Seed Banks, Fire Season, Safe Sites and Seedling Recruitment in Five Co-Occurring Banksia Species

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Abstract
The quantity of seed stored in the canopy of five co-occurring Banksia species varied by nearly two orders of magnitude. The three species which resprout vegetatively after fire, produced less seeds and retained smaller seed banks than the two non-sprouting species. Contiguous patches of scrub-heath were burned in spring and autumn. The spring fire was cooler than the autumn fire and both sets of seed released subsequently did not germinate until the following (common) winter. the rate of seed release was higher after the autumn fire than the spring fire. The non-sprouting species released more seeds after each fire and yielded more seedlings per parent than the resprouting species. Percentage (field) germination of the non-sprouters was not consistently different from that of the resprouters. Seeds exposed on the soil surface during summer soon lost viability compared with buried seeds. The large number of seedlings established up to eight months after the spring fire resulted from many seeds escaping exposure by dispersal into liter-covered ''safe'' sites. Although litter microsites covered only 30% of the ground surface after the spring burn, they accounted for 80% of the seedlings both before and after the summer drought. Litter microsites covered only 14% of the autumn-burned site but accounted for 60% of the seedlings before summer and 40% after summer, suggesting density-dependent thinning of seedlings. The autumn-burned site supported more than twice the density of seedlings than the spring-burned site and 65% in the autumn-burned site, equalizing the seedling:parent ratio at both sites. Net recruitment of one-year-old seedlings varied from 0 for two resprouters to over 100 per parent for a non-sprouter.