Effects of fire season on the reproductive success of the post-fire flowerer Doryanthes excelsa

Abstract

Fire is an integral part of many ecosystems and recent record-breaking fires in natural systems around the world are indicative of changes occurring to the fire regime. Fire seasonality is one regime element that is shifting, and can impact the reproductive success of plant species, but rarely receives the spotlight when impacts of fire regimes are studied. We examined the effect of fire season on the reproductive effort and seed resourcing of the post-fire flowering Doryanthes excelsa from eastern Australia. We used field experiments at sites of different soil moisture levels (wet vs dry) burnt in different seasons (summer, autumn, spring) to measure the reproductive output of D. excelsa, including the percentage flowering and the number of seed pods. Seed vigour including seed germination and the percentages of lipids, carbohydrates, and crude proteins of seeds produced after different seasons of burn were analysed. There was a strong effect of fire season on D. excelsa reproduction, with percentage flowering, number of seed pods, germination and lipid levels in seeds all higher after summer compared to spring or autumn burns. Burns outside of summer also delayed flowering. The results of this study highlight the importance of fire and the season in which it occurs in the reproductive success of post-fire flowering species like D. excelsa, a species representative of a functional type often dominant in some fire-prone systems. Importantly, we found that the impacts of season of burn are not merely a product of differences in fire severity. Ongoing climatic changes driving shifts in the fire regime pose an imperative to consider fire season when managing to conserve this important functional group.