Eucalyptus urophylla (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

Eucalyptus urophylla S.T. Blake

Protologue: Austrobaileya 1(1): 7 (1977).

Family: Myrtaceae

Chromosome number: 2n = 22

Synonyms

Eucalyptus alba auct. non Reinw. ex Blume,
Eucalyptus decaisneana auct. non Blume.

Vernacular names

Timor white gum, Timor mountain gum (En)
Indonesia: ampupu, popo (Indonesian, Timor), palavao preto (Portugese, East Timor).
Vietnam: bạch dàn dỏ.

Origin and geographic distribution

The natural distribution of E. urophylla is confined to the eastern part of the Lesser Sunda Islands (Bali and Nusa Tenggara), occurring principally on the islands of Timor, Alor and Wetar with fewer occurrences on Adonara, Lomblen, Pantar and the eastern parts of Flores. The natural range extends about 500 km between longitudes 122-127 °E and latitudes 7°30'-10 °S. It has been introduced to Java in 1890 and in 1919 to Brazil (as E. alba). In 1966, it was introduced to Australia and since then to many other countries, notably Papua New Guinea, Malaysia, China, Cameroon, Congo, Ivory Coast, Gabon, Madagascar and French Guiana.

Uses

E. urophylla is increasingly used in reforestation programmes and is economically important for wood production. It makes satisfactory fuelwood and charcoal. In Timor, the wood is used for heavy construction and bridging, elsewhere also for framing and flooring. Round wood is used for building poles and fence posts. It is particularly suitable as a source of mid-density to low-density eucalypt fibre for pulp and paper production. The bark has a tannin content of over 10%, but is not used commercially.

Properties

The wood of E. urophylla is moderately durable. The heartwood is pinkish-brown to red-brown, and contains little gum. The basic density is in the range of 540-570 kg/m³, which is comparatively light compared to other Eucalyptus species. The wood is fairly easy to saw. Fibres are relatively short, 0.7-1 mm, and the wood is suitable for bleached chemical pulp and has a good pulp yield of about 50%.

On average, there are 210--470 viable seeds per g of uncleaned seed.

Production and international trade

No statistics on trade are available. Extensive plantations of E. urophylla and its hybrids have been established in Brazil, China, Congo and elsewhere. The most commonly planted hybrid is E. grandis W. Hill ex Maiden × E. urophylla.

Description

Evergreen tree up to 45(-55) m tall, in unfavourable environments a gnarled shrub; bole usually straight, branchless for up to 30 m, up to 1(--2) m in diameter. Bark variable depending on available moisture and altitude, usually persistent and subfibrous, smooth to shallowly and closely longitudinally fissured, red-brown to brown or pearl-grey, sometimes rough especially at the base of the trunk.
Juvenile leaves subopposite, stalked, broadly lanceolate, 10-15 cm × 5-8 cm, discolourous, lateral veins just visible, at 50-70° to the midrib.
Adult leaves phyllodinous, subopposite to alternate, long stalked (12-30 mm), broadly lanceolate and abruptly narrowed into a short tip or lanceolate and tapering into a long drip tip, 12-20 cm × 2-5 cm, lateral veins visible, at 40-50° to the midrib, dark green above, paler green below.
Inflorescence an axillary, simple umbelliform condensed and reduced dichasium called a conflorescence; umbels solitary, 5-8-flowered; peduncle somewhat flattened, 8-22 mm long; pedicel angled, 4-10 mm long; flowers regular, bisexual; flower buds ellipsoid to obovoid, shortly pointed to rotund, 10-14 mm × 6-10 mm, divided into a calyx tube or hypanthium (lower part) and an operculum (upper part), equal or slightly longer than the calyx tube, which is shed at anthesis; stamens numerous, on a staminophore.
Fruit a dry thin-walled capsule enclosed in a woody hypanthium, opening with 3-5 included to partly exserted valves, obconical to cup-shaped, 6-14 mm × 7-18 mm; disk almost flat to obliquely depressed.
Seed small, 4-6-angular to more or less semi-circular, black.
Seedling with epigeal germination; cotyledons usually bilobed to about the centre; first 5-7 pairs of leaves opposite, subsequent pairs subopposite.

