Black locust--successful invader of a wide range of soil conditions.

Black locust (Robinia pseudoacacia, BL), a species native to North America, has successfully invaded many types of habitats over the world. This study provides an overall assessment of BL soil conditions to determine the range of physical-chemical soil properties it can tolerate. 511 BL stands (for the soil types) and 33 permanent plots (for the soil chemistry) were studied in the Czech Republic. Relationships among different environmental variables (physical-chemical soil properties, vegetation characteristics and habitat conditions) were investigated and variables with the highest effect on species composition were detected. The results were compared with data in the literature for other parts of the secondary and native distributions of this species. This assessment showed that BL is able to tolerate extremely diverse soil physical-chemical conditions, from extremely acid to strongly alkaline, and from medium to highly base saturated soils with a gradient of different subsurface stoniness. Soil nitrate, N mineralization and nitrification rates also varied considerably and the concentrations of exchangeable phosphorus and ammonium were consistently low. N mineralization rate, incubated inorganic nitrogen and nitrates were positively correlated with base saturation and cation exchange capacity. The most common soil types were young soils (Cambisols, Leptosols, Arenosols, and coarsely textured Fluvisols). BL seems to be limited by water supply and soil aeration and prefers well aerated and drained soils, and tolerates desiccation but avoids compact soils and areas where the soils are frequently waterlogged. On steep slopes, BL was less vigorous, stunted and less competitive. By contrast, the tallest BL trees were found on sandy soils in a flat landscape. Number and share of nitrophytes in the herb layer were positively related to basic bedrock, soil reaction and N-NO3/N ratio. Soil reaction was determined as the most important environmental characteristic explaining the variability in BL species composition in the Czech Republic.