Belian trees at the Ulu Ulu Resort

Fruit, seeds and leaves of Belian or Ulin  (Borneo Ironwood)  growing at the Ulu Ulu Resort, Temburong, Brunei.

Before the introduction of  chemical wood preservatives to Borneo, Belian wood was prized above all other timbers for outdoor construction because it was too hard to be eaten by termites and resisted fungal decay indefinitely. Despite the fact that saws used on Belian soon became blunt and the heavy logs were difficult to transport because they sank in water (sinkers), the supplies of Belian logs were soon exhausted  and the only places you will still find Belian today are  in forest reserves and national parks.

Two very similar, closely related  species of Belian tree are found in Borneo, Potoxylon melangangai  (NW Borneo) and Eusideroxylon zwagerii (rest of Borneo). This sign was photographed next to a tree at Belalong Field Centre 500m up river from the Ulu Ulu Resort.

These are seeds and dried fruit from the Belian tree growing at the Belalong Field Centre.

These are fallen seeds  from the two Belian trees growing in the center of the Ulu Ulu Resort. One of them grows next to the steps that go down to the boat landing and the other grows  next to the stream that flows under the walkway halfway towards the  far (downriver)  end of the cabins. Note that the seeds can be very variable in size and shape.

When ripe ,the large seed is covered by a thin, very, very, slimy pulp. When this pulp is physically removed the seed is so slippery it is impossible to hold in the hand. The most likely explanation is that the large seed evolved to be swallowed whole and subsequently defecated by rhinos a long distance away.

Leaves of the Belian tree growing next to the stream at the Ulu Ulu Resort.

Borneo’s very hot and very wet climate is the perfect environment for plant growth (such as the lichens growing on this sign)  as well as the perfect environment for  wood eating fungi. Belian is unique amongst Borneo timbers in possessing such hard heavy decay resistant wood.  Belian wood is so dense that Belian logs had to be tied between floater logs to transport them by water to the saw mills. Inevitably many Belian logs sank in storms on the way to the mill and today there is an active industry in Borneo where experienced divers hunt for these “sinkers”  and attach inflatable bags to reclaim them. Even 50 years later the belian timber is as good as new.