Growth and development

Mature seed germinates readily under favourable conditions and does not require pregermination treatment. Seedlings usually reach 25 cm in height in 10-12 weeks. In conditions of high relative humidity, young seedlings may be susceptible to damping-off.

E. urophylla retains its leaves during the dry season, and grows actively when moisture and temperature conditions are favourable, with a strong apical dominance. In dry locations and on shallow soils on mountain ridges, apical dominance is less pronounced and plants may develop into shrubs. In Thailand, early growth of two different provenances during the first year was 2.4-6.2 m in height and 3.9-7.4 cm in diameter. In Peninsular Malaysia, growth during the first four years was 1.7-3.5 m/year in height and 2.0-3.9 cm/year in diameter. In East Java, a trial of trees aged 7 years and 9 months showed a mean height of 27 m and a mean diameter of 22.8 cm. Very rapid initial growth has been reported from the Solomon Islands, but the trees remained thin-stemmed and developed a thin canopy, most probably because the climate was too humid. In general, progenies from low altitudes in Flores, Alor and Timor grow fastest.

Flowering usually starts within 2 years after planting and seeds are produced abundantly by 4 years of age. In Brazil, flowering of two-month-old seedlings has been observed occasionally. In its natural habitat, peak flowering of E. urophylla is strictly tied to the rainy season in January--March. Pollination is by insects. Fruits reach maturity about 4 months after flowering, in May-July(-August).

Other botanical information

E. urophylla appears to be one of the most variable of all eucalypts, with considerable variation in morphological features such as adult leaf size and expression of a drip tip, bud characteristics, fruit size and shape. There are also differences between the seedling, juvenile, intermediate and adult leaves. The extreme variation in bark characteristics appears to be associated with differences in available moisture and altitude. Boles are mainly smooth at lower altitudes and under drier conditions. Smooth boles with rough bark at the base are found below 1000 m altitude in Alor and Flores, at 1000-2000 m in Timor the boles are usually entirely covered with rough bark, above 2000 m in moist conditions the bark is usually subfibrous. Recent analyses indicate that specimens from high altitude sites in Timor and from dry sites in Wetar are distinct from the residual E. urophylla. These have been designated E. orophila L.D. Pryor and E. wetarensis L.D. Pryor respectively.

E. urophylla has been distinguished as a separate species only recently. It has been widely cultivated under the name E. alba Reinw. ex Blume or as E. decaisneana Blume. In Java, the name E. platyphylla F. Muell. was used for E. alba. As a consequence, considerable confusion exists about the true nature of several provenances. Where natural populations of E. urophylla meet those of E. alba, hybrids are frequently encountered and introgression of characters may take place. This enhances the confusion about true identities of provenances. E. alba is a smaller tree of poor shape, the adult leaves are generally broader (2-5 cm), concolourous, and lack the characteristic drip tip, while its fruit is hemispherical to obconical and 4-7 mm × 5-8 mm. Hybrids may be recognized by their white, smooth trunk, their larger and less numerous leaves but the extreme variability in the bark characteristics of E. urophylla can make identification of hybrids difficult.

The occurrence of hybrids between E. alba and E. urophylla as well as between the latter and E. saligna or E. tereticornis enhances the confusion.

Ecology

E. urophylla (including E. orophila and E. wetarensis) has the largest altitudinal range of any eucalypt, extending from 1000-2960 m in Timor, from 70-800 m in Wetar and from 300-1100 m in Flores and the smaller islands to its east. It is frequently found as the dominant species in secondary montane forest. At lower altitudes and in drier, exposed locations usually below 1500 m, it is often replaced by E. alba. The natural range of E. urophylla is in the humid and sub-humid climatic zones. At about 400 m altitude the mean maximum temperature of the hottest month is 27-30 °C, which may drop to only 15-21 °C at 1900 m. Mean maximum temperature of the coldest month is 8-12 °C. In Timor many of the E. urophylla forests occur at about 1000 m altitude, where mist and fog are common, annual rainfall is 1300-2200 mm, and the dry season is (2-)3-4 months. On other islands, drier conditions prevail with rainfall of 600-1500 mm, and a dry season of 5--8 months.

