Phenology, seed ecology, and age structure of Spanish heath (Erica lusitanica) in Canterbury, New Zealand

Abstract

Seasonal growth patterns and phenology of Spanish heath (Erica lusitanica Rud. in Schrad.) were studied at several sites in Canterbury, South Island. Shoot growth begins very early in spring but is affected by frosts above 400 m a.s.l. and by drought at lower altitudes. Flower buds are formed in autumn, flowering is in spring, and mature seed is produced early in summer. A typical 4–6 year-old bush with c. 20 branches produces c. 9 million seeds annually. Seed germination is highest under fluctuating temperatures and in full light, but 42% to 75% of seeds are dormant. These become incorporated in the soil seed bank, mostly in the upper few centimetres where they can survive for at least 4 years and possibly much longer. The highest number of buried seeds, 480,000 m⁻², was found beneath dense heath scrub and 1500 m⁻² are present up to 30 m beyond isolated heath clumps. Fire stimulates a small proportion of buried seeds to germinate. The distribution and age structure of heath clumps shows that heath is still expanding in the Geraldine area. The ability of heath to resprout after fire or damage and to produce seeds with the capacity for dormancy help to ensure its persistence on the landscape after the native shrub, Leptospermum scoparium, with which it is frequently associated, has disappeared.