Eusideroxylon zwageri
| Bornean ironwood | |
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| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Magnoliids |
| Order: | Laurales |
| Family: | Lauraceae |
| Genus: | Eusideroxylon |
| Species: | E. zwageri |
| Binomial name | |
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Eusideroxylon zwageri Teijsm. & Binn. |
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| Synonyms | |
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Eusideroxylon zwageri is a rare timber tree native to the Brunei, Indonesia, Malaysia and Philippines region. It is known colloquially in English as Bornean ironwood,billian, or ulin.
It is native to Brunei; Flores, Java, Kalimantan and Sumatra in Indonesia; the Sabah and Sarawak states of Malaysia; and the Sulu Archipelago of the Philippines. It is threatened by habitat loss. The government of Indonesia and the state government of Sarawak have formally banned the export of this species. Illegal smuggling continues to be a major problem.
Eusideroxylon zwageri grows in lowland primary and secondary forest up to 625m altitude. It prefers well-drained soils, sandy to clay-loam, sometimes limestone. It is commonly found along rivers and adjacent hills. It requires an average annual rainfall of 2,500–4,000 mm. It occurs scattered or in groups.
This very important tree is one of the most durable and heaviest timbers in the world. It is now threatened by over-exploitation, lack of regeneration and difficulties in cultivation.
Eusideroxylon zwageri is a slow growing (0.5 centimeters per year) tall evergreen tree with a straight bole (usually host to Cassytha, a parasitic vine with leaves reduced to scales, up to half of the tree's height). It is slightly fluted at the base, up to 150–220 cm in diameter. The trunk has many small, rounded buttresses that give the base an elephant-foot like appearance. Individual trees may reach an age of 1,000 years or more. Common commercially exploitable trees attain a height of 30 or more metres (100 ft) with trunk diameters of exploitable trees up to 92 cm (36 inches). Protected trees are towering giants of the forest attaining a height of up to 50 metres and a diameter of 220 cm - though height is routinely reduced by lightning strikes. An Ulin tree discovered in 1993 in Kutai National Park, is one of the largest plants in Indonesia. It is an estimated 1,000 years old, and has increased its diameter from 2.41 to 2.47 metres in the 20 years since its discovery. Its height was however reduced from some 30 metres to only 20 after a lightning strike. Another at Sangkimah in the west of the park has a diameter of 2.25 metres and a height of some 45 metres.
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