PHENOLOGICAL TRENDS WITH LATITUDE IN THE MANGROVE TREE AVICENNIA-MARINA

Leaf fall and reproductive phenology of Avicennia marina using samples from 25 sites in Australia, Papua New Guinea and New Zealand revealed major trends with latitude. Flowering shifted from November-December in northern tropical sites, to May-June in southern temperate sites. Periods between flowering and fruiting increased from 2-3 months in tropical sites to 10 months in southernmost sites. Leaf fall was more variable with unimodal annual peaks in temperature sites and often multimodal patterns in the tropics. Initiation of the reproductive cycle probably occurred when daylength exceeded 12 h, followed by rates of development to flowering and fruit maturation given by a linear function of mean daily air temperature. This explained up to 92% of variance in total cycle duration and timing. Temperature affected reproductive development by increasing growth rates by a factor of 2 or 3 for each 10°C rise. Appearance of new leaves on canopy shoots near Townsville, N Queensland, had seasonal highs followed by peak falls a month later, and leaf longevity was c13 months. Inflorescence leaf appearance was predominant in low-moisture and low-temperature sites during early summer, and independent leaves appeared mostly in wetter tropical sites during winter months. Distributional limits of A. marina in higher latitudes coincide with trends towards zero reproductive success (notably seen in flowering), apparently brought about by a convergence of phenological events within the shorter growth period of summer in these latitudes. -from Author