The 1997 Indonesian forest fires were caused mainly by slash and burn techniques adopted by farmers in Indonesia. Slash and burn has been extensively used for many years as the cheapest and easiest means to clear the lands for traditional agriculture. Fire is also used during the long fallow rotation of the so-called jungle rubber in Sumatra and Kalimantan to remove most of the biomass, including the woody parts before new plantations are re-established.
Fire may also be deliberately used as a weapon to claim property on the islands and provinces where land ownership is not clear, an action taken by both smallholders and large operators alike. After burning out its previous owner, the smallholder or large operator plants their own crops there, gaining de facto control over the disputed land.[citation needed]
During the fire season, dry fuels readily ignite and lead to large wild fires. In cases like this, fire suppression can be very difficult and costly especially when they reach the highly flammable peat-swamp areas. NASA has linked El Niño to then that causes drier conditions in much of Indonesia. Historically its arrival has been welcomed as time of bounty when mass fruiting of Dipterocarp trees spawn a boom in wildlife activity and bring prosperity to indigenous seed collectors. However, in recent years, large-scale land use change in Indonesia, especially on the islands of Borneo and Sumatra, mean that El Niño is increasingly associated with massive forests fires that spread a choking haze and economic concerns across Southeast Asia.
Underlying and perhaps more far-reaching contributors to this shift in land use and agriculture are the use of "old" woods, such as mahogany and teak, in luxury items. Both are considered unsustainable [3] and though not directly linked to the catastrophic forest fires, they may play a role.