Invasive alien plants in Polish national parks-threats to species diversity.

Due to the relevance of protected areas to the conservation of native biota, the magnitude of invasions and threats posed by alien plants are currently important issues for the preservation of these areas. The paper summarises data on invasive alien plant species presence in the most valuable protected areas in Poland, i.e. national parks (NPs). We investigated the distribution of invasive alien plant species and management attempts concerning those species. We analysed data obtained from 23 national parks originating from published and unpublished sources. Invasive plants were present in all protected areas analysed, from two to 42 species in a particular national park, and 68 in total. The most widely distributed species were: (present in 19 NPs), (17), (17), (17), and (16). The conducted analyses showed that the number of invasive species decreased with the higher altitude (asl) of the national park. The most often managed species were (being removed in seven NPs), (six), (four) and (four). In the majority of NPs, control activities are limited to small areas and singular species, thus having an incidental character. Only in five objects (Białowieża NP, Biebrza NP, Kampinos NP, Tuchola NP, Wigry NP), management has been focused on several species. We conclude that a lack of comprehensive management of invasive plant species in the majority of national parks currently limits the effectiveness of IAS (invasive alien species) eradication. Exchange of expertise among protected areas, documenting best practice examples, synthesising lessons learnt in IAS management, as well as the development of minimum standards for invasive plants surveillance and management are pivotal.