Freezing Resistance of Trees of the South Temperate Zone, Especially Subalpine Species of Australasia

Abstract

Maximal resistance to winter freezing of trees of the South Temperate Zone, especially subalpine trees of Australasia, was assessed. Most of the tree species which grow in lower altitudes were marginally hardy to -I 0°. Subalpine and alpine shrubby species such as Podocarpus nivalis, P. lawrencei and Dacrydium bidwillii were the hardiest conifers in New Zealand and Australia, resisting freezing to -20° to -23°. This hardiness was comparable to that of conifers native to the warm temperate or temperate parts of Japan. In Nothofagus, the deciduous, subalpine N. antarctica of South America was the hardiest, resisting freezing at -22°. A New Zealand evergreen timberline species, N. solandri var. cliffortioides was marginally hardy to -15°. Of the Eucalyptus species, E. paucijlora which forms the alpine tree limit on the mainland of Australia was the hardiest, resisting freezing to -15° in the leaves. Other high-altitude angiosperm species tested mostly survived freezing to only -10° or -15°.Very hardy tree species that withstand freezing below -30° seem not to have evolved in the Southern Hemisphere, because the mild, oceanic winters did not provide the stimulus, and because hardy northern tree genera, with minor exceptions, have been unable to cross the barrier formed by the tropics.

Seasonal frost tolerance of some ornamental, indigenous New Zealand plant species in the generaAstelia, Dicksonia, Leptospermum, Metrosideros, Phormium, Pittosporum, andSophora

“…In general, within the range of species and cultivars evaluated, these data support the findings of Sakai et al (1981) that very hardy tree species do not appear to have evolved in Australasia. Unlike the winter-cold, continental climates of North America and Eurasia, the mild oceanic winters of Australasia have not led to the natural selection of very hardy trees and shrubs.…”

Seasonal frost hardiness ofNothofagus solandriseedlings from two altitudinally diverse sites in Canterbury, New Zealand

“…The results of this study and those of Wardle & Campbell (1976), Sakai & Wardle (1978) and Sakai et al (1981) suggest that the mid-winter frost hardiness ofNothofagus solandri seedlings increases with increasing altitude, although there may be a maximum limit of about -140C to the amount of frost hardiness that can be developed in mountain beech seedlings. A similar increase in frost hardiness forAbies sachalinensis growing from 300 to 1200 m in Hokkaido has been shown by Eiga & Sakai (1984).…”

“…Sakai et al (1981) have previously shown in detached twigs that the leaves of mountain beech trees at 1370 m on Craigieburn could tolerate-13~ while at 910 m at Arthur' s Pass, leaves could tolerate-10~ Similarly, Wardle & Campbell (1976) and Sakai & Wardle (1978) have shown that mountain beech trees at other North Canterbury sites can tolerate between -10 and -13~ in mid-winter. Allowing for both climatic differences during the year of study and the different techniques to assess frost hardiness, there is close agreement between these studies on the maximum frost hardiness of both seedlings and mature mountain beech trees confirming that age apparently does not affect frost hardiness.…”

Elevated atmospheric [CO2] promotes frost damage in evergreen tree seedlings

“…This species is one of the most freeze tolerant of eucalypts (Sakai, Paton & Wardle 1981) and withstands temperatures as low as -18°C when fully cold hardened (Harwood 1981). In mid-spring, there was a 23 d period when the minimum temperature averaged + 2°C at seedling height and decreased below zero to -2°C on one night.…”