Current fire regimes, impacts and the likely changes - IV: tropical Southeast Asia

The Southeast Asian region is experiencing some of the world’s highest rates of deforestation and forest degradation, the principle drivers of which are agricultural expansion and wood extraction in combination with an increased incidence of fire. Recent changes in fire regimes in Southeast Asia are indicative of increased human-causd forest disturbance, but El Nino–Southern Oscillation (ENSO) events also play a role in exacerbating fire occurrence and severity. Fires are now occurring on a much more extensive scale - in part because forest margins are at greater risk of fire as a result of disturbance through logging activities, but also as a result of rapid, large-scale forest clearance for the establish-ment of plantations. Millions of hectares have been deforested and drained to make way for oil palm and pulpwood trees, and many plantation companies, particularly in Indonesia, have employed fire as a cheap land clearance tool; uncontrolled fires have entered adjacent forests or plantation estates, and burnt both the forest biomass and, in peatland areas, underlying peat. Forest fires cause changes to forest structure, biodiversity, soil and hydrology. Repeated fires over successive or every few years lead to a progressive decline in the number of primary forest species. Fire leads to reduction in both aboveground and below ground organic carbon stocks and also changes carbon cycling patterns. In non-peatland areas, losses of carbon from fire affected forest vegetation exceed greatly soil carbon losses, but on carbon-rich substrates, e.g. peat, combustion losses can be considerable. Peatland fires make a major contribution to atmospheric emissions of greenhouse gases, fine particular matter and aerosols and thus contribute to climate change as well as presenting a problem for human health. The scale of emissions is unlikely to reduce in coming decades, since climate modelling studies have predicted that parts of this region will experience lower rainfall in future and greater seasonality. Protecting the rainforests of this region from further fire disasters should be at the top of the global environmental agenda, with highest priority given to peatland areas.