The role of fire in the germination of invasive plants in Mediterranean environments: A meta-analysis

Fire is a key trigger for the germination of serotinous plants in Mediterranean environments. Despite the availability of ample investigations into how fire contributes to plant fitness and germination patterns in pyriscent plants, there is no published content on how fire and associated heat and smoke factors influence germination of the group of plants successfully invading a particular biome. In this meta-analytic study, 29 studies were collated regarding the effects on germination of the temperature range corresponding to Mediterranean subsoil fire temperatures (50–99 °C), and a further 29 experiments were used to reveal the effects on germination of soil surface temperatures (100–120 °C) during Mediterranean fires. 24 studies were selected to investigate the effects of smoke during a shorter and longer exposure duration to reveal the boundaries of imbibition and toxicity associated with fire smoke. The chosen experiments performed heat shocks or smoke treatments on the invasive species found in the Mediterranean biome- a part of the globe that experiences periodic, extensive fire regimes. These experiments were then subsequently categorized into herbaceous or ligneous plants to study whether type of serotiny is associated with morphology life history. The results showed that generally, soil fire temperatures have a positive effect on the germination rate of invasive plants but only significantly in the case of invasive ligneous plants. Additionally, subsoil fire temperatures trigger invasive plant germination significantly, whereas soil surface fire temperatures do not. Only short exposure periods (c.a. 5 min) to smoke produced a positive effect in the germination of invasive plants. Longer exposures can be toxic and prevent germination. Herbaceous invasive plants responded positively to smoke treatments and ligneous invasive plants responded positively to heat shock. Our results highlight the importance of fire components (high temperature and smoke) in the success of many invasive plant species in Mediterranean environments.