Common Name: Borneo Ironwood

General Information

Eusideroxylon zwageri is a slow-growing, evergreen tree that can reach a height of 40 - 50 metres. The straight bole can be clear of branches for up to half of the tree's height, and up to 150 - 220cm in diameter[, ]. The bole has many small, rounded buttresses that give the base an elephant-foot like appearance[].
The tree is widely exploited in the wild for its valuable timber, which is one of the heaviest and most durable timbers of South-East Asia[].
This species is one of the most renowned timbers of Borneo, the decline of which was first noted in 1955[]. Population reduction, caused by overexploitation and shifting agriculture, has been noted in several areas[]. Regeneration in logged-over forests is limited and so far the species is only planted on a small scale because the supply of seeds and seedlings is inadequate[]. The tree has therefore been classified as 'Vulnerable' in the IUCN Red List of Threatened Species(2009)[].

Known Hazards

The large fruits are poisonous[, ].

Botanical References

Range

Southeast Asia - Malaysia, Indonesia, Philippines.

Habitat

Generally found in lowland areas of primary forest from around sea level to elevations of 400 metres, in flat or sloping terrain, and also occurs in old secondary forest[].

Properties

Conservation Status	Vulnerable
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	35.00 m
Growth Rate	Slow
Cultivation Status	Wild

Cultivation Details

A plant of the lowland, moist tropics, where it is found at elevations up to 625 metres. It grows best in areas where annual daytime temperatures are within the range 20 - 30°c, but can tolerate 10 - 38°c[]. It prefers a mean annual rainfall in the range 2,500 - 4,000mm, but tolerates 2,000 - 4,500mm[].
Seedlings require some shade, while older trees need plenty of light[]. Prefers well-drained soils in valleys or on hillsides or even low ridges when soil moisture is sufficient[]. Prefers a pH in the range 5 - 6, tolerating 4.5 - 6.5[].
Trees may begin to flower at an age of 15 - 20 years[].
They bear fruits at irregular intervals, often every 2 - 3 years, sometimes annually. Fruits ripen within 3 months after flowering. Seed dispersal is apparently often by water; rich pockets of ulin forest are often found at places where the fruits wash ashore in large quantities along rivers[].
Plants can coppice freely[].

Edible Uses

None known

Medicinal

The pulverized fruits have been used medicinally as a treatment against swellings[]. Some caution is advised, especially if the fruits are taken internally - see notes above on 'Known Hazards'.

Other Uses

The heartwood is yellowish-brown to reddish-brown when freshly cut, but it becomes silvery brown, dark brown or almost black on exposure; the sapwood is sharply differentiated from the heartwood and bright yellow when freshly cut, darkening to yellowish-brown on exposure[]. Freshly cut wood has a fresh, slightly lemon-like odour[]. The wood is very heavy; straight grained, occasionally slightly interlocked; texture moderately coarse and even[].
The wood can be sawn with good result, but it blunts sawteeth fairly rapidly, owing to its hardness; the sawteeth should be kept clean from accumulating oily deposits[]. Because it tends to split in the radial plane when screwed or nailed, the wood must be pre-bored[]. The easy splitting in radial direction makes the wood excellent for making shingles, although sometimes pieces of wood with interlocked grain may cause problems[]. The wood is difficult to glue with synthetic adhesives; furniture, for instance, often fails at glued joints[].
The wood is rated as very durable. Graveyard tests with stakes showed an average service life in contact with the ground of 17.5 years under tropical conditions[]. Stockades and posts have been reported to last over 100 years, and pepper (Piper nigrum L.) support posts and shingles over 30 years. A life of up to 20 years can be expected in marine works[]. The wood is resistant to termite attack, although after long periods of exposure attack may occur. Ambrosia beetle attack is rare, but the wood is more commonly attacked by longicorn beetles, and the sapwood also by powder-post beetles. The wood is very resistant to wood-rotting fungi. The heartwood is extremely resistant to preservative treatment[].
One of the heaviest and most durable timbers of South-East Asia. As such, it is preferably used in marine constructions such as pilings, wharfs, docks, sluices, dams and ships (keels, ribs and decking), or in heavy constructions such as bridges, power line poles, masts, piles and house posts[]. It is also used for the traditional houses ('longhouses') of the Dayak in Borneo[]. Another major use is for roof shingles ('sirap') which are reported to last 50 years to more than a century[]. Less important is its use as frame, board, for heavy duty flooring, floodgates, road pavement and foundations, railway sleepers, fencing, printing blocks, vehicle bodies, sleds for log skidding, furniture, chopsticks, blowpipes, poles (in pepper cultivation) and survey pegs[]. The wood is not suitable for plywood or particle board production[]. It has been esteemed by the Chinese as a coffin wood[].

Propagation

Seeds are often placed horizontally between two beds of grass, or they are covered with 2 - 5 cm of soil[]. Germination usually starts after about 2 weeks (but it may take 6 - 12 months) and the germination rate is approximately 40%[]. Scarification (cutting off the top of the seed or removing the whole outer shell) may improve the germination rate to 70%[]. Nursery-raised seedlings or wildlings of about 40 cm tall, a height reached after 1 - 1.5 years, are planted into the field at a spacing of 3 metres x 4 metres and need shade[].

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