W Harris; RE Beever; BM Smallfield
Winter cold damage in 1996 and 1997 was recorded for 28 populations of Cordyline australis from a wide latitudinal range in New Zealand and single populations of C. banksii and C. indivisa grown in field experiments at Lincoln and Invermay, New Zealand. Damage to a single plant of C. obtecta grown at Lincoln was also recorded. Cordyline banksii and were damaged the most by freezing. Levels of cold damage to were closely related to latitude of origin; populations from northern North Island suffered severe damage whereas those from inland southern South Island showed little damage. These relationships were clearest when the populations were exposed to the lowest grass minimum temperature of -9.7[[ring]]C that occurred at Invermay in winter 1996. Retardation of the height growth of the populations most severely damaged in winter 1996 kept them in the frost layer in winter 1997, increasing their exposure to further damage. Variation in cold damage that related to altitude and topography of the sites of origin was also indicated. Damage to shoot apices by freezing temperatures at Invermay in 1996 induced plants of northern populations to form multiple shoots. The results suggest that there has been strong natural selection matching the cold tolerance of seedlings of C. australis populations to minimum temperature regimes at their sites of origin. The results are relevant to the sourcing of plants for restoration of native vegetation and to horticultural use of C. australis.