Common Name: Swamp Mahogany

General Information

Eucalyptus robusta is an evergreen tree normally attaining heights of 25 - 30 metres and diameters of 100 - 120cm, though there are giant specimens that were planted in Hawaii that are as tall as 55 metres with a bole 25 metres tall[]. The bole is typically straight and branch-free for about half the height of the tree[]. Trees growing in the open have crowns with long, spreading, irregular and brittle branches, forming a dense canopy, whilst when growing in closely spaced plantations the branches are almost erect so that little crown spread occurs[]. In plantations in humid climates, some of the trees form aerial roots on the main bole as far as 6 metres above the ground[].
The tree is harvested from the wild for use as a medicine and source of materials. This species is one of the most widely planted Eucalyptus timber species, and it has been introduced into many tropical subtropical, and warm-temperate areas, including many countries in tropical Africa[]. It is also sometimes grown as an ornamental and to provide shelterbelts.

Known Hazards

None known

Botanical References

,

Range

Australia - New South Wales, southern Queensland.

Habitat

Found mainly in swamps and on the edges of coastal lagoons and rivers where it is subject to periodic flooding[].

Properties

Weed Potential	Yes
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	30.00 m
Growth Rate	Fast
Pollinators	Bees, Insects
Cultivation Status	Cultivated, Wild

Cultivation Details

Eucalyptus robusta is a plant of the lowland subtropics but, remarkably, it can adapt to a wide variety of conditions, from equatorial regions with maximum temperatures of about 35°c, to more temperate climates where it can endure frost, provided the frosts are not severe[]. It grows naturally at elevations up to 100 metres in areas where the mean maximum temperature in the hottest month is 30 - 32°c, and the mean minimum of the coldest month is about 3 - 5°c[]. Throughout its native range, from 5 to 10 light frosts occur each year[]. It has proved to be very adaptable in the tropics, where it can grow from sea level to elevations of 1,100 metres with a mean annual rainfall that ranges from 1,000 - 6,350 mm[].
Requires a sunny position[]. Succeeds on a range of soils, but prefers stiff clays and leached sandy loams[]. The tree is exceedingly tolerant to prolonged flooding, so it is extensively planted in swampy areas and along rivers[]. Tolerant of very acid soils[].
Whilst most Eucalyptus species, grown in small numbers outside their native range, can be an attractive and useful addition to the landscape, certain species (including this one) are more problematic. When grown in monocultures, especially outside their native range, they can become an environmental disaster. They are voracious, especially in their use of water; they are allelopathic, inhibiting the growth of the native flora; they reduce habitats for native fauna; and encourage the worst possible attitudes to land use and conservation[].
Trees start flowering when they are 3 - 5 years old. Seed dispersal is mainly by wind. The tree regenerates freely, and dense thickets of saplings can be found near old stands[].
A fast growing tree, it has reached a height of 27 metres in 15 years from seed in tropical plantations[].
The annual growth in height is usually 1.8 - 2.4 metres during the first few years, slowing down to 1.5 - 1.8 metres later[].
The plant grows well in plantations on good sites, but because of its ability to grow on both poorly drained and draughty locations, it is usually planted on adverse sites[]. It regenerates in areas flooded with fresh water, and its roots appear to be able to penetrate the heavy clays found in these conditions to reach the aerated soils below[]. The growth habit also helps it to establish on difficult but not necessarily flooded soils in localities widely different from its normal habitat[].
The tree can send out aerial roots from its trunk[].
Plants coppice well up to the age of 25 years[].
It recovers well from fire, sending out shoots from relatively small branches a few centimetres in diameter[].
Under optimal conditions, the tree begins flowering by the end of its third growing season. More commonly, trees begin flowering when they are 5 years old[]. In tropical areas, such as Hawaii and Puerto Rico, flowers may appear at almost any time of the year[].
Planted seedlings are susceptible to competition and shading, and generally require two weedings in the first six months[].
The length of rotation is largely determined by the product desired. For fuel wood, the tree is sometimes grown in plantations on a 4 - 5 year rotation; for pulpwood an 8 - 10 year rotation is appropriate; whilst saw logs can be produced in plantations or natural stands using 30 - 60 year rotations[]. Most Eucalyptus robusta plantations are regenerated from coppice shoots.
The leaves are aromatic and, when crushed, have a spicy, resinous odour[].
Eucalyptus species have not adopted a deciduous habit and continue to grow until it is too cold for them to do so. This makes them more susceptible to damage from sudden cold snaps. If temperature fluctuations are more gradual, as in a woodland for example, the plants have the opportunity to stop growing and become dormant, thus making them more cold resistant. A deep mulch around the roots to prevent the soil from freezing also helps the trees to survive cold conditions[]. Many members of this genus are remarkably adaptable however, and there can be a dramatic increase in the hardiness of subsequent generations from the seed of survivors growing in temperate zones[].

