A Trade-off between Fecundity and Drought Susceptibility in Adults and Seedlings of Hakea Species as Influenced by Leaf Morphology

Abstract

Successful seedling recruitment is vital for the persistence of fire-killed species in a community. Maximising seed and seedling production (fecundity) and the ability of adults and seedlings to survive summer drought are crucial in taking advantage of post-fire recruitment opportunities. In this study, the fecundity (seed and seedling production), mortality and water relations of fire-killed Hakea species with contrasting leaf morphologies (broad and terete) were examined over 2 consecutive years of exceptionally low rainfall at two sites, to investigate possible trade-offs between drought susceptibility (as influenced by leaf morphology) and fecundity of a species. Adult mortality was high in the broad-leaved species (H. smilacifolia Meissn. and H. undulata R.Br.) and low in terete-leaved species (H. erinacea Meissn., H. circumalata Meissn. and H. polyanthema Diels) with high transpiration rates (broad-leaved species) associated with greater plant death. Only H. smilacifolia had proportionally greater fecundity to compensate for high adult mortality. Seedling mortality increased proportionally with higher initial seedling : parent ratios (adult fecundity). Lowest mortality was for the terete-leaved species, apparently achieved by means of a combination of drought avoidance and tolerance mechanisms. Hakea undulata seedlings had the highest mean leaf area, but mortality was highest in H. smilacifolia. Thus, for seedlings, leaf morphology was not as strongly related to drought susceptibility as it was for adults.