Fire history influences reproduction in congeneric food tree species with contrasting post-fire reproductive strategies

Felicity Eloise Charles , April E Reside, Patrick T Moss, Annabel L Smith

In fire-prone regions globally, plants have developed reproductive strategies enabling population persistence under historical fire regimes. However, many common plant species are threatened by a mismatch between historical and contemporary fire regimes, which also threatens animal species relying on them for resource provision. We investigated how recent fire history affected reproductive trait variation in two congeneric food tree species (Casuarinaceae) for the threatened Glossy black-cockatoo (Calyptorhynchus lathami, Cacatuidae): Allocasuarina littoralis (an obligate seeder) and A. torulosa (a facultative resprouter). Lab-based germination experiments measured germination responses of seeds exposed to heat shocks of 80° and 95°C, smoke, and combinations of these treatments. Field-based surveys measured demographic structure and reproductive output. Heat and smoke treatments slowed germination in A. torulosa but had no effect on germination in A. littoralis. Germination rate increased with seed weight but was unaffected by heat and smoke. Heavier seeds were associated with higher fire frequencies and greater temperature variability at seed collection sites. In A. torulosa, heavier seeds took longer to germinate, especially when seeds were collected from frequently burnt sites, possibly reflecting a resprouting-seed production trade-off. Fire history did not influence reproductive output or population demographic structure for either species. For restoration, heat and smoke treatments are unlikely to be necessary once seeds are released from cones. However, local fire history and seed weight should be considered when collecting seeds for restoration programs. Differences in species post-fire establishment driven by variation in germination response to fire of Allocasuarina could influence a dietary specialist threatened cockatoo.