Abstract
The Tasmanian Wilderness World Heritage Area (TWWHA) has globally significant natural and cultural values, some of which are dependent on the absence of fire or the presence of particular fire regimes. Planned burning is currently used to reduce the risk of loss of world heritage values from unplanned fires, but large and damaging fires still occur, with lightning as the primary ignition source. Lightning-caused fire was rare in the TWWHA before 2000. There has since been an increase in both the number of fires following lightning storms and the area burnt by these fires. In the absence of a direct measurement of lightning strike incidence, we tested whether changes in rainfall, soil dryness and fuel load were responsible for these changes in fire incidence and extent. There were no relationships between these variables and the incidence of fires associated with lightning, but the variability in the Soil Dryness Index and the mean of 25% of driest values did predict both the number and area of fires. Thus, it appears that an increase in the proportion of lightning strikes that occur in dry conditions has increased ignition efficiency. These changes have important implications for the management of the TWWHA’s values, as higher projected fuel loads and drier climates could result in a further increase in the number of fires associated with lightning.
Highlights
The Tasmanian Wilderness World Heritage Area (TWWHA) has been listed by the World HeritageCommittee for its globally significant natural and cultural values [1]
Increases in lightning activity due to climate change have been observed across the globe or are projected to occur across the globe [10,16,22,23,24,25], with lightning strike rate correlated with temperature on short time scales [10]
It is possible that the increase in lightning fires observed in the TWWHA since the 1990s may be the result of an increase in dry lightning strikes, an increase in the overall amount of lightning, an increase in fuel dryness, an increase in the fuel load, or a combination of all four factors
Summary
Committee for its globally significant natural and cultural values [1]. The TWWHA encompasses areas of great natural beauty, has globally significant Aboriginal cultural heritage and conserves globally significant geodiversity and biodiversity [2]. The globally significant palaeoendemic plants of the TWWHA are concentrated in places where fire has been rare or absent [3]. Fire-intolerant plant communities sit within a matrix of globally significant moorland vegetation, which is dependent on frequent fire to maintain species richness and structural diversity [4]. Frequent low-intensity prehistoric anthropogenic fire in moorlands both maintained pyrophilic moorlands and protected pyrophobic vegetation. Prehistoric fires in pyrophobic rainforests, subalpine and alpine areas were likely to have been the result of natural ignition and/or escapes [5,6,7]
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