Seed Production and Mortality in a Rare Banksia Species

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Abstract
(1) Seed production and release by Banksia tricuspis, a small tree restricted to a 50 km2 area in south-western Australia, were assessed. Most plants in the study population flowered in the nineteenth year after fire and on average 16,500 ovules per adult were produced. (2) Most flower heads were destroyed by moth larvae and larval-seeking cockatoos. Of the 115 young seeds produced on average per adult, almost half aborted, apparently due to the constraints of the breeding system and limited supply of mineral nutrients. Beetle larvae destroyed a further 15% of mature seeds. (3) There was marked senescence and spontaneous release of seeds in the fourth and subsequent years. The mean value of eighty-four canopy-stored viable seeds per adult that remained were almost entirely accounted for by the size of the crops for the last 3 years. (4) All viable seeds were released in response to an autumn wildfire. Seedling establishment only occurred immediately after the fire. (5) Low seed production and rapid depletion of the canopy-stored seed bank are not sufficient in themselves to account for the rarity of B. tricuspis. Management in the wild should include conservation of cockatoos and other animals which consume the granivorous moth larvae and control of the fire regime.