THE SIZE, DISTRIBUTION AND GERMINATION REQUIREMENTS OF THE SOIL-STORED SEED-BANK OF GREVILLEA-BARKLYANA (PROTEACEAE)

Fire-triggered release from seed dormancy is a characteristic of many Australian plant species. We investigated aspects of the seed-bank dyn amics and dormancy characteristics in seeds of Grevillea barklyana, an understorey shrub of coastal sclerophyll vegetation in the Jervis Bay Region on the south coast of New South Wales. We used two soil core s izes to compare the number and distribution of stored seeds in soil co res taken from underneath and outside the limits of plant canopies at three study sites. Core size did not affect the estimate of seed densi ty. No seeds were found outside the existing canopies. Even in under-c anopy samples, seed numbers were small. Mean seed densities were estim ated as 10.9, 14.1 and 4.3 seeds per (sic) for the three sites. A hier archical series of laboratory experiments was used to test the germina tion response of both fresh and soil-stored seeds. Likewise, we attemp ted to simulate 'natural' disturbance conditions in a glasshouse exper iment. Both laboratory and glasshouse experiments indicated polymorphi sm in germination behaviour. A constant proportion of seeds exhibited enforced dormancy, when moist at room temperature, while a smaller num ber of seeds showed either an induced dormancy or a non-seed-coat link ed innate dormancy. The majority (75%) of seeds were innately dormant due to a hard seed-coat. This dormancy was broken when the seed-coat w as damaged, for instance, by heat. The level of polymorphic germinatio n behaviour will be dependent on the length of the inter-fire periods. We conclude that the expression of polymorphism within and between sp ecies across a range of environments and fire regimes is an important consideration for any further study attempting to assess the role of t he seed-bank.