Abstract
AbstractAimExploring the biotic homogenization and diversity resistance hypotheses by assessing the effect of non‐native black locust canopy on understorey species turnover.LocationBerlin, the Venetian metropolitan area, and Rome.MethodsWe modelled the zeta (ζ) expression of diversity to compare the understorey species turnover between the non‐native black locust and native woodland canopies across multiple sites and through predictors of anthropogenic pressure (road and built‐up density) and interior conditions (tree basal area and mean height).ResultsIn Rome, black locust showed the lowest survivability and cover and did not produce any homogenization of the understorey. In Berlin and in the Venetian metropolitan area, black locust caused understorey homogenization, although with a lower intensity in Berlin. Under black locust canopies, distance between sites and road density was more consistently associated with species turnover, across urban areas and multiple sites. Under native canopies in Berlin, factors prominently associated with species turnover were road and built‐up density and mean tree height, while in the Venetian metropolitan area it was road density.Main conclusionsEvidence in support of the biotic homogenization in contrast to the diversity resistance hypothesis varied across urban areas. Species turnover was influenced by land use patterns more evidently under native tree canopies and where the non‐native tree had higher survivability. Similar analyses in other urban areas may confirm these relationships with other types of landscapes.
Highlights
Land use patterns determined by city growth are among the main drivers of urban plant diversity at the landscape scale
Our results provided insights into the homogenization brought by black locust, the most invasive tree non-native to Europe, on the understorey of wild woodlands of three urban areas
We deepened the understanding on how changes in the rate of species turnover, the process that drives homogenization, are influenced by anthropogenic disturbance, interior conditions, spatial scale and level of species commonness
Summary
Land use patterns determined by city growth are among the main drivers of urban plant diversity at the landscape scale. We focus on wild urban woodlands developed on vacant or abandoned urban land uses (Kowarik, 2021), and their plant communities are affected at the landscape scale by anthropogenic pressures from the surrounding built-up areas and road networks (Kowarik, 2005; Kowarik et al, 2019; Trentanovi et al, 2013) Species composition of these woodlands correlates with stand factors, such as density and height of the tree canopy, indicators of interior conditions. We aimed at identifying the drivers of understorey spatial species turnover across three urban areas that differed in black locust survivability and in land use patterns We suggest that both the biotic homogenization and the diversity resistance hypothesis could explain any of the differences we may find between the understorey of the two canopy types. We expect that the association of anthropogenic pressure and interior conditions with spatial species turnover at the landscape and at the local scale will differ across the three urban areas
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