Canopy-Stored Seed Banks of Allocasuarina distyla and A. nana in Relation to Time Since Fire

Abstract

Aspects of the serotinous seed banks of Allocasuarina distyla (Vent.) L. Johnson and A. nana (Sieb. ex Spreng.) L. Johnson are presented in relation to fire. A. distyla is single-stemmed and fire-sensitive; A. nana resprouts multiple stems from a lignotuber following fire.

Vegetative above-ground plant growth correlates with seed bank size in A. distyla better than in A. nana. There is approximately 10 times the canopy-stored seed in A. nana 8 years after fire than in A. distyla 9 years after fire. The critical period to initial seed set in A. distyla is between about 7 and 9 years. In A. nana, this period is typically longer but appears to depend on the age of the seed-producing genets.

The age structure of the seed banks in both species remains more or less constant in time, with most seed being young. Seed viability declines in A. distyla from an initial 60% to less than 10% within about 12 years after seed set. A similar pattern appears likely for A. nana, although initial seed viability is about 40%. Attrition in seed viability is attributed to seed predation by insects, fungal attack and seed senescence. The dynamics of seed production and survivorship appear to be similar to those in serotinous proteaceous species studied to date.