Fire behavior and fire effects across the forest landscape of continental Southeast Asia

Abstract

The massive ENSO-induced fires of 1982–1983 and 1997–1998 that burned across much of Borneo forced a critical re-evaluation of the role of fire in tropical forests. In Southeast Asia the occurrence of fires is generally associated with increasing rainfall seasonality. In aseasonal lowland rainforests fire is rare, but potentially devastating when it occurs. In the strongly seasonal regions of continental Southeast Asia deciduous forests and savannas may burn at low intensity every few years, but have little impact on the majority of trees. Between these two extremes of rainfall seasonality lie landscapes dominated by mosaics of evergreen and deciduous forests for which the role of fire and its potential impacts are poorly understood. Ecologists and conservationists across the region have expressed concern that changing fire regimes due to increasing human pressures and potential climate change may lead to a substantial loss of the evergreen forest component within these mosaics. However, there are few empirical data to address these concerns and to use in the development of robust landscape-scale fire management plans. Here we describe results from a study on the fire ecology of forests at the Huai Kha Khaeng Wildlife Sanctuary in western Thailand that was conducted in the wake of the 1998 ENSO fires that occurred there. We compared fire behavior, tree mortality, and stand-scale impacts of the fires across the three dominant forest types of the region: seasonal evergreen forest, mixed deciduous forest, and deciduous dipterocarp forest. Our data demonstrate that the fires are mostly low-intensity surface fires that generate a low level of mortality across the landscape. Mortality was primarily a function of tree size with 50% mortality occurring in trees ∼2 cm DBH (diameter at breast height). We found no evidence of heightened sensitivity to fire in the seasonal evergreen forest and suggest that the high levels of mortality among evergreen tree species in Bornean forests are indicative of differences in long-term exposure to fire between the seasonal evergreen forests of the continent and the aseasonal evergreen forests of insular Southeast Asia. We discuss these findings in the context of the design and implementation of fire management practices in the seasonal tropical forests of continental Southeast Asia.