8 - The fire theory I. Field evidence

Summary

Numerous researchers working throughout the geographic range of Australian rainforests have advanced the theory that rainforest boundaries are controlled by fire. This is an old idea, possibly first advanced by the Czech botanist Domin (1911). At the heart of the theory is the assumption that rainforest tree species are ‘fire tender’. Francis (1951) wrote that ‘one of the most marked differences between the constituents of rainforests and those of the open Eucalyptus forests is their behaviour towards fire. In most if not all cases the rainforest constituents are killed even by slight contact with or proximity to the fires which periodically sweep through many of the Eucalyptus and open forests of Australia’. Similarly, Webb (1968) argued that the difference in the ability of rainforest and non-rainforest vegetation to tolerate fire ‘is reflected in the remarkably sharp boundaries of fire-sensitive raingreen forests in the tropics and subtropics, which is related to the exclusion of fire, virtually on an all-or-nothing basis’. However, the supporting evidence is limited and often circumstantial. My aim in this chapter is to review the Weld evidence that fire is critical in controlling rainforest boundaries throughout Australia. Evidence from the humid tropics, monsoon tropics, subtropics and temperate regions will be considered in turn.

Humid tropics

Webb (1968) argued that, in the tropics, rainforest and non-rainforest vegetation is in a dynamic balance controlled by fire frequency, soil fertility and topographic settings such as ‘rocky outcrops and gullies, especially in the lee of fire-bearing winds’.