Frost Hardiness of Subalpine Eucalypts in Britain

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Abstract
Laboratory freezing tests were used to determine seasonal changes in the frost hardiness of detached shoots of young trees of Eucalyptus gunnii (from central Tasmania), and E. niphophila and E. debeuzevillei (‘snow gums’ from the Snowy Mountains, Australian Capital Territory). The trees were growing at the Bush Estate. No difference was found between the species or between seedlots, all of which were from high altitudes near the tree line. In midwinter (February) the shoots tolerated −16°C without suffering damage, and many shoots survived temperatures as low as −18°C to −22°C. This result agreed with Evans' (1986) observation that some trees within these seedlots survived temperatures in the range −19°C to −23°C in field planting during the winter 1981/82. In their native habitats the trees rarely experience temperatures below −20°C. The shoots did not harden appreciably before they experienced frosts (in late October/early November) and so may be prone to autumn frost damage. By contrast, they were slow to deharden in late winter and spring and did not seem prone to spring frost damage. There were no killing air frosts during the period of this study (winter 1985/6), but many trees died, possibly as a result of ground freezing, producing root injury and/or shoot desiccation. In subalpine regions of Tasmania and the Snowy Mountains the ground is covered by snow throughout the winter. Variation in frost hardiness within these hardy seedlots could be exploited.

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