Seedling Recruitment Strategies in Obligate-Seeding and Resprouting Banksia Shrubs

Banksia ericifolia is killed by fire and so depends upon seeds for persistence. In contrast, B. oblongifolia can persist after fire by resprouting from protected buds, as well as by recruiting seedlings. These serotinous species coexist in the fire-prone scrublands of the Sydney Basin. Here we report experiments that compared seed release from cones retained in the canopy, seed germination, and seedling establishment in these two species. B. oblongifolia seeds were released more quickly than B. ericifolia seeds after a fire, and B. oblongifolia follicles opened and shed seeds after exposure to lower temperatures than those of B. ericifolia. B. oblongifolia seeds germinated more quickly than those of B. ericifolia. The relative growth rates and leaf mass ratios (mean ratio of leaf dry mass to plant dry mass over sequential harvests) of the two species did not differ. Root : shoot ratios were significantly large and biomass allocation to roots was faster in B. oblongifolia seedlings. B. ericifolia seedlings survived low and intermediate levels of droughting better than B. oblongifolia under greenhouse conditions. In a field experiment in which water was not limiting, large B. oblongifolia seedlings had the highest survival rate. These results suggest that selection has acted on B. ericifolia to minimize the chance of zero seedling survival by distributing the risks over more than one germination episode. There was no consistent evidence to support the hypothesis that selection on this species has increased its probability of seedling survival during any one germination opportunity relative to its congener.