Vegetative and reproductive phenologies of four mangrove species from northern Australia

Abstract

Mangrove communities in the tropical north of Australia are some of the most species rich in the world, yet surprisingly little is known of their reproductive and vegetative phenology. This study investigated the phenology of four mangrove species: Avicennia marina (Forsk.) Vierh., Ceriops australis (C.T.White) Ballment, T.J.Sm & Stoddart, Rhizophora stylosa Griff. and Sonneratia alba J.Smith, in Darwin Harbour over 24 months. Investigations included documenting the flowering and fruiting phenology, periods of leaf flush and leaf longevity. Flowering in these mangroves generally occurred during the dry season (June–October), with the exception of R. stylosa in which flowering occurred in the middle of the wet (December–February). Fruits and propagules were released in the dry and ‘build up’ periods (August–November), with the exception of A. marina, which released propagules in the middle of the wet season. Fruit and/or propagule maturation took less than 2 months in A. marina and S. alba, whereas in C. australis and R. stylosa maturation took 12 and 11 months, respectively. Timing of new leaf production generally coincided with the wet season, after the flowering and fruiting periods of each of the four species. Periods of leaf flush and leaf fall were often closely linked, and species with longer-lived leaves produced fewer leaves at each period of leaf flush. Maximum leaf longevity varied considerably among mangroves, ranging from 8 months in the lower canopy of S. alba to more than 24 months in C. australis. There was also large variability in leaf longevity among different regions of the canopy, with shade leaves generally living longer than sun leaves, and leaves in the upper canopy (3–7 m) longer than those in the lower regions (0–3 m).