Invasion by Pittosporum undulatum of the Forests of Central Victoria. II. Dispersal, Germination and Establishment

Abstract

Invading Pittosporum undulaturn tends to be clumped around the butts of established trees. This is due to the preferential deposition of seeds in these sites by the European blackbird (Turdus merula) which is believed to be the main vector of dispersal. Native silvereyes (Zosterops lateralis) eat some seed but are not considered important in dispersal. The high mortality of seedlings in exposedsites reinforces the patchy pattern originally dictated by seed dispersal. Seeds may germinate after seed fall in spring but most seeds germinate in autumn. No seeds germinate during summer because of the low rainfall and high temperatures, the optimum germination temperature being 18-21°C . After 16 months' storage at moderate temperatures and humidities, 80% of seed was still viable but viability was reduced to 30% at very low humidities. Seedlings of P. undulatum have three growth stages. The juvenile and transitional stages last 6-12 months and have alternate leaves. In the adult phase a terminal vegetative bud forms at the stem apex. Bud burst may occur several times a year in seedlings and twice a year in fruiting adults. The seedling root habit varies with soil type. The seedlings are able to coppice if the shoot is removed P. undulatum is an aggressive invader of eucalypt forests despite the poor survival of the initial colonizers. The formation of a regeneration niche ensures the survival of succeeding generations. Consequently, P. undulatum is a permanent threat to the Victorian vegetation.