tInvasive alien species are a threat to protected areas, species, and habitats worldwide. At the Europeanlevel, the control of invasive alien species is a major goal of the EU Biodiversity Strategy, and a cornerstone,in this sense, is the Regulation (EU) no.1143/2014 on invasive alien species. In this study, we focus onthe Alpine and Continental biogeographical regions of Europe (defined in art. 1 of the Habitats Directive;92/43/EEC), and aim to give an overview of the main protected forest habitat types threatened by invasivealien species, and focus on five major invasive alien tree species (Acer negundo, Ailanthus altissima, Prunusserotina, Quercus rubra, and Robinia pseudoacacia). We considered the assessment reports under Article 17of the Habitats Directive for the period 2007–2012, and six documents on the interpretation of habitats, toidentify those most threatened by invasive alien species and in particular by the five invasive alien trees.We also assessed selected examples of impacts by these alien tree species on different species groupswithin Natura 2000 sites to highlight potential effects on biodiversity. Riparian forest habitats and oakdominated woodlands are among the most prone to invasion within the two biogeographical regions. A.altissima and R. pseudoacacia are the most reported invasive alien trees in these protected forest habitattypes. Furthermore, examples of the impacts of these tree species have indicated potential detrimentaleffects on forest habitats structure and functions, and on single species listed in the Habitats and BirdsDirectives. In conclusion, we emphasise the need for effective management and systematic monitoringof these five invasive alien tree species within Natura 2000 sites. Keywords: Semi-natural habitat, Exotic tree, Invasive tree, Biodiversity management, Forest type, Natura 2000 Schlagwörter: natürlicher Lebensraum, Exotischer Baum, Invasiver Baum, Biodiversitätsmanagement, Waldtyp, Natura 2000
