Ramin (Gonystylus bancanus), a timber exported by Indonesia and Malaysia, is at the centre of a controversy over whether the species should be banned from the timber trade. Ramin grows in peat swamp forests and such forests are disappearing because after extracting the timber, the swamp is often drained, and the land converted to agriculture. There is no incentive to save the forest because the ramin fails to regenerate. After 50 years of research, foresters have not figured out why ramin does not regenerate in nature.
Curious to find out more, I purchased 8 saplings (4 ft tall and rooted in polybags of clayey soil) from the FRIM nursery and took them home for observation. I placed them under a small tree in a row, watered them well, and went away on holiday for two days. It did not rain during those two days. When I came back, I found to my great surprise that the tough leathery leaves of the plants, especially of the four plants closest to the edge of the shade, had begun to dry and curl up. Six leaves had already been shed on the ground. I watered the plants liberally, but next day, another 60 leaves were shed, including leaves that had re-absorbed water and looked healthy. Next day, three more leaves were shed and the day after, another three were shed. The shedding stopped after that. By then two saplings had shed most of their leaves, one sapling was totally bare, and one had a few dry and dead leaves hanging on it.
Before interpreting these observations, let me digress a little. When a tree is stressed from shortage of water, it has three levels of reaction. If the stress is not severe, the tree recovers when watered and does not show any damage. If the water shortage is more acute, the tree forms an 'abscission layer' at the base of each leaf stalk, which has the effect of cutting off the leaf. By cutting off its leaves, the tree saves itself from drying out. If the drying is sudden and drastic, there is no time for abscission layers to form, and the leaves dry up and die on the tree.
Incidentally we can tell a lightning-struck tree from a tree dead from disease, because in the former the leaves are not shed whereas in the latter, they are.
In the case of my ramin plants, the four better-shaded plants recovered on watering. Of the four more-exposed plants, the one with dead leaves hanging on it is probably dead. The other three, having shed all or most of their leaves, are now stable and should recover.
It has certainly been a surprise to me that ramin is so sensitive to water stress. This is has not been reported before, but then, not many foresters take their experiments home and watch them closely.