Environmental change and rain forests on the Sunda shelf of Southeast Asia: drought, fire and the biological cooling of biodiversity hotspots

Environmental change during the Quaternary period has caused changes in the composition and structure of vegetation on the Sunda shelf of Southeast As ia. Climatic conditions drier than the present, particularly during the pea k of the last ice age, led to a reduction in the extent of rain forests. Mo st recently, there has been a close association between drought and the occ urrence of major, rain forest fires. Although many rain forest trees show a daptations to periodic drought, this is not the case for frequent or intens e fires. Over evolutionary time-scales, major fires may thus have been larg ely confined to driver vegetation types, such as monsoon and deciduous fore sts, and only infrequently penetrated rain forest areas. Continental-scale distribution patterns for rain forest species reveal a number of biodiversi ty hotspots that are consistent for a broad range of taxonomically unrelate d taxa. These biodiversity hotspots account for a relatively small part of the total extent of rain forest; they may also represent ecologically relat ively stable areas. This paper discusses the location and extent of biodive rsity hotspots on the Sunda shelf within the context of past and present en vironmental change. It finds that whatever the history of biodiversity hots pots, they are increasingly threatened by contemporary environmental change , notably a trend towards increasingly frequent and intense fires. The pape r concludes that the trend is likely to continue, without major changes in those activities that degrade and precondition to fire remaining areas of r ain forest.