REPRODUCTIVE ECOLOGY OF BANKSIA GRANDIS (PROTEACEAE)

Abstract

The reproductive characteristics of Banksia grandis Willd. were studied in the northern jarrah forest of Western Australia. Most flowering occurs in November, with maturation of fertile (seed‐bearing) infructescences taking about 12 to 14 months. Number of inflorescences produced by a tree is not closely related to its diameter at breast height (DBH). Trees become reproductive at mean DBH of 4–5 cm and fruit successfully at mean DBH of 6.7 cm. Trees of DBH < 10 cm produce fewer fertile infructescences than trees of larger DBH. 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 infructescences. The cause of the latter was investigated experimentally. Although insect larvae (Lepidoptera, Coleoptera) damage infructescences, inflorescences sprayed with insecticide do not develop differently from those not so treated. Insect damage is least in inflorescences produced in late November and early December but there is no corresponding increase in development of fertile infructescences. Ants do not protect inflorescences from insect damage and insects are of little significance as predators of seed within the follicle. Whether fruit development is limited by pollination could not be adequately assessed. Low fruit set in B. grandis may result from shortage of resources, with many flowers and inflorescences allowing B. grandis the option of setting large numbers of fruits should favourable conditions prevail. Copyright © 1985, Wiley Blackwell. All rights reserved