Diversity Patterns of Alien Plant Species in Mountainous Areas: A Case Study from the Central Balkans

Due to global warming and intensified anthropogenic impacts, mountainous areas are increasingly being colonised by alien plant species. The diversity patterns of these species have not been sufficiently studied in the Central Balkans. The aims of this study were to determine the occurrence and richness of alien plant species in relation to habitat type and geological substrates, and to identify the factors with the greatest influence on the composition and abundance of these species on Zlatibor Mountain (Central Balkans). This area is known as an important tourist centre and a large mountainous massif in Serbia. Principal Component Analysis (PCA) and distance-based Redundancy Analysis (db-RDA) were employed to examine the influence of environmental factors on the abundance and composition of 18 alien plant taxa. Data on altitude, habitat type, bedrock type, bioclimatic variables, and indicator values (light regime, soil moisture, acidity, nitrogen and temperature) of dominant plant species within the habitats were used as explanatory variables. Erigeron annuus, Reynoutria × bohemica, Robinia pseudoacacia, and Erigeron canadensis were the most common alien taxa and had the highest abundances. Residential and tourist facilities and the peripheries of asphalt roads are the habitat types where most alien species occur, while the lowest number of species was found in natural and semi-natural herbaceous habitats. Most taxa were found on serpentine substrates, while the number of taxa was lower on siliceous and carbonate substrates. This study emphasises the predominant role of habitat type in the partitioning of ecological niches of alien plant species. Furthermore, habitat type has a much greater influence on species composition and abundance than climatic factors and bedrock type, suggesting that the diversity pattern of alien plant species is related to the type and intensity of anthropogenic influences. Our results provide a useful basis for developing effective strategies to protect native habitats from invasion by alien plants.