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The ulin (Eusideroxylon zwagery) is a large, hardy tree native to Borneo that grows in lowland, tropical rain forests. It is dark in colour, is resistant to both termites and sea water, and is often referred to as the Bornean ironwood.

As its name implies, Bornean ironwood is widely used as a strong building material, in the construction of houses, bridges, power poles, bearings, maritime buildings, and in the shipping industry.

Our Post-Release Monitoring team members from Camp Nles Mamse in the Kehje Sewen Forest, East Kalimantan, have seen this species of tree while observing orangutans in the forest. Bornean ironwood trees grow as high as 50 metres in height, with diameters of up to 220 cm! Bornean ironwoods typically grow straight, with buttress roots extending up to four metres high along the trunk. The straightness and length of its trunk makes it an ideal and uniform building material.  


However, the Bornean ironwood grows at a very slow rate, with seed germination alone taking anywhere from 6 to 12 months. Therefore, the use of ironwood trees needs to be balanced with conservation efforts, and a sustainable management plan must be followed if the survival of the species is to be safeguarded.

We hope that stricter regulations and supervision, both by the central and local governments, will prevent the illegal logging of Bornean ironwood. May this magnificent species grow forever in the forests of Borneo.

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