Summary1. This account presents information on all aspects of the biology of Robinia pseudoacacia L. that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history and conservation. 2. Robinia pseudoacacia, false acacia or black locust, is a deciduous, broad-leaved tree native to North America. The medium-sized, fast-growing tree is armed with spines, and extensively suckering. It has become naturalized in grassland, semi-natural woodlands and urban habitats. The tree is common in the south of the British Isles and in many other regions of Europe. 3. Robinia pseudoacacia is a light-demanding pioneer species, which occurs primarily in disturbed sites on fertile to poor soils. The tree does not tolerate wet or compacted soils. In contrast to its native range, where it rapidly colonizes forest gaps and is replaced after 15-30 years by more competitive tree species, populations in the secondary range can persist for a longer time, probably due to release from natural enemies. 4. Robinia pseudoacacia reproduces sexually, and asexually by underground runners. Disturbance favours clonal growth and leads to an increase in the number of ramets. Mechanical stem damage and fires also lead to increased clonal recruitment. 5. The tree benefits from di-nitrogen fixation associated with symbiotic rhizobia in root nodules. Estimated symbiotic nitrogen fixation rates range widely from 23 to 300 kg ha À1 year À1 . The nitrogen becomes available to other plants mainly by the rapid decay of nitrogen-rich leaves. 6. Robinia pseudoacacia is host to a wide range of fungi both in the native and introduced ranges. Megaherbivores are of minor significance in Europe but browsing by ungulates occurs in the native range. Among insects, the North American black locust gall midge (Obolodiplosis robiniae) is specific to Robinia and is spreading rapidly throughout Europe. 7. In parts of Europe, Robinia pseudoacacia is considered an invasive non-indigenous plant and the tree is controlled. Negative impacts include shading and changes of soil conditions as a result of nitrogen fixation.Key-words: climatic limitation, ecophysiology, geographical and altitudinal distribution, germination, invasive, mycorrhiza, nitrogen fixation, parasites and diseases, reproductive biology, soilsFalse acacia, black locust. Fabaceae, tribe Robinieae. Robinia pseudoacacia L. is a deciduous, strongly suckering, broadleaved tree, up to 20 m high but, occasionally taller. Bark *Nomenclature of vascular plants follows Stace (2010) and, for nonBritish species, Flora Europaea.

Aim Urbanization as a major global trend profoundly changes biodiversity patterns, and homogenization of urban biotas due to expanding exotic species and declining native species is of increasing concern. Previous studies on this topic have mostly taken place at large scales that include high habitat heterogeneity. Here, we aimed at disentangling the effects of urbanization and plant invasion on species composition through the analysis of similarity patterns of urban plant assemblages at the community scale where species interact. \ud Location Berlin, Germany\ud Methods We analyzed how different levels of urbanization, specific components of the urban matrix and the dominance of a native (Betula pendula) versus an exotic tree species (Robinia pseudoacacia) affect alpha and beta diversity of urban woodland understory vegetation in 68 100-m² plots.\ud Results Exotic dominance reduced alpha diversity but not beta diversity of the total species pool. Comparing beta diversity among different species groups revealed significant but divergent effects of exotic dominance, habitat connectivity and levels of urbanization in native and nonnative species assemblages. In particular, urbanity proved to homogenize the native species pool, whereas the beta diversity of the nonnative species pool showed a more pronounced response to exotic dominance.\ud Main conclusions Our data provide evidence that both the urban context and the dominance of exotic species can modify homogenization processes at the community level. These novel insights into the mechanisms of biotic homogenization of urban floras may contribute to mitigating the effects of urbanization on biodiversity

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Regeneration is known to be limited at many temperate tree lines, but very little data is available on the impacts of altitude and anthropogenic disturbance on regeneration patterns along tropical tree lines. The study focused on the reproductive traits of two Polylepis species in the Páramo de Papallacta in Ecuador along an altitudinal gradient, and involved different intensities of cattle trampling within subsequent altitudinal ranges. We analyzed flowering, fruit set, seed viability, germination, and seedling establishment as well as stand structure of Polylepis incana and P. pauta. The numbers of P. incana inflorescences and seedlings per m 2 showed a marginally significant decrease with increasing altitude. Mean tree height was significantly lower at higher altitudes, while stem number increased. The number of P. pauta inflorescences also decreased significantly upslope. In both forest types, trampling was found to have a positive impact on seedling abundance, presumably due to the removal of the litter layer. Thus, there was no evidence of negative effects of moderate cattle grazing on both tree line species. However, sapling establishment was minimal inside the forest stands at all altitudes and grazing levels, and we consequently observed a low proportion of narrow stems within all investigated forests. Our results show that, along with vegetative growth limitations of adult trees, important regeneration traits such as seedling and inflorescence numbers are also influenced by altitude, which might contribute to the formation of the upper tree line. Nevertheless, recruitment in the forest interior was low overall indicating that further factors, such as light conditions, affect regeneration of the studied species.