Germinative behaviour of Acacia dealbata Link, Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. in relation to fire and exploration of the regenerative niche of native species for the control of invaders

Abstract

Invasion of forest ecosystems by invader plants and forest fires are two of the most serious environmental problems in the world. Climate change is believed to strongly influence these processes, and the invasibility of invasive alien plants (IAPs) is likely to enhance landscape degradation. Therefore, it is urgent to study the germinative behaviour of invasive alien plants in relation to fire and detect possible barrier species of IAPs among native species. Tree species are usually the most damaging group of invasive alien plants. Acacia dealbata Link, Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. are 3 very damaging exotic invader trees in Europe and many other parts of the world. Therefore, the germination behaviour (germination percentage, viability pregermination, viability postgermination and germination rate) of these three species was experimentally studied against different products associated with fire (heat, smoke, ash and charcoal). The germination of A. dealbata and R. pseudoacacia was strongly stimulated by heat, while smoke, ash and charcoal barely changed the control values. None of these factors stimulated germination in A. altissima. Very high temperatures inhibited seed germination of the three species. The germination of R. pseudoacacia seeds was faster than that of A. dealbata and A. altissima seeds. Of the three species studied, A. dealbata and R. pseudoacacia have greater invasibility than A. altissima. A key role in invasive plant control research is to provide information to guide the decisions of forest managers involved in restoration. A possible solution is to use the biotic resistance of native vegetation to control biological invasions. For this purpose and based on extensive bibliographic revision, the regenerative niches of the three invasive species (germination, seedling growth and adult height) were compared with those of native European species to identify candidates for barrier species of IAPs between native species. Among the native species of Europe with characteristics in their regenerative niche suitable to successfully compete against these IAPs are tall shrub species such as Adenocarpus lainzii (Castrov.) Castrov., Cytisus multiflorus (L'Her.) or Cytisus striatus (Hill) Rothm. and tree species such as Corylus colurna L., Pinus sylvestris L. and Quercus ilex L. Therefore, the sowing of a good combination of shrub and tree species, selected according to their geographical distribution, could be an effective ecological measure to control the invasion of IAPs in burned areas. This information can be very valuable for implementing restoration measures in burned areas and should be verified with field experiments.