Pre-Dispersal Seed Losses, and the Survival of Seeds and Seedlings of Two Serotinous Banksia Shrubs in Burnt and Unburnt Heath

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Abstract
(1) We report on a field survey which compared pre-dispersal seed losses, and a field experiment which compared the survival of seeds and seedlings, in two co-occurring Banksia shrubs from a fire-prone heath. The obligate-seeder, B. ericifolia, is killed by fire whilst B. oblongifolia resprouts from a lignotuber. Both species are serotinous. (2) From 20 to 30% of the seed bank of each species was destroyed by insect larvae. However, in neither species did losses to seed predation increase over a series of stands last burnt between 5 and 24 years previously. Overall, a significantly lower percentage of B. ericifolia than of B. oblongifolia seed was eaten (21.6% vs. 28.2%). (3) A higher percentage of B. oblongifolia than B. ericifolia follicles opened and released their seeds without stimulation by fire (11.3% vs. 4.2%), and the percentage of open B. oblongifolia follicles increased linearly with time since burning. This may be one mechanism by which new B. oblongifolia individuals establish between fires. (4) Approximately the same proportion of seeds from both species survived when placed into unburnt vegetation, but more seeds survived under B. oblongifolia shrubs than under B. ericifolia in unburnt vegetation. However, the proportion surviving in both locations was small (13% vs. 10%). (5) There was no difference between species in seedling survivorship in unburnt vegetation under either adult shrub, nor was there any difference in the survivorship of B. oblongifolia and B. ericifolia seedlings in a recently burnt site. More seeds and seedlings of both species survived in the recently burned site than in all unburnt sites. (6) Selection for complete serotiny may be relaxed in species whose life histories include vegetative regrowth after fire. This may explain why chracteristically resprouting Banksia species release seeds in the absence of fire.