An examination of the drought and frost tolerance of Banksia marginata (Proteaceae) as an explanation of its current widespread occurrence in Tasmania

Populations of Banksia marginata Cavanilles from sea level to 1040 m above sea level near Hobart were examined for frost and drought tolerance to determine the extent of the inter-population variation and physiological plasticity of this species. This study was designed to give some insight into the reasons behind the successful occupation of a wide range of habitats by B. marginata in Tasmania today. All populations were highly frost tolerant, irrespective of season, with the peak tolerance usually occurring in summer, suggesting a link to some other physiological aspect such as drought tolerance. Water relations results were complex and highly variable among the populations. For the highest altitude population at least it is probable that cell elasticity and high apoplastic water contents, rather than osmotic adjustment, assist in frost and drought tolerance. It is likely that the physiological plasticity and apparent genetic diversity exhibited by these populations assisted the survival of B. marginata in pockets of refugia throughout Tasmania during past climatic upheavals during glacial and interglacial cycles.