Climatic control of annual leaf area production in two New Zealand subalpine composite shrubs

The annual leaf area production of the subalpine composite shrubsOlearia ilicifolia andSenecio bennettii is related to the environmental temperatures experienced at the time of leaf primordia initiation in the previous growing season. The sensitive period occurs 3-9 weeks after bud break when the new resting bud is formed in the growing shoot apex. The initiation periods ofOlearia andSenecio do not coincide and, therefore, the annual variation of leaf area increment follows a different pattern in the two species. A minimum annual increment of 20 cm² inOlearia and 40-45 cm² inSenecio seems to represent a probable lower limit; lower temperatures are unlikely to be experienced during primordia formation as these would delay bud break.