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Homogenization and differentiation of urban tree assemblages globally

Nature Cities volume 3, pages 273–282 (2026)Cite this article

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Abstract

Urbanization is affecting biodiversity globally. Biotic homogenization is often cited as a key consequence. However, our understanding of this phenomenon may be biased by flaws in the methods used to document it. Here we estimate compositional dissimilarity among 39 urban tree assemblages worldwide while controlling for differences among regional species pools. Our results demonstrated the absence of a distinct global pattern in urban tree homogenization or differentiation. Homogenization mainly occurred among urban tree assemblages across broad geographic distances, whereas differentiation occurred at short distances. Nonnative species were a major contributing factor to these patterns. Sharing different nonnative species contributed to differentiation at short distances, whereas sharing the same nonnative species contributed to homogenization at broad distances. Our findings reveal a scale-dependent effect of urbanization on urban tree assemblages driven by nonnative species, emphasizing the global influence of urbanization on spatial patterns of biodiversity.

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Fig. 1: Locations of the 65 cities and 39 ecoregions selected for analysis.
Fig. 2: Relationship between the difference in βsim (∆βsim) and geographic distances.
Fig. 3: Geographic distribution of urban–ecoregion pairs with the most pronounced contrasts in ∆βsim.
Fig. 4: Possible pathways for introduced native and nonnative tree species that could influence the ∆βsim of urban–ecoregion pairs.
Fig. 5: Flowchart of occurrence data collection and cleansing.
Fig. 6: A conceptual framework for detecting biotic homogenization among urban areas.

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Data availability

The data that support the findings of this study are available via figshare at https://doi.org/10.6084/m9.figshare.30962240 (ref. 61).

Code availability

All code used in the analysis for this study is publicly available via figshare at https://doi.org/10.6084/m9.figshare.30962240 (ref. 61).

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Acknowledgements

We thank all the authors who contributed to our systematic literature review for sharing their data. We also thank the institutions that curate the biodiversity databases used in this study. The generous contributions made by these individuals and organizations made this study possible. This study was supported by the National Natural Science Foundation of China (grant no. 32171542 to J.Y.).

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Author notes

  1. These authors contributed equally: Xudong Yang, Jing Jin.

Authors and Affiliations

  1. Department of Earth System Science, Institute for Global Change Studies, Ministry of Education Ecological Field Station for East Asian Migratory Birds, Tsinghua University, Beijing, China

    Xudong Yang, Xinyi Liu & Jun Yang

  2. Institute of Agricultural Information, Jiangsu Academy of Agricultural Sciences, Nanjing, China

    Jing Jin

  3. Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA

    Frank A. La Sorte

  4. Center for Biodiversity and Global Change, Yale University, New Haven, CT, USA

    Frank A. La Sorte

  5. School of Tourism Ecology and Environment, Guilin Tourism University, Guilin, China

    Pengbo Yan

  6. Department of Ecology, Evolution and Natural Resources, Rutgers – The State University of New Jersey, New Brunswick, NJ, USA

    Myla F. J. Aronson

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  1. Xudong Yang
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Contributions

J.Y., X.Y. and J.J. designed the research. P.Y., X.Y. and J.J. collected data. J.J., X.Y. and J.Y. conducted the data analysis. X.Y. produced the figures. All authors contributed to writing.

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Correspondence to Jun Yang.

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Nature Cities thanks Benno Augustinus, Jian Zhang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Yang, X., Jin, J., Liu, X. et al. Homogenization and differentiation of urban tree assemblages globally. Nat Cities 3, 273–282 (2026). https://doi.org/10.1038/s44284-026-00393-4

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