E. urophylla grows on mountain slopes and in valleys. It develops best on deep, moist, well-drained, acidic or neutral soils derived from volcanic or metamorphic rock. It is also commonly found on basalts, schists and slates, but rarely on limestone.

Propagation and planting

Nursery establishment is generally by sowing untreated seed in germination beds. Mature seed germinates readily in 7-12 days and does not require any pretreatment. Damping-off can be prevented by reduced watering and shade, and allowing ventilation. The seedlings are transplanted into polythene bags when they have developed 2 pairs of leaves. The potting medium is usually a freely draining mixture of loam and sand. Seed may also be sown directly into containers and thinned out after germination. Seedlings are planted out in the field when they reach a height of about 25 cm, 10-12 weeks after sowing.

In Brazil, E. urophylla or hybrids of E. urophylla and E. grandis are raised using rooted cuttings derived from stump sprouts. After coppicing, when the new sprouts are 60-80 cm long, they are removed and divided into cuttings with two pairs of leaves. The leaves are treated with a fungicide. The cuttings are dipped in a rooting hormone and then set to a depth of 4 cm in polythene bags filled with subsoil clay. They are kept under 50% shade and intermittent mist spray for 30-40 days. At this stage, roots have formed and the cuttings are moved to full sunlight and 1 g of complete fertilizer is added to each bag. They are planted out when 70-80 days old. After culling clones with poor rooting capacity, 80% rooting is generally achieved in commercial production. Tissue culture has proved successful on an experimental scale in Indonesia; the explants are taken from 3-week-old material. The hybrid E. urophylla × E. grandis has been planted using tissue cultured plants on a pilot scale in Guangdong Province, China.

Intensive site preparation by ploughing is beneficial; on compacted sites, deep ripping may also be used. NPK fertilizer is applied in each planting hole. Spacing varies with the purpose of the plantation. For pulpwood, 3 m ×> 2 m is commonly used, for fuelwood or poles planting may be closer.

Husbandry

Plantations are invariably established using containerized seedlings or cuttings. It is essential to keep the planting site weed-free, at least until the trees reach 6 months of age, since eucalypts are highly sensitive to competition. After 6 months, their dense foliage should suppress competing vegetation. Thinning is done every two years from the age of 3 years onwards, when the initial spacing is 3 m × 2 m. E. urophylla has good coppicing ability and trees can be expected to produce at least 3 coppice rotations after the initial seedling rotation. The tree is fairly resistant to fire.

Yield

An annual increment of 20-30 m³/ha with bark at 5-10 years of age is usually obtained. Better provenances can yield up to 50 m³/ha per year on favourable sites. Hybrids generally yield considerably higher, e.g. a mean annual increment of E. urophylla × E. alba in Congo was 30-35 m³/ha, while that of E. urophylla × E. grandis in Brazil was 35-70 m³/ha with individual plots yielding over 100 m³/ha annually. Mass-propagated cuttings from selected hybrids of E. urophylla with E. tereticornis J.E. Smith, E. alba and E. grandis in Cameroon gave annual increments of over 30 m³/ha in an 8-year rotation.

Diseases and pests

In conditions of high relative humidity, young seedlings may be susceptible to damping-off. In Indonesia, death of 2-month-old seedlings has been attributed to attack by root fungi such as Botryodiplodia sp., Fusarium sp. and Helminthosporium sp. A canker disease caused by Cryphonectria cubensis is found on E. urophylla in West Africa and South America. Although it is much more resistant than E. grandis or E. saligna J.E. Smith, some provenances are quite susceptible, especially in humid tropical lowland conditions. Seedlings and small trees of E. urophylla are susceptible to termite attack and stem borers such as Zeuzera coffeae and these may also cause damage to older trees. In the Solomon Islands, dieback attributed to the coreid insect Amblypelta cocophaga was observed in 3-4-month-old plantings. The introduction of the ant Oecophylla smaragdina and clearing the undergrowth controlled the attack satisfactorily.

