W Harris; RE Beever; SL Parkes; T McSeveny
The retention of dead leaves covering the trunks of 8-year-old trees of Cordyline australis (cabbage tree, ti kouka) was significantly different between 28 wild populations from a 12° latitudinal range in New Zealand when grown under uniform garden conditions at Mt Albert, Auckland (36°53′S, 174°43′E) and Lincoln, Canterbury (43°38′S, 172°29′E). Particularly at Lincoln, trees of populations originating from south of latitude 38°45′ mostly had trunks fully covered by dead leaves at the time of observation. Temperatures recorded at Lincoln at heights of 1.40 m and 0.05 m showed that chilling on the trunk surface was reduced by a cover of dead leaves, particularly at 0.05 m during radiation frosts. This effect was separated from the shelter effect of the green leaf tufts of trees and shelter between trees in the experimental plantation. The adaptive function of the retention of dead leaves on the trunk of C. australis in frost-prone locations in southern New Zealand is considered with reference to other possible adaptive functions.