Seed production and dispersal

In rainforests, seed production occurs throughout the year but peaks in the wet season. In north-eastern Australia, this peak in fruit production occurs between August and April (Hopkins and Graham, 1989). In the rainforest patches in the NT, the peak is more distinct and occurs in December, while fruit production was low in May and June (Price, 2004). Many species have episodes of very high seed production (i.e. masts), with large seed crops produced every 2-6 years (Hopkins et al., 1990; Connell and Green, 2000).

Many rainforest species have vertebrate-dispersed seeds. In the north-eastern Australian rainforest 83-93% of the tree species have bird-dispersed seeds (Hopkins et al., 1990). Cassowary (Casuarius casuarius) dung in north Queensland rainforest was found to contain diaspores of 78 plant species and germination was observed for 70 species. The success of germination was variable, with 397 of the 400 recovered Beilschmiedia oligandra LS Sm. seeds germinating, but only 6 of 1851 Elaeocarpus foveolatus F. Muell. seeds germinating (Stocker and Irvine, 1983). Dispersal of seeds by birds and flying foxes (i.e. large bats) is important for maintaining genetic diversity in the small patches. White et al. (2004) investigated seed dispersal into revegetated patches of rainforest and found much higher numbers of native species (in higher densities) dispersed by flying fauna, ground-dwelling mammals and wind to the adjacent site than to sites that were 600 m or 2 km away.

At least two tropical species are long-lived and semelparous. The palm Corypha elata Roxb. can grow 20 m tall with a 1 m diameter trunk before it flowers and then dies (Brock, 2001). Bambusa arnhemica F. Muell. is an arborescent, clumping bamboo that is endemic to riparian vegetation in the northern part of NT. It has an estimated lifespan of 40-50 years after which it flowers gregariously in clumps that range in size from a few hectares to several kilometres across, and then dies (Franklin, 2004).

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