Edible Uses

None known

Medicinal

The tree is reported to have significant antimalarial activity[].

An infusion of the leaves is used in both Africa and China for treatment of malarial fever[]. In Mauritius and Réunionthe leaves are used for baths, inhalations and infusions to treat fever, colds, cough and influenza. Inhalation is also recommended for treatment of asthma and sinusitis, and infusions are taken against diabetes[].
A decoction of the leaves is used in baths to treat stiffness, rheumatism and epilepsy[]. In Madagascar a handful of buds is rubbed and squeezed, and the sap is applied to the nostrils to relieve headache[].

The essential oil has shown antibacterial and antifungal activity[].
Ethanol extracts of the leaves have shown antioxidant activity[].
Phenolic compounds with activity against the malaria-inducing protozoan Plasmodium bergheihave been isolated from the leaf[].

Agroforestry Uses:

The tree is used in reforestation schemes and is also sometimes planted to stabilize dunes. It is suitable for planting in coastal areas as shelterbelts. Although intolerant of salt spray, it is quite wind firm. It is often used as a windbreak, even though the trees often become deformed by continuous exposure to wind[, ].
Because of their rapid growth, Eucalyptus species use a relatively large amount of water and can be used as pumps to lower the water table and help dry wet sites[, ]. This species has been used very successfully in to dry swampy ground, making it possible to grow less flood-tolerant species on the same site[].
The flowers are a source of nectar and pollen for bees[].

Other Uses

The gum in the trunk contains about 30% tannin[].
The bark contains over 8% tannins[].
The dried leaves yield up to 41% tannin[].

The essential oil yield from the leaves is 1.7%, with the characteristic constituents being piperitone, rho-cymene, linalool, 1,8-cineole, terpinen-4-ol, citronellyl acetate and alpha-terpinol[].

The heartwood is pale red when freshly cut, turning orange-red or red-brown with age; it is clearly demarcated from the up to 5cm wide band of pale brown sapwood. The grain is interlocked, texture coarse. Quartersawn surfaces sometimes have a ribbon figure of light and dark stripes. The wood is fairly heavy, moderately hard, strong, durable and able to be used in moist conditions, resistant to attacks by fungi and most insects, including marine borers, and moderately resistant to termite attack. The high shrinkage, coupled with the interlocked grain, means the wood requires careful drying. During drying distortion and splitting may occur; serious degrade can be avoided by air drying to a moisture content below 30% before kiln drying. The wood is not stable in service. The wood works well and takes a good polish. It is somewhat abrasive, and planing may be affected by interlocked grain. Therefore, slow speeds and a cutting angle of 20° are recommended. Sawing and working properties are generally good, although gummy exudates may clog up saws. The wood holds nails well, but pre-boring is necessary to avoid splitting. It turns well, and paints and waxes satisfactorily. Gluing is fairly difficult. The wood is not suitable for steam-bending. It is used for general construction and for poles, fencing, and wharf and bridge work. Other uses include pallets, house siding, flooring, ordinary furniture, interior trim, and panelling. Because of its strength and durability, it is also commonly used for mine props, railway sleepers, fence posts, stakes and gates. The stakes last a long time in the ground and can be driven repeatedly without splitting. The timber is also used for pulpwood, but the pulp is dark reddish-brown and is not as good for this purpose as some other species of Eucalyptus[, ].
The wood makes an excellent fuel and is good for making charcoal[, ]. It has an energy value of 19,600 - 20,500 kJ/kg[].

Propagation

Seed - surface sow late winter/early spring in a sunny position in a greenhouse[, , ]. Species that come from high altitudes appreciate 6 - 8 weeks cold stratification at 2°c[]. Pot up the seedlings into individual pots as soon as the second set of seed leaves has developed, if left longer than this they might not move well. Plant out into their permanent positions in early summer and give them some protection from the cold in their first winter. The seed can also be sown in early summer, the young trees being planted in their final positions in late spring of the following year. The seed has a long viability[].