Invasive alien species mainly spread in landscapes with strong human influence, where they are able tooutcompete native species over open areas. In recent years, however, a number of exotic tree and shrubspecies are spreading over Italy in disturbed environments, as well as in natural and semi-natural areas.Ailanthus altissima (Mill.) Swingle (tree of heaven) is one example of invasive alien tree species widespreadand harmful of temperate and Mediterranean forest ecosystems worldwide. From an ecological point ofview, Ailanthus shows all the typical traits of pioneer woody species: rapid initial growth, early sexualmaturity and abundant seed production with anemocorous seed dispersal. Ailanthus has an extraordinaryability to adapt to environmental conditions of intense and frequent human disturbance, and of high abioticstress, making it a symbolic plants of highly impacted and degraded areas (urban and sub-urban sites,extractive areas, landfills, etc.), with a restricted variability of environmental conditions and a low naturevalue. This undeniable peculiarity has probably contributed to underestimate and neglect the high abilitythat Ailanthus has to spread and establish in natural forest ecosystems, where it alters the forest standdynamics, making costly and difficult its management, and it also directly threatens species and habitats ofconservation interest. Even though Ailanthus seems to be capable of invading forest ecosystems with lowdisturbance, especially those with limited light availability, it is an opportunistic species and therefore, undersub-optimal conditions, can progressively invade and establish areas in which favorable conditions arecreated. The reduction of the dominant tree cover due to gap formation, or wildfires, are ecological situationsin which Ailanthus is very competitive compared to light-demanding tree species such as maples and ashtrees. After the establishment in the understory, Ailanthus may quickly reach the dominant tree layer, thustriggering a progressive and inexorable invasive process, making it very difficult to restore pre-invasionconditions, as well as natural successional dynamics. The most distinctive feature of Ailanthus is its largeecological plasticity, which has allowed it to invade a wide range of habitats, probably higher than any otherexotic woody species.
|Number of pages||2|
|Publication status||Published - 2018|