Where has all the fire gone? Quantifying the spatial and temporal extent of fire exclusion in Byron Shire, Australia

摘要

Fire is a major determinant of vegetation structure worldwide, and structural vegetation change following fire exclusion is well documented throughout Australia. Such changes include the displacement of treeless ecosystems by forest and the transition of open forest to rainforest. These changes displace essential habitat for myriad plant and animal species and are likely drivers of localised species extinctions. Despite these potential consequences, research identifying the spatial extent of fire-excluded ecosystems is largely absent from the ecological literature. This study identifies the spatial and temporal extent of fire exclusion in Byron Shire in north-east New South Wales. GIS analysis compared modern fire history with recommended fire intervals for the maintenance of fire-dependent vegetation types. Fire exclusion (low-frequency fire) vastly exceeded high-frequency fire, comprising 99.1% of areas affected by inappropriate fire frequency. Most fire-dependent vegetation was fire-excluded, with less than 10% within recommended fire interval thresholds. Most affected areas were fire-excluded for multiple recommended fire-return cycles, increasing the likelihood of vegetation change and localised extinctions. These findings demonstrate the operation of a major threatening process affecting Byron Shire's biodiversity that has previously been little recognised. A growing body of ecological literature suggests that irreversible change to fire-excluded vegetation is likely wherever plant growth resources are sufficient to enable transition. Irreversible vegetation change and rapid species declines have been reported for several communities in Byron Shire, and there is compelling evidence that further change may be widespread. With increasing time since fire, efforts to restore these sites may be complicated by encroaching trees resistant to removal by fire alone and the difficulties of reintroducing low-intensity understorey fires where the flammable understorey has been lost through shading. Further research into the impacts of fire exclusion is urgently required, as is the reinstatement of fire to fire-excluded vegetation to prevent ongoing displacement of fire-dependent biodiversity values.