School of Botany - Theses
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ItemClimate change and trajectories of vegetation change in an alpine heathland( 2014)Global warming is predicted to have substantial effects on vegetation dynamics in mountainous and high latitude ecosystems worldwide. In order to predict plausible trajectories of future vegetation change, we must first determine how temperature influences rates and directions of potential changes. Furthermore, we must quantify how these rates are influenced by disturbance and biotic interactions and how these may interact with climate. We also require detailed knowledge about how these interactive effects are likely to influence the establishment, growth and survival of seedlings; a life stage to which vegetation dynamics are sensitive and one which is highly vulnerable to changes in climate, disturbance and biotic interactions. In this thesis, I examine these issues in open heathland on the Bogong High Plains, Victoria, Australia. Using data derived from a combination of long-term monitoring, field and experimental studies I (1) demonstrate how one may model rates of vegetation change; (2) show how higher temperatures interact with climate-mediated disturbance, and biotic conditions to influence these rates; (3) determine how these effects are likely to influence vegetation change in alpine heathland under future climate and burned and unburned conditions. I then focused on examining how shrub dynamics may change under global warming. Specifically I determine: (1) How fire, elevation, adult density and topographic wetness influence shrub seedling establishment; (2) whether warmer post-fire conditions influence rates of seedling growth and mortality; (3) whether experimental growth responses are validated along by field surveys; (4) whether the proximity to Poa hiemata (the dominant grassland species) influences shrub seedling growth and mortality rates; and (5) whether Poa effects are altered by warmer conditions. I then synthesise all this information to examine whether global warming is likely to strengthen an existing feedback loop between shrubs and fire. I found that warming affected rates of life form cover change by altering post-fire regeneration and by reducing negative effects of competing life forms. In terms of shrubs, I found that fire increased shrub seedling establishment by more than 20-fold. Experimental warming of 1.2°C doubled seedling growth rates and increased survival. Warming also changed tussock grass interactions from facilitative to competitive. The consequences of these changes suggest that global warming will strengthen an existing feedback loop leading to changes in vegetation and fire regimes.