Beta diversity of urban floras among E uropean and non‐ E uropean cities

Abstract

Aim Cities represent an ideal study system for assessing how intensive land‐use change and biotic interchange have altered beta diversity at broad geographic extents. Here we test the hypothesis that floras in cities located in disparate regions of the globe are being homogenized by species classified as invasive (naturalized species that have spread over a large area) or as a E uropean archaeophyte (species introduced into E urope before ad 1500 from the M editerranean Basin). We also test the prediction that the global influences of European activities (colonization, agriculture, commerce) have supported this outcome. Location One hundred and ten cities world‐wide. Methods We examined the richness and composition of urban floras among E uropean ( n = 85) and non‐ E uropean cities ( n = 25) for species classified as native or non‐native, or further classified as E uropean archaeophyte or invasive. We modelled how geographic, climatic and anthropogenic factors were related to compositional similarity between E uropean and non‐ E uropean cities. Results We found that most plants in the cities we examined, particularly non‐ E uropean cities, were native and unique to each city. Non‐native species were similarly unique, but occurred in much lower proportions relative to natives. Although E uropean archaeophytes and invasive species also occurred in lower proportions, they had similar compositions among cities. E uropean archaeophytes were most prevalent in E uropean cities, but were most similar among non‐ E uropean cities. Contrasting E uropean and non‐ E uropean cities, geography and climate were most relevant for native and invasive species, whereas climate and agriculture were most relevant for E uropean archaeophytes. Main conclusions Cities in disparate regions of the globe retain regionally distinct native and non‐native plant assemblages, while invasive species, and especially E uropean archaeophytes, were associated with lower beta diversity among cities. These findings suggest that intensive land‐use change and biotic interchange, shaped through E uropean influences, have had a world‐wide effect on the beta diversity of urban plant assemblages.

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