The Complex Botanical Impact of the Invasive Black Locust (Robinia pseudoacacia L.) Around Lake Kolon

Although Robinia pseudoacacia L. (black locust) is of major importance in forestry and an excellent honey-producing plant species, it is also an alien invasive species that can cause negative environmental impacts. The main objectives of this paper are to compare species richness, diversity, and social behavior types of stands degraded by R. pseudoacacia and nearby natural control stands, in the area of Lake Kolon, Hungary. The botanical survey was conducted in 2001 and 2002, in spring and autumn each year. Different biodiversity indices (Shannon, Simpson, Rényi and individual rarefaction profiles) were used for the analysis complemented by multivariate methods. Our results show that the natural control stands were more species-rich than the R. pseudoacacia-dominated stands. The analyses also revealed subtle seasonal and interannual dynamics. In both stand types, herb-layer diversity was slightly higher in 2022 than in 2021, with natural controls showing more pronounced interannual fluctuations. In the stands dominated by R. pseudoacacia, the canopy and shrub layers were dominated by non-native aggressive competitors (AC). At the same time, nitrophilous species were the most abundant in the herb layer, such as Bromus sterilis L., and Anthriscus cerefolium (L.) Hoffm. In the natural control stands, the canopy and shrub layers were dominated by competitors (C) (e.g., Fraxinus angustifolia Vahl. subsp. danubialis Pouzar) and generalists (G) (e.g., the native Populus spp.). In the herb layer, several species representing different social behavior types occurred at higher abundance. Overall, the natural control stands exhibited substantially higher species diversity across all vegetation layers than the stands dominated by R. pseudoacacia. Therefore, from a nature conservation perspective, the control of R. pseudoacacia is recommended in the invaded stands, especially in protected areas. Engagement of the stakeholder groups holding economic interests in the cultivation of the species seems necessary to avoid conflicts.