Fire and seed maturity drive the viability, dormancy, and germination of two invasive species: Acacia longifolia (Andrews) Willd. and Acacia mearnsii De Wild

Abstract

Key message: Acacia longifoliaandAcacia mearnsiiexhibit different reproductive behavior (viability, germination, and dormancy) in relation to fire and seed maturation. The potential of invasion ofA. longifoliais stronger than that ofA. mearnsii.A. longifoliagerminates abundantly between fires and after fires, whileA. mearnsiionly germinates after fire and needs higher thermal thresholds to break dormancy. Context: Fire affects environments through the modification of biological processes such as seed viability, dormancy, and germination. Seed maturation stage can modulate seed response to fire. Invasive alien species could be enhanced by forest fires. Aims: To analyze the viability, germination, and dormancy of two invasive alien species (Acacia longifolia and Acacia mearnsii) in relation to fire and seed maturation. Methods: Viability of seeds was obtained performing a tetrazolium test. Additionally, we obtained germination and dormancy in mature and fresh seeds simulating fire conditions through different levels of fire factors (smoke, ash, charcoal, and heat). Results: Control viability of seeds was 100% in the two Acacia species and maturation stages and severe heat reduced it to zero. Germination of A. longifolia varied depending on the maturation stage, being higher in fresh seeds. In A. mearnsii, germination did not change with maturation. In both species, heat stimulated germination by breaking seed dormancy. Seed maturation stage and fire factors affect the germination speed of each species differently. Conclusion: Fire reduces viability, stimulates germination, and breaks dormancy of the two species. Seed maturity exerts notable effects on A. longifolia reproductive behavior.