Genetic resources

Since 1963 more than 15 expeditions have collected seed from the natural range of E. urophylla. Much of this material has been used in Indonesian domestic planting programmes, but a significant amount has been established elsewhere. Comprehensive provenance trials exist in Indonesia, Thailand, China, Congo, Ivory Coast, Malawi, Brazil, Colombia, Puerto Rico, and elsewhere. It appears that provenance variation is closely related to the altitudinal gradient of the seed sources. The CSIRO Australian Tree Seed Centre in Canberra holds a comprehensive collection of seed samples of E. urophylla from throughout its natural range. E. urophylla disappeared from the Indonesian island of Solor, but its genetic base is not seriously affected by man as the trees are generally found in rugged and remote areas and are fairly resistant to fire.

Breeding

An isozyme survey of E. urophylla has revealed a rather unstructured isozyme differentiation pattern with small genetic distances between populations. Only populations from the island of Wetar clustered together on the basis of their isozyme genotypes. This lack of genetic variability between populations contrasts with the high degree of differentiation in morphological characters and growth rates in provenance trials. The main outcome from the provenance trials has been the demonstration that provenances from altitudes of above 1500 m perform poorly in the lowland tropics. Moreover, those provenances from lower altitudes (300-1100 m) and from drier locations grow well in humid and sub-humid tropical and subtropical conditions with a dry season of 1-5 months in the coolest part of the year.

Breeding programmes in Brazil, China, Congo and Indonesia have selected superior individuals in provenance trials and plantations or superior offspring in progeny trials. In Brazil E. urophylla has been hybridized with E. grandis to produce vigorous hybrids for clonal pulpwood plantations. In Cameroon, hybrids with E. tereticornis and E. alba have been used similarly. These hybrids are increasingly being planted following mass vegetative propagation by cuttings. Breeding programmes have focused on optimizing growth rate, stem straightness, wood density and coppicing ability, while rooting capacity of cuttings is an additional prerequisite for mass vegetative production.

Prospects

E. urophylla plays an important role in afforestation in a small but growing number of countries. However, it has the potential to become much more widely used in humid and sub-humid tropical regions, as it belongs to the most productive of the low-latitude eucalypts. Its fast growth, coppicing ability, adaptability to a range of environments, early canopy closure, relative resistance to fire and to diseases and pests, and the various products which can be obtained from the wood, make it a very useful tropical tree.

Literature

Blake, S.T., 1977. Four new species of Eucalyptus. Austrobaileya 1(1): 1-10.
Eldridge, K., Davidson, J., Harwood, C. & van Wijk, G., 1993. Eucalypt domestication and breeding. Clarendon Press, Oxford, United Kingdom. pp. 144-153.
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. 503--506.
Martin, B. & Cossalter, C., 1975. Les eucalyptus des Iles de la Sonde [Eucalypts in the Sunda Islands]. Revue Bois et Forêts des Tropiques 163: 3--25; 164: 3--14; 165: 3-20; 166: 3-22; 167: 3-24; 168: 3-17; 169: 3-13.
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.
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.
Pryor, L.D., Williams, E.R. & Gunn, B.V., 1995. A morphometric analysis of Eucalyptus urophylla and related taxa with descriptions of two new species. Australian Systematic Botany 8: 57-70.
Turnbull, J. & Brooker, I., 1978. Timor mountain gum - Eucalyptus urophylla S.T. Blake. Forest Tree Series 214. Commonwealth Scientific and Industrial Research Organization, Melbourne, Australia. 2 pp.
Umboh, I., Setiawan, I., Kamil, H., Yani, S. & Situmorang, J., 1989. L'application de techniques de culture in vitro à la multiplication d'espèces forestières tropicales en Indonésie [Use of in vitro culture techniques for multiplication of tropical forest tree species in Indonesia]. Bulletin de la Société Botanique de France, Actualités Botaniques 136(3--4): 179-184.

16, 52, 62, 130, 193, 322a, 343, 540, 659, 715 (Timbers)

Main genus page

Eucalyptus

Authors

C.C.H. Jongkind (selection of species)
J.W. Turnbull & J.C. Doran (Auxiliary plants)