Seed bank dynamics of a serotinus, fire-sensitive Banksia species

Abstract

Banksia burdettii is a locally abundant shrub restricted to a small area in south-western Australia. At the study site, the canopy-stored seed bank built up exponentially with plant age to yield a mean of 830 viable seeds per plant from about 212 000 ovules produced over 16 years. Seed availability was the net result per year of number of flower heads, extent of head removal by cockatoos, number of florets per head and number of fruits (follicles) per floret in the production phase and the extent of seed abortion, insect granivory, seed senescence and spontaneous seed release in the mortality phase. Plants are killed by fire and a substantial proportion of cones was consumed by a hot fire. Up to 87% of viable seed may survive and be released within 100 days of a fire, depending on intensity and season of burn. Plants which died in the absence of fire released little viable seed subsequently, while the remainder were consumed when fire occurred. Comparison of 25 reproductive attributes between B. burdettii and another two Banksia species occurring in the vicinity indicated that it has much in common with these serotinous, non-sprouters. Although viable canopy-stored seeds account for few of the original ovules, reproductive inefficiency, once a fire interval of 10 years is exceeded, cannot explain the restricted distribution of this species.