Seasonal occurrence of fire and availability of germinable seeds in Hakea sericea and Petrophile sessilis

Abstract

1 Although the season of fire occurrence is known to affect recruitment to plant populations, it has received little attention. This study investigated the dynamics of the canopy-stored seed banks of two Australian obligate seeder shrubs, Petrophile sessilis and Hakea sericea (Proteaceae), with the objective of determining the changes in viable seed supply over a year. 2 The total number of germinable seeds in the canopy, each month for 12 months during 1996-97, was estimated from separate measures of (i) pre-dispersal predation of fruits; (ii) seed predation of insect parasitoids; (iii) viability of intact seeds; and (iv) loss of seed viability following experimental heating. 3 The two species had very different seed bank dynamics throughout the year. The seed store of P. sessilis appeared to be being replaced annually, as seeds in the older fruits rapidly lost germinability and new fruits matured to replace them. For H. sericea, the seed store appeared to be accumulating each year, because older fruits retained a high level of germinability. 4 The study indicates that no one fire season will maximize the germinable seed release after fire for all species. Management strategies should therefore include varied seasons of prescribed burning to avoid compositional change and a decrease in diversity that may result from a single-season approach.