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Seventy-five years of vegetation change after fire in Tasmanian alpine heathland

Ellen-Rose Sorensen, James Kirkpatrick

Abstract

Context. Alpine ecosystems are threatened by warming and an associated increase in fire frequency. There is a gap in our knowledge of succession in Tasmanian alpine heath after more than 50 years after fire. The literature suggest that the alpine successional progression usually involves decreasing rates of change;, decreasing differences between fire ages; ongoing transitions between shrub species; ongoing transitions from some life forms/species to others; and that warming results in increases in species richness. Aims. We test the hypotheses that there have been decreasing rates of change; decreasing differences between fire ages; ongoing transitions between shrub species; ongoing transitions from some life forms/species to others; and increases in species richness.We test for these tendencies after half a centuryto 75 years from fire in alpine vegetation on kunanyi (Mt Wellington) Tasmania, Australia. Methods. We documented the changes in vegetation structure and composition between 1998 and 2022 in plots on either side of an alpine fire boundary in the alpine heathland on kunanyi/Mount Wellington in Tasmania, and used earlier data and observations to extend the record of change after fire to 75 years. We put these changes in the context of the only small area of alpine vegetation that was not been burned in 1947 or later. Key results. The area last burnt in 1947 exhibited declines in all life form covers between 1998 and 2022. All lifeforms except tall shrubs and mat shrubs declined in cover in the area last burnt in 1962. By 2022, shrub cover in the 1962 burn had not attained equivalence with the area last burned in 1947. Herbs had the most dramatic decline in both fire age classes. There were few shrub seedlings in 2022. All but six taxa, three exotic, were observed in both the plots and previous broader surveys. Increases in species richness caused by the upward migration of lower-elevation species was not observed. The long-unburned patch lacked the major dominant of the 1947 burn plots, Orites acicularis, and was dominated by a gymnosperm absent from most of the mountain. Conclusions. Succession follows the initial floristic composition model. The differences in trajectories from the 1947 and 1962 fires could possibly be due to desiccation or abrasion damage from increasing wind speeds and temperatures. There are strong indications of further potential change in the absence of fire. Implications. The slow rate of recovery and its on-going nature emphasises the importance of keeping fire out of this vegetation type.

BT23069  Accepted 17 April 2024

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