Paleofire patterns in Tasmania: postglacial and Holocene record of fire and vegetation from Cradle Mountain-Lake St. Clair National Park, Tasmania, Australia
Stahle, Laura Nicole
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On centennial to millennial timescales fire regimes are driven by climate changes, vegetation composition, and human activities. In this study, I reconstructed the vegetation and fire history of Cradle Mountain-Lake St Clair National Park in northwestern Tasmania, and linked vegetation changes to variations in the fire regime, large-scale climate patterns, and anthropogenic activity. Postglacial vegetation and fire dynamics were inferred from five high-resolution pollen and charcoal records from lakes in the montane and subalpine zones of the National Park. Watershed-scale reconstructions of fire and regional trends in vegetation composition were compared to independent records of past climate and the regional archeological record to assess long-term climate-vegetation-fire-human linkages. Pollen and charcoal data indicate that during late-glacial period, the vegetation was largely open and fires were rare. During the Pleistocene-Holocene transition, rainforest taxa and subalpine woody shrubs began to increase in abundance. In the early Holocene, a fire activity maximum occurred at the three lower elevation sites while biomass burning remained low at the higher sites. The elevational differences and basin characteristics likely resulted in climate-controlled differences in vegetation and fuel flammability. The high biomass burning in the early Holocene occurred during the warmest interval of the Holocene as recorded by regional paleoclimate proxy records. The mid-Holocene period featured a multi-millennial phase of cool, temperate rainforest dominance at all sites. The relatively wet conditions of the mid-Holocene likely allowed the rainforest to reach its maximum extent. The late Holocene marks a regional shift toward open sclerophyll woodland associated with increased climate variability and decreased precipitation. A large fire episode occurred at all five sites during this period and hastened the shift in compositional balance from rainforest to a mosaic of sclerophyll woodlands and shrublands, rainforests, buttongrass moorlands, and alpine vegetation. Overall, the vegetation became substantially more open in the late Holocene. The human-fire linkages in Cradle Mountain are tenuous. There is no clear evidence that fire regimes or vegetation were extensively modified by humans prior to European settlement. Climate was the primary driver of fire activity over millennial timescales as explained by the close relationship between charcoal and climate proxy data.