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.

Many invasive alien species (IAS) produce secondary metabolites that affect how other plants function (allelopathic compounds) and can drive other species invasion, as proposed by the invasional meltdown hypothesis. Acacia melanoxylon and Eucalyptus globulus are two of such species. In this study, we analyzed the germination response of seven IAS (Acacia dealbata, Acacia mearnsii, Acacia melanoxylon, Acacia longifolia, Eucalyptus globulus, Paraserianthes lophantha, Phytolacca americana) and a native biotest species (Lactuca sativa) to the application of two different aqueous extracts at two different concentrations of donor species A. melanoxylon and E. globulus. Extract compounds were identified by UHPLC-ESI-QTOF-MS. Eucalyptus aqueous extracts significantly reduced germination in three species (A. dealbata, E. globulus, P. americana). The germination of all the species tested was reduced with acacia aqueous extracts. Our results support the postulates of the Biochemical Recognition Hypothesis in that seeds gauge establishment potential based on phytochemical release of other plants. Furthermore, A. melanoxylon and E. globulus lowered their own germination, suggesting that these species exhibit intraspecific biochemical recognition. We also found support for the Novel Weapons Hypothesis in the case of L. sativa as a native species. Our research shows that phytochemicals are a component of plant-plant interactions, including the invasion process.

The effect of the main fire factors (smoke, ash, charcoal and heat) can influence the germination of species through their seeds. Hence, a methodology has been devised in order to have a common protocol for those who work in this area and serve as a valuable tool to compare different species that can be beneficial or detrimental to the conditions of a forest fire. Moreover, the methodology was completed with a check of the viability of the seeds before starting the germination process and another viability test with the non-germinated seeds (dormant or dead) after carrying out the germination test. In this way, the study of the main factors of fire, in combination with the study of the viability of the seeds, can be very useful to know the reproductive behaviour of herbaceous, shrub and tree species in a forest fire scenario. In addition, from the data obtained during the germination process of the seeds, a series of explained parameters can be obtained to better interpret the data acquired from the laboratory experiment and subsequent comparison. For all these reasons, the study of the germination of species in laboratory conditions can help us understand how they behave in the field.

Slash and burn treatments are often recommended and employed for controlling the invasive tree Acacia dealbata Link. In this study, we aimed to evaluate the effectiveness of this approach. We established eight experimental blocks with burn, slash and slash-and-burn treatments distributed across central Portugal. The density and height of new seedlings and resprouts of the invasive alien plant were monitored for three years. Our results showed that slash treatments stimulated resprouting, while burn treatments promoted seed germination. Resprouts and seedlings were significantly taller in the slash treatments compared to the burn treatments. When combined treatments were applied, different combinations of slash-and-burn reduced the number of resprouts and seedlings; however, the minimum stem density remained at 6.5 stems m⁻², compared to 0 in the control plots. These results demonstrate that, under the conditions of this study, slash-and-burn treatments without follow-up interventions are not effective for controlling A. dealbata populations, despite their role in reducing the soil seed bank.