Black locust stands along railways as novel ecosystems in northeastern Italy: structure, composition and landscape context

Railway corridors contain vegetation that may contribute to habitat availability and landscape connectivity while also creating management constraints related to periodic maintenance and safety requirements. Tree dominated railway vegeta- tion remains poorly described, particularly where it is dominated by alien species. We investigated 42 linear tree strips dominated by black locust (Robinia pseudoacacia L.) along four electrified railway lines in northeastern Italy. We quanti- fied stand structure, species richness and plant community composition, and tested whether variation was associated with railway type, track type, adjacent land use and spatial position. The sampled stands were structurally heterogeneous but strongly dominated by black locust, which represented on average 70.5% of live stems. Mean stem density, basal area and volume standardized by canopy projection area were 1,926 stems ha−1, 22.2 m2 ha−1 and 121.3 m3 ha−1, respectively. Total species richness averaged 15.7 species per 10 m segment. Railway type and track type were associated with some descriptive structural and richness differences, but multivariate composition was more consistently related to adjacent land use and spatial position. Adjacent land use was a more consistent predictor of plant community composition than railway type or track type, both for total vegetation and for the understorey. Railway black locust stands should therefore be interpreted as alien secondary woodlands, vegetation associated with infrastructure and potential novel ecosystems shaped both by environmental filters specific to railway corridors and by the adjacent landscape matrix.