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Information about invasive alien species and their interactions with the environment and native ecosystems is very important to prevent widespread loss of original habitats and biodiversity. Black locust (Robinia pseudoacacia) is one of the most widespread alien plant species in Europe and has become a dominant forest tree species, which is frequently planted. We analysed how environmental factors (light, temperature and humidity), species composition and level of invasion changed in black locust stands compared with those in different neighbouring native forest types (floodplain, oak and mixed oak-hornbeam forests). The aims of this study were to determine (i) how the microclimatic conditions of the native forests changed after replacing the native trees with black locust, (ii) how black locust changed species composition and level of invasion of the understory and (iii) whether black locust equally influenced the three types of native forests. The results showed that compared with those of the other forest types, the conditions of black locust stands were always warmer and drier with more light from the sparse canopy of trees. In the black locust forests, we recorded more non-forest and ruderal species with significantly higher percentage number and cover of alien species in the understory vegetation than in the native forest stands. Different native forest types and their black locust twins were mutually influenced in a different way. The mixed oak-hornbeam forest was the type most influenced by replacement with black locust, whereas floodplain forest changed the least. Black locust plantations replacing native forests cause decreasing native species biodiversity, because of the occurrence of alien, ruderal and non-forest species. The dry and warm character of black locust stands contributed to an acceleration of microclimate change. This information can be useful for forest managers and planners participating in the replacement of native forest stands by alien tree species, which has ecological and economic impacts with consequences for nature and society.