia. Vol. 19. Australian Government Publishing Service, Canberra, Australia. p. 324.
Eldridge, K., Davidson, J., Harwood, C. & van Wijk, G., 1993. Eucalypt domestication and breeding. Clarendon Press, Oxford, United Kingdom. pp. 139-143.
Fenton, R., Roper, R.E. & Watt, G.R., 1977. Lowland tropical hardwoods - an annotated bibliography of selected species with plantation potential. External Aid Division, Ministry of Foreign Affairs, Wellington, New Zealand. pp. ETe 1-ETe 38.
Jacobs, M.R., 1981. Eucalypts for planting. 2nd Ed. FAO Forestry Series No 11. Food and Agriculture Organization of the United Nations, Rome, Italy. pp. 494-498.
Lamb, D., Johns, R.J., Keating, W.G., Ilic, J. & Jongkind, C.C.H., 1993. Eucalyptus L'Hér. In: Soerianegara, I. & Lemmens, R.H.M.J. (Editors): Plant Resources of South-East Asia No 5(1): Timber trees: Major commercial timbers. Pudoc Scientific Publishers, Wageningen, the Netherlands. pp. 200-211.
Penfold, A.R. & Willis, J.L., 1961. The eucalypts: botany, cultivation, chemistry and utilisation. Hill, London, United Kingdom. 551 pp.
Pinyopusarerk, K., 1989. Growth and survival of Australian tree species in field trials in Thailand. In: Boland, D.J. (Editor): Trees for the tropics; growing Australian multipurpose trees and shrubs in developing countries. ACIAR Monograph No 10. Australian Centre for International Agricultural Research, Canberra, Australia. pp. 109-127.

E. Boer

Boer, E., 1997. Eucalyptus tereticornis J.E. Smith. In: Faridah Hanum, I & van der Maesen, L.J.G. (Editors): Plant Resources of South-East Asia No 11: Auxiliary plants. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea