Sometimes you see propeller trees (Dipterocarpus spp, Dipterocarpaceae) with hollows blackened by fire. Many tourists believe it is something religious, especially if the tree is old and wrapped with orange girdles. What you see is a tree used for resin harvesting. Harvesting is done in the dry season by carving a hole into the tree trunk about one meter from the ground. A fire is lit to enhance the flow of resin. After the flow stops the resin is harvested and when more is needed the farmer makes the hole a bit deeper and repeats the process. The farmers would keep carving until they reach the centre of the tree and then a new hole is made.
All members of the Dipterocarpaceae family have resin, but the quality and amount varies between tree species. A good tree with a 2 m girth may produce 9 kg/season.
Why would anyone do this?
The practice has been common in India, Bangladesh and Southeast Asia including Indonesia. The products are oil and dammar (the solidified resin). The oil is used as a medicine (skin diseases), ink, varnish, paint solvent, to prevent iron tools from corrosion, water proofing bamboo baskets to carry water and even to make cloth water and insect proof by dissolving caoutchouc. Traditionally, the latex of the Southeast Asian gutta-percha (Palaquium gutta, Sapotaceae) was the source of caoutchouc.
The dammar has been used as a fumigant, for making torches, incense, in medicine, shoe polish, to harden wax, as a cement, or in cosmetics. The now extinct (?) nomadic hunting tribes used to mix the resin with bees wax and red laterite soil to fasten arrowheads and spearheads.
Mixed with dammar or saw dust the oil is also used to caulk wooden boats. When the carpenters fixed up the Dokmai Garden teak log canoe I asked what they used, romantically imagining a paste of teak saw dust and oleoresin from the propeller tree. “Epoxy” was the answer! Like in the west, a lot of the traditional knowledge has been lost in favour of industrially made products, saving time. However, for any permaculture project it is fun to explore and test the old ways.
Bear in mind though that a tree may die from harvesting resin, and the timber is usually considered poor compared with timber from unharmed trees. This practice originates from a time when the forests were vast and humans scarce (6 million Thais at the turn of 1900, 67 million 111 years later…). The monks wrapping the tree is an expression of their concern. The tradition of harvesting resin from propeller trees is becoming rare and will die out with the eradication of poverty.
Some of these facts were derived from a most interesting book which you can download for free: Appanah & Turnbull (1998) A review of dipterocarps: taxonomy, ecology and silviculture.
Text and Photo: Eric Danell