Comparison of alien Robinia pseudoacacia stands with native forest stands across different taxonomic groups

There is much knowledge about the impact of non-native Robinia pseudoacacia on native ecosystems, but mostly it is related to one group of organisms. In this article, we provide an analysis of the impact of R. pseudoacacia on the surrounding biota with a broader scope in a model area with homogeneous abiotic conditions compared and analysed by the twin plots method. Microclimatic conditions and the changes in the species composition of vegetation, terrestrial gastropods, carabid beetles, bats, and acoustic diversity were analysed. The planted Robinia stands were always brighter and warmer and had lower canopy closure than the control plots in the native floodplain forest. More nitrogen and phosphorus were recorded in the soil of the Robinia stands. The floristic composition changed the most based on the planting of Robinia trees. Compared to those in the adjacent floodplain forest, more heliophilous neophytes, archaeophytes and grasses were found. Assemblages of gastropods and carabid beetles were less affected by the planting of Robinia trees and more by the microclimatic conditions of the studied locality. The number of recorded bats and acoustic diversity were higher in native floodplain forests due to food and shelter options. All results show that the planting of Robinia trees changes the microclimatic conditions and species composition of forest stands. The warmer and less humid environment under Robinia stands is not desirable in the face of ongoing climate change. The alien (including invasive) and ruderal plant species in the understorey are supported due to the more favourable brighter conditions and nitrogen fixation in the soil. Additionally, the other groups of organisms react negatively to changes under Robinia trees in terms of microclimatic conditions, food and shelter sources. Therefore, forest managers, policy-makers and conservation workers should choose stratified management when deciding whether and where to plant R. pseudoacacia.