Spatial and temporal variation in litter fall of Avicennia marina (Forssk.) Vierh. in the Brisbane River, Queensland, Australia

Abstract

Leaf, woody and reproductive litter fall in a sub-tropical stand of Avicennia marina (Forssk.) Vierh. was measured monthly, along four transects (two in mature forest, two in regrowth) at three tidal inundation levels, for 2 years to investigate the spatial patterns of litter fall in relation to position on the shore and vegetation maturity. Litter fall in 1992/1993 was 831.3 g dry weight (DW) m −2 year −1 and in 1993/1994, 921.7 g DW m −2 year −1. Over the 2 year period, leaf litter fall accounted for 47% of total litter fall, reproductive litter 30% and woody litter 23%. Leaf fall was seasonal with a maximum in the wet summer season; wood fall was aseasonal but positively correlated with periods of high wind. Reproduction was biennial with fruit fall in the dry winter season. Litter fall was consistently higher at the mid tidal level and decreased up- and down-shore from this point. Rates of litter fall were independent of the maturity of the stand and tree density but organic cycling was much slower in the mature forest. Larger trees produced more fruit, but fruit production per unit of tree biomass was greater in smaller trees.