No abstract

Research Highlights: Data indicated that fire severity modulates natural regeneration of Cytisus scoparius and Salix atrocinerea communities and drives much stronger effects on the germination of the dominant species. Background and Objectives: Previous studies demonstrated that fire severity induces different behaviours in plant species. Mother plant age is an important feature that must also be considered in plans of forest restoration. The objectives were to determine, in field studies, the effect of fire severity on the natural regeneration of C. scoparius and S. atrocinerea communities, to know the role of mother plant age on the germination of seeds of C. scoparius and S. atrocinerea, and to quantify their germination response at different levels of fire severity, in laboratory settings. Material and Methods: We have analysed the role of fire severity on the natural regeneration of C. scoparius and S. atrocinerea communities considering cover and height. Forty 30 × 30 m plots were randomly located in C. scoparius and S. atrocinerea communities. Fire severity on the germination of dominant species was tested through different levels of smoke, charcoal, ash, and heat. Results: High severity reduced the vertical cover and growth in height of the two communities and favoured the increase of cover of woody species in the C. scoparius community and herbaceous species in the S. atrocinerea community. Mother plant age determined germination percentages of C. scoparius seeds. Germination of C. scoparius was increased by moderate heat, and heat and smoke; and fire severity greatly reduced germination of S. atrocinerea. Conclusions: The regeneration responses after fire were largely controlled by interactions between the fire severity and the individual species regeneration strategies. For restoration purposes, C. scoparius seeds should be treated with 80 °C and smoke for 10 min, in order to increase germination; however, Salix seeds should be used without treatment and immediately after dispersion.

& Key message Acacia longifolia and Acacia mearnsii exhibit different reproductive behavior (viability, germination, and dormancy) in relation to fire and seed maturation. The potential of invasion of A. longifolia is stronger than that of A. mearnsii. A. longifolia germinates abundantly between fires and after fires, while A. mearnsii only 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.

No abstract

<p>Forest fires are a global problem that affects almost all parts of the world. Southern Europe has been a fire prone area since prehistoric times. The northwest of the Iberian Peninsula, despite being an area abundant in rainfall, is currently a hotspot for forest fires. Forest fires produce carbon and ash as a result of the combustion of vegetation, these products can affect the germination behavior of plants.</p><p>Due to climate change, forest fires are becoming more severe, more intense and more recurrent, and this context of disturbances facilitates and accelerates the replacement of native species by invasive alien species in many forest ecosystems. For this reason, we propose to compare the role of carbon and ash in the germination of two native species versus two invasive alien species. The two selected native species were <em>Pinus pinaster</em> Aiton and <em>Salix atrocinerea</em> Brot. and the two invasive species <em>Paraserianthes lophanta</em> (Willd.) I.C. Nielsen and <em>Acacia melanoxylon </em>R. Br. For it, 5 concentrations of ash and 1 concentration of carbon from 2 different origins (carbon from the same studied species and carbon from <em>Ulex europaeus</em> L.) were applied to seeds of these species. Mainly it stands out that the control germination of the native species was higher than that of the invasive species and the germination obtained under ash or carbon treatments was always similar or lower than the control germination. The germination obtained with the carbon of the own species was similar to the control germination and significantly higher than that achieved with the carbon of <em>U. europaeus</em>. Germination timing depends on each species studied, and invasive species take longer to complete their germination than native species (30-42 days versus 80-125 days). The carbon of the own species did not modify the germination timing while the carbon of Ulex did it in the two native species.</p><p>Therefore, carbon and ash are two factors that modify the germination behavior of both the native species and the invasive species studied and can be used to manage plant regeneration after forest fire.</p><p><strong>Funding</strong>. This work was supported by the Spanish Ministry of Science, Innovation and Universities, the Castilla y León Regional Government, the Galicia Regional Government and the European Regional Development Fund (ERDF) in the framework of the FIRESEVES (AGL2017-86075-C2-2-R) and WUIFIRECYL (LE005P20) projects and the Competitive Reference BIOAPLIC (ED431C2019/07) and the Strategic Researcher Cluster BioReDeS (ED431E 2018/09).</p>