Fire as driver of the expansion of Paraserianthes lophantha (Willd.) I. C. Nielsen in SW Europe

Paraserianthes lophantha (Willd.) I. C. Nielsen is a plant species native to SW Australia that has recently invaded temperate ecosystems in Europe and other areas in the world. Since it has been found in burnt areas and its expansion could be promoted by forest fires, the germination response of seeds to fire factors (heat, smoke, ash and charcoal) was analyzed. Furthermore, stochastic post-fire invasion models were developed to check the impact of one-off and repeated forest fires. The spreading pattern after fire was modeled to provide accurate forecasts for future fires. The model was parameterized using data recorded after the 2013 forest fire in the Natura 2000 site Monte Pindo. Germination response is mainly modified by heat, which breaks seed dormancy at moderate temperature and kills seeds at high temperatures. Smoke, ash and charcoal did not have relevant influence on seed germination except large amounts of ash, which prevented seed germination. Neither charcoal origin (from native or from exotic species) had a significant effect on P. lophantha germination. The invasion model demonstrated the significant role of forest fires promoting P. lophantha spreading. Recurrent fires promote the spreading of invasive species, threatening natural plant communities. However, the expansion of the species was not exclusively linked to forest fires: anthropic systems, edges of agricultural areas and old fields were particularly affected by P. lophantha expansion. Some control methods based on the reproductive behavior and spreading pattern of P. lophantha were proposed in order to prevent new invasions and manage invaded areas.