a1 CSIRO Division of Entomology, Tropical Ecosystems Research Centre, PMB 44, Winnellie, N.T., Australia 5789
An investigation of seasonal changes in litterfall in a dense stand of the invasive tropical shrub Mimosa pigra was carried out in northern Australia between October 1984 and December 1986. Total annual litterfall averaged 758 g m−2, close to the value predicted for the latitude and altitude of the site. Leaf litter formed 56.6% of this total, woody material 22.7%, and reproductive material 20.7%. Total litterfall was strongly seasonal, at a maximum in the late wet season or early dry season, and at a minimum late in the dry season. A broadly similar pattern was shown by the various components of the litter, except for woody litterfall, which followed no strong seasonal trend. Variation in the amount of available soil moisture, as calculated from a simple water balance model, accounted for much of the variation in the components of litterfall.
The proportion of all initiated flower heads which produce seeds was estimated to be between 2.1 and 4.5%. The mean annual seed fall was 9103 m−2, nearly two orders of magnitude higher than most native shrub populations, and it is argued that this is partly a result of the absence of natural enemies in the introduced range.
(Accepted October 20 1987)