Bornean ironwood (Ulin)

Appearance & recognition

Eusideroxylon zwageri is a large forest tree with buttressed roots, flaky grey-brown bark and leathery leaves. Ulin is a locally important name, but a timber label alone is not a scientific identification. Its native range includes Borneo and Sumatra, rather than Borneo alone.

How the plant grows

This Lauraceae tree has large buttresses, leathery leaves and slow-growing, very durable wood. Its large seeds require time to establish, and a mature canopy tree cannot quickly be replaced by a seedling. Ulin is native to Borneo and Sumatra. The connection to Kutai National Park places a named species within a real lowland forest, where its trunk, roots and crown contribute to forest structure.

Materials & other uses

The density and durability behind the name ironwood explain its long-standing use in posts, flooring and other structures exposed to tropical conditions. Timber use and living-tree ecology should be read together: slow replacement makes the retention of seed trees and forest regeneration particularly important. A timber trade name is not a licence to cut a tree, and the value of the wood does not establish sustainable sourcing.

Ecological relationships

At Sepilok, maroon langurs eat immature ironwood seeds before the protective stone becomes fully lignified. This timing matters: the observation concerns developing seeds, not an ability to break every mature stone.

A study of food plants in the Wehea–Kelay landscape also identifies ulin as a food resource for Bornean orangutans. The cited inventory does not establish which part was eaten; laboratory bark samples should not be mistaken for a feeding observation.