Invasive Species and Maintaining Biodiversity in the Natural Areas – Rural and Urban – Subject to Strong Anthropogenic Pressure

Expansion of invasive species can be clearly seen all over Poland. Foreign tree and herbaceous plant species are effectively taking over more and more habitats competing with native vegetation. This phenomenon is strongly pronounced in the areas subject to strong anthropogenic pressure. The presence of invasive plants replacing the native vegetation is a threat for biodiversity and ecological balance. The research carried out by the authors between 2011 and 2017 on selected sites (comparatively: urban and open spaces, including a 600 ha park and a 10 km long forest strip along a river) confirms the pressure exerted by invasive species irrespective of the natural conditions of a particular site or its type – in each case it is most prominent in areas where vegetation is not properly maintained or where it is not maintained at all. The research was based on the dendrological inventories and phytosociological assessments. The inventories were used for a detailed assessment of both the condition and structure of treestands, including accounting for invasive species. Phytosociological assessment can, among others, form a basis for forecasting ecological stability of individual plant communities. Uncontrolled expansion of invasive species, especially in the areas of strong anthropogenic pressure, may cause unfavourable natural succession and in consequence – destabilisation of ecological system in a given area.