Eusideroxylon zwageri has a very slow growth rate of mean radial growth of 0.058 cm per year. It is a canopy species in primary forests. The species is considered unsuitable for large-scale plantations due to slow growth and inadequate seed and seedling supply. Manual selection of trees in natural forests is common.
The heartwood when cut is coloured light brown to almost bright yellow. During the aging process the heartwood darkens to deep reddish brown, very dark brown or almost black. The sapwood is bright yellow when cut, and darkens slightly. The wood texture is fine and even, with a straight grain or only slightly interlocked. The timber retains a pleasant lemon odour. This odour, along with the woods’ natural high lustre, make it prized by cabinet-makers and fine furniture craftsmen.
The wood is dense (0.85 – 1.1 g/cm3)? and texture is moderately fine to fine and even. Also attractive to users is the resistance to insects, bacteria, fungi and marine borers. The wood has anti-bacterial properties (for local medicinal use) Vessels are diffuse-porous, medium-sized and generally evenly distributed, arranged in short radial rows (2-3 vessels). Moderate abundancy of aliform paratracheal parenchyma. Growth rings boundaries are indistinct or absent. Tyloses are often present.
The wood has a radial shrinkage rate of 2–4.5% and a tangential shrinkage rate of tangential 4.5–7.5%. The timber dries slowly, and care is needed to avoid checks and splits.
The wood is famed for its easy working characteristics, despite high density. The wood planes, bores and turns cleanly, producing smooth and often lustrous surfaces. Nailing requires pre-bores prior to nailing. Saw blades and cutting instruments are only moderate blunted during working the timber. Apparently, the wood is difficult to glue with synthetic resins.
Durability: heartwood is rated as very durable – immune to termite attack; service life of up to 100 years in direct soil contact and more than 20 years for marine work in tropical waters has been reported.
Due to the excellent resistance to bacterial, fungal, insect and marine borer attack the wood is highly prized for many outdoor uses. Additionally, the wood’s high density and easy workability lend it to particularly desirability in maritime structures, dock construction and ship building, especially Indonesia’s famous pinisi sail-boat. Common local uses include: House construction, door construction, water butts and troughs, boat building (Pinisi), tools, tool handles, talisman, jewellery, medicinal slivers (for wounds, cuts, abrasions, bites and tooth-ache/infection), bridges, blowpipes and spear shafts.
Internationally, it is renowned for heavy construction such as a buffer between transportation trailers and heavy steel fabrications (such as boilers, pressure vessels, reactors and many others). It is also frequently found in dry docks as a timber to separate the hull of ships from the steel supporting stands. Other uses include use in boats and ships, industrial flooring, roofing (as shingles), fine indoor and outdoor furniture, coffin wood (esteemed by Chinese due to ability to withstand rot and insect attack) and tool handles (especially those exposed to continual high impact (the wood does not splinter and thus injure hands, eyes or endanger the operator on catastrophic failure) such as shovels, axes, block splitters, sledge hammers, heavy mallets, demolition hammers, mattocks, picks, hoes and hammers). Some expert cabinet-makers treasure an ulin-headed carpenter’s mallet as an excellent intermediate density hammer face between the usual wood and a metal one and is able to quite easily tap or “whack” stubborn highly polished metal fixtures without damage to the face or the fixture.
Other sources indicate that ulin wood is often used for marine constructions such as pilings, wharfs, docks, sluices, dams, ships, bridges, but also used for power line poles, masts, roof shingles and house posts and to a minor extent as frame, board, heavy duty flooring, railway sleepers, fencing material, furniture etc.
The decline of this species which was first noted in 1955. Browne (1955) stated: “Our surviving supplies of Belian are by no means very large and undoubtedly dwindling.” Population reduction has been noted in the following regions: Kalimantan, Sumatra, Sabah, Sarawak, and the Philippines. IUCN has categorized it Vulnerable A1cd and A2cd. CITES listed II Bi (unsustainable level of exploitation from the wild for international trade). Regeneration in logged-over forests is limited.
The species is threatened by over-exploitation, predominantly by illegal migrant loggers. Current demand for the timber is fueled for its esteem among Chinese as a coffin wood (as it is resistant to insect and rot). Included in list of vanishing timber species of the Philippines and considered almost extinct in Sabah. In Java and Sumatra it exists solely in National Parks. Currently the situation is assessed as a serious depletion of stands. The species is only planted on a small scale because the supply of seeds and seedlings is inadequate. The world-famous IPB Bogor Agricultural Institute (Institut Pertanian Bogor) is currently breeding a generation of plants more hardy than the wild harvested seeds