The effect of fire-related germination cues on the germination of a declining forest understorey species

Abstract

Fire is an important component of most Australian terrestrial ecosystems and exerts a major influence on plant recruitment in these systems. Seeds of species from Australian heath, woodland and grassland systems have a diverse response to fire-related germination cues. Australian forests are also subject to fire events. However, for species of these forests, the diversity of germination responses to fire-related germination cues is poorly known. This study reports on the germination response of seed of Prostanthera askania Conn (Lamiaceae), a species restricted to eucalypt forests and eucalypt forest–rainforest boundaries. Smoke and heat shock negatively interact in relation to the germination level of P. askania seed. Thus, in this study, smoke elevated the germination level of P. askania seed only in the absence of applied heat treatments. P. askania seed also displayed high levels of dormancy, but unlike some related species, smoke effected a partial dormancy break. These results suggest that low-intensity fire may be optimal for the germination of this species. This is supported by an observed germination response of this species to a low-intensity fire and low-intensity fire may be a common feature of species of rainforest–eucalypt forest boundaries. However, other species in these systems have germination levels maximised by cues associated with high-intensity fire. Shifts in rainforest boundaries, reported effects of weed invasion on fire intensity in rainforests and the reported decline of species as a result of increased fire intensity suggest that P. askania may have been disadvantaged by a range of habitat changes associated with fire regimes since European settlement.