Influence of fire history on reproductive traits in a congeneric obligate seeder and facultative resprouter tree species

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

In fire-prone regions globally, evolution of plant traits that confer resilience to historical fire regimes is widespread. However, many common plant species are currently declining due to a mismatch between historical and contemporary fire regimes. These changes threaten long term community trajectories of plants and the animal species relying on them for food or habitat. Understanding plant responses to fire at critical life stages is needed to improve conservation of plant-animal interactions. We investigated how fire history affected reproductive traits (i.e., proportion germination, time to 50% germination, reproductive output, population age structure) relevant to critical life history stages of Allocasuarina littoralis and A. torulosa (Casuarinaceae). In southeast Queensland, Australia, these species are primary food trees of the nationally vulnerable Glossy black-cockatoo (Calyptorhynchus lathami, Cacatuidae). For both species, fire-cues (heat and smoke) did not increase the proportion of seed germinated, but proportion germination increased with seed weight. Heavier seeds were associated with exposure to more extreme environments such as environments with higher fire frequencies and temperature variability. In A. torulosa, seed weight generally increased germination time, except when seeds were collected from frequently burned sites which could be linked to a trade-off between resprouting and seed production. Heat and smoke slowed germination of A. torulosa (recorded as time to 50% germination) but had no effect on A. littoralis. Fire history did not influence reproductive output or population age structure in either species, but reproductive output was greater in sites with more woody vegetation cover, potentially reflecting greater establishment success. For restoration, our results indicate that fire is not necessary for successful germination in A. littoralis or A. torulosa, but when collecting seeds the local fire history and seed weight should be considered, especially for A. torulosa. Our results can inform Glossy black-cockatoo conservation by guiding fire management practices associated with their food trees.