The Influence of Hardening and Waterlogging on the Frost Resistance of Subalpine Eucalypts.

Abstract

Marked interspecific differences in frost resistance were shown to exist between eucalypt seedlings grown in reciprocal field transplant trials conducted at a frost hollow on Snug Plains, south-eastern Tasmania. Populations of the six eucalypt species tested naturally inhabited the margins and base of this frost hollow. A growing season frost of - 5.5°C caused substantial damage to E. delegatensis, E. pulchella, E. urnigera, E. johnstonii and E. coccifera but only slight damage to E. gunnii. A winter frost of - 10.5°C caused markedly less damage than the growing season frost, suggesting that appreciable hardening occurs in winter and that growing season frosts may play a significant role in determining the distribution of subalpine eucalypts. E. pulchella appeared more resistant to growing season frosts than E. delegatensis while the reverse occurred in all but one of the experimental gardens during winter frosts. The reasons for this reversal and its significance are discussed. Frost chamber experiments confirmed the major differences between species in frost resistance and the importance of hardening. The reciprocal transplant trials suggested that seedlings from subgenus Symphyomyrtus were more frost resistant than those from subgenus Monocalyptus in sites prone to waterlogging. This was sup- ported by frost chamber trials in which a significant interaction between frost resistance and waterlog- ging was demonstrated. Species from subgenus Monocalyptus showed a reduced ability to harden under waterlogged conditions compared with species from subgenus Symphyomyrtus. This interaction may be of ecological importance since species from subgenus Monocalyptus do not occur in cold, waterlogged sites at Snug Plains. The present and previous experiments suggest that the distribution of subalpine eucalypts is dependent upon the interaction of a range of factors including the severity of winter frosts, resistance to growing season frosts, the suitability of the site for frost hardening and the degree of waterlogging.

Frost damage to eucalypts in a short-rotation forestry trial in Cumbria (England)

“…Of seven species of eucalypts, E. nitens was found to be the poorest in terms of cold tolerance, with E. gunnii being fourth out of the seven species. This contradicts other work that suggests E. gunnii is particularly cold-tolerant (Davidson & Reid 1987).…”

“…It is E. gunnii that inhabits a colder alpine environment in Tasmania, compared with the montane, lower latitude areas occupied by E. nitens on the main portion of Australia. E. gunnii is noted as being iForest (2014) (Davidson & Reid 1987). This is supported by results from this trial; by the end of January, E. nitens had suffered significantly worse damage then E. gunnii from the cold (Fig.…”

“…Rapid growth is important, as larger trees have greater sap reserves and once trees reach 2-6 m the sensitive growing tips are usually above mild growing season radiation frosts (Davidson & Reid 1987). Furthermore, larger trees exhibit greater physiological maturity and tolerance to environmental stresses than smaller trees of the same age.…”

“…Harwood (1980, in King & Ball 1998 describes the importance of hardening, noting that there is little difference in frost resistance between subalpine species of eucalypts when they are in an unhardened state, yet when hardened they exhibit considerable variation. In sub-alpine eucalypts hardening is initiated through low temperatures, rather than reduced photoperiod (Eldridge 1969, in Almeira et al 1994; the crucial temperature for initiating hardening being between 2 °C (Paton 1983) and 4 °C (Davidson & Reid 1987). However, both the level and duration of cold is important to the hardening process and it is a characteristic only of those eucalypts from colder climates (Scarascia-Mugnozza et al 1989).…”

The Miena cider gum, Eucalyptus gunnii subsp. divaricata (Myrtaceae): a taxon in rapid decline

“…divaricata is a woodland tree adapted to the edges of treeless flats and hollows (often termed "frost hollows") in the general vicinity of Great Lake on the Central Plateau, Tasmania (Jackson 1973, Kirkpatrick & Gibson 1998. These sites tend to be poorly drained, and exposed to the early morning sun, both of which may accentuate the damaging effects of frost (Davidson & Reid 1987, Close et al 2001. Nevertheless, in winter, these sites tend to be covered by cloud and mist; the ability of E. gunnii sens.…”