Freezing resistance of New Zealand trees and shrubs

Twigs of 42 native woody species representing a temp.-related ecological gradient were collected in New Zealand in July (midwinter) and flown to Japan where they were artificially hardened and tested for freezing resistance. Resistance was well correlated with distribution: for leaves, resistance ranged from -3 deg C or warmer for broadleaved species not extending beyond 39 deg S. lat. to -18 deg C to -25 deg C for the hardiest shrubby subalpine conifers (in order of increasing resistance, Phyllocladus alpinus, Podocarpus nivalis and Dacrydium bidwillii). Agathis australiswas somewhat more resistant (-7 deg C) than its natural range would indicate. In tests on non-native southern hemisphere spp. grown at Christchurch, values were similar to those for natives, but the deciduous Nothofagus antarctica was much hardier (to -22 deg C) than the native evergreen N. solandri: (-10 to -15 deg C).