Broadway Arboretum

Species Information Page

Banksia grandis Bull Banksia


Location in Arboretum: Southern Jarrah Forest
No on Map: SJF05

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  • Roots of a wide range of Proteaceous plant species exude carboxylates, e.g. citrate, into the rhizosphere (i.e. the zone around the roots), to mobilise sparingly available phosphate.  Banksia grandis forms `proteoid' or `cluster' roots, and exudes significant amounts of carboxylates (1). It has been suggested by some that the carboxylates helped create soils we have in the Darling Range.
  • A study in the Northern Jarrah Forest found that trees became reproductive at a mean diameter at breast height of 4.5 cm and successfully reproductive at a mean diameter at breast height of 6.7cm. Tress of diameter at breast height less than 10cm produce fewer fertile inflorescences (i.e. flowers) than trees of larger diameter at breast height.  Moderate intensity fire markedly reduces production of inflorescences for at least three flowering seasons.  Less than 2% of flowers on an average inflorescence set fruit, and only 1 to 5% of inflorescences develop into fertile inflorescences (i.e. generate fertile seed).  May be influenced by resources rather than insects (2).
  • The period for a Banksia grandis seedling to attain 1.3 m height was calculated as approximately 15 years. Watering, shading and spraying with insecticide had no significant influence on height growth of saplings. Four years after fire, sapling coppice from large lignotubers nearly attained the height of the plant before the fire. Trees, but not saplings, grew faster after logging of forest (4).
  • Removal from the forest floor of seed or fruit of the six commonest species of trees in upland areas of the northern jarrah forest of Western Australia was studied experimentally. The smallest seeds (Eucalyptus marginata, Allocasuarina fraseriana) were taken by insects (presumably ants). Heavier seeds or fruits (Corymbia calophylla, Banksia grandis, Persoonia longifolia, P. elliptica) were taken more often by vertebrates (presumably small mammals). Seeds of Corymbia calophylla and Banksia grandis were most preferred by vertebrates, possibly because they have the highest relative concentrations of nitrogen and phosphorus (3).
  • Dehiscence of follicles is caused by wetting and drying of the fruit, so that most seeds fall to the ground during autumn. Seeds are wind- dispersed, settling downward from the parent tree and 90% of seed falls within the first year (5).