Are germination cues for soil‐stored seed banks different in structurally different fire‐prone communities?

Abstract

AbstractMany plant species are dependent on soil‐stored seeds for their persistence in fire‐prone systems. Seed germination is often stimulated by fire‐related cues including heat and smoke, but the way these cues promote germination may differ between structurally distinct plant communities with historically different fire regimes. In this study, we examined the effects of heat, smoke and their interactions on the germination of soil‐stored seeds from shrubby woodlands and herbaceous forests in south‐east Australia. The effect of these treatments on species richness, diversity and composition, and species richness and density of germinants within life‐forms (grass, forb and shrub) were assessed. Soils from each community were subjected to low heat (40°C), low heat with smoke, smoke, high heat (80°C), high heat with smoke and untreated (control) before being placed in a glasshouse, where the germinants were identified and counted. Greater species richness was stimulated by high heat treatments and smoke in both communities, a trend driven by shrubs and forbs, rather than grasses. Greater species diversity was stimulated by high heat with smoke in both communities. Greater densities of grass germinants were stimulated by all treatments, except low heat, in both communities. For forbs and shrubs, the effect of treatment depended on community. Compared to the control, low heat with smoke (forbs) and both low heat and low heat with smoke (shrubs) increased densities in the woodland but not in the forest. There were unique species compositions, different from the control, in all treatments in the forest but not in the woodland, where composition in low heat was not different from the control. These results indicate the importance of high soil temperatures and smoke in both communities. In the absence of wildfires, recurring prescribed burns that heat the soil to low temperatures are likely to reduce plant richness, diversity, and density resulting in a change in understorey species composition and structure.