Seed Bank Dynamics of Three Co-Occurring Banksias in South Coastal Western Australia: the Role of Plant Age, Cockatoos, Senescence and Interfire Establishment.

Abstract

Seed bank dynamics of three co-occurring, non-sprouting Banksia species (B. baxteri, B. speciosa and B. coccinea) in patch-burnt scrub-heath (aged 10 and 21 years) were studied in the southern sandplains of Western Australia. In the younger plants, canopy seed storage was highest in B. coccinea. However, 21-year-old B. coccinea stored an order of magnitude fewer seeds than the other species and no more than young B. coccinea. Seed storage per year increased exponentially with plant age in B. speciosa and B. baxteri, whereas a quadratic function, peaking at 16 years, best described seed storage in B. Coccinea. Degree of serotiny was lowest in B. coccinea. Seed abortion did not vary between age cohorts but was highest in B. coccinea. Granivory ranged from 18 to 42% and was highest in the older plants and in B. baxteri. Cockatoos removed about 20% of cones in B. baxteri and B. coccinea and 10% in B. speciosa. Experimental cone removal accelerated follicle opening, especially in B. coccinea, irrespective of whether cones were placed on the ground (simulating cockatoo removal) or reattached to the plant (simulating plant death). Half the 21-year-old B. coccinea were dead and the remainder were considered senescent, as most branches showed dieback and cone fertility had fallen to 8%. Death of the other species was negligible, with cone fertility rising to a mean of 45% (B. speciosa) and 66% (B. baxteri). Interfire establishment was significant only in B. coccinea. The build-up of a viable seed bank with time occurred at a slower rate than for non-sprouting banksias in the northern sandplains.