# Urbanisation effects on floodplain biodiversity: what can we learn from globally aggregated field data?

Josselin Burriat, Sylvain Dolédec, Bernard Kaufmann, Barbara Belletti

► To cite this version:

Josselin Burriat, Sylvain Dolédec, Bernard Kaufmann, Barbara Belletti. Urbanisation effects on floodplain biodiversity: what can we learn from globally aggregated field data?. Conférence internationale I.S.Rivers 2025, Jun 2025, Lyon, France. hal-05178835

HAL Id: hal-05178835

https://hal.science/hal-05178835v1

Submitted on 23 Jul 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Effets de l'urbanisation sur la biodiversité des plaines alluviales : en quoi les bases de données mondiales peuvent-elles nous renseigner ?

## Urbanisation effects on floodplain biodiversity: what can we learn from globally aggregated field data?

Josselin Burriat<fnref n="1" />, Sylvain Dolédec<fnref n="1" />, Bernard Kaufmann<fnref n="1" />, Barbara Belletti<fnref n="2" />

## RÉSUMÉ

Les plaines d'inondation font partie des écosystèmes les plus menacés au monde, en raison de leur attractivité pour les sociétés humaines et des nombreux services écosystémiques qu'elles soutiennent. Malgré leur faible étendue, elles fournissent des habitats favorables à une grande diversité d'espèces, dont beaucoup sont rares ou menacées. La forte urbanisation des plaines alluviales s'accompagne de l'altération de la dynamique de débordement naturel des cours d'eau et de la construction d'obstacles à l'écoulement, de l'altération de la qualité de l'eau, etc. induisant une raréfaction et une simplification des habitats avec des conséquences délétère sur le maintien des communautés animales et végétales aquatiques et terrestres. Dans cette étude, nous visons à quantifier l'impact de l'urbanisation des plaines d'inondation sur la richesse spécifique de douze groupes d'espèces (8 d'invertébrés, 4 de vertébrés), en nous concentrant sur 1062 agglomérations urbaines de plus de 300 000 habitants, réparties dans le monde entier. Nous utilisons des données biologiques en libre accès, bancarisées à l'échelle mondiale, pour comparer la richesse spécifique des communautés urbaines à celle au bassin versant (en limitant à 300 km en amont et en aval des villes) qui leur est associé, en utilisant des techniques de raréfaction et d'extrapolation. Les résultats montrent une dégradation significative, à l'échelle mondiale, de la richesse spécifique des communautés urbaines pour huit de ces groupes.

## ABSTRACT

Floodplains are among the most threatened ecosystems in the world, due to their attractiveness by human societies and the many ecosystem services they support. Despite their small extent, they provide favorable habitats for a great diversity of species, many of which are rare or threatened. The strong urbanisation of alluvial plains is accompanied by the alteration of the dynamics of natural overflow of watercourses and the construction of obstacles to flow, the alteration of water quality, etc. inducing a scarcity and simplification of habitats with deleterious consequences on the maintenance of aquatic and terrestrial animal and plant communities. In this study, we aim to quantify the impact of floodplain urbanisation on the species richness (R) of twelve groups of species (8 invertebrates and 4 vertebrates), focusing on 1062 urban agglomerations with more than 300,000 inhabitants, distributed around the world. We use open access biological data, aggregated at a global scale, to compare the species richness of urban communities (Rup) to that of its associated catchment (Rcp - 300 km up and downstream cities) using rarefaction and extrapolation techniques. The results show a significant degradation in the species richness of urban communities for eight of these groups on a global scale.

## MOTS CLÉS

Erosion de la biodiversité, large échelle, plaines alluviales, richesse spécifique, urbanisation

Biodiversity loss, global scale, floodplains, species richness, urbanisation

<footnote n="1">¹ Université de Lyon, UMR 5023 Ecologie des Hydrosystèmes Naturels et Anthropisés, ENTPE, CNRS ; Université Lyon 1, Villeurbanne, F-69622 Lyon, France</footnote>

<footnote n="2">² CNRS, UMR 5600 Environnement Ville Société, Université Jean Monnet Saint-Etienne ; Campus Trefilerie, 6, rue Basse des Rives, 42023 Saint-Étienne cedex 02</footnote>
# 1 INTRODUCTION

By 2050, 68% of the world's 11 billion people will live in cities (United Nations, 2019). Along with climate change, urbanisation represents one of the major threats to biodiversity worldwide. Urban systems have generally developed close to rivers and their floodplains. These specific landscapes, which cover less than 3% of the Earth's surface, represent 'attractors' and 'fixers' of global urbanisation because of the many ecosystem services they provide (Schindler et al., 2014). Though, floodplains are the most vulnerable ecosystems to human activity (MEA, 2005). Main alterations to floodplain biodiversity result from (1) the degradation of water quality and habitat availability, (2) the alteration of the longitudinal connectivity, (3) the limitation of flood expansions and the resulting alteration of the nutrient cycle (Waite, 2019, Foubert et al., 2020). Many regional case studies have shown that an increase in urban pressures affects every phylum and is associated with a significant decrease in the species richness of macroinvertebrates (Cuffney et al., 2010), fishes (Morgan et al., 2005), birds (Fuller et al., 2008; Santos et al., 2024) or plants (Cao et al., 2020). In contrast, studies that analyse this phenomenon at a global scale are scarce, generally lack methodological uniformity (Gál et al., 2019) or are derived from extrapolations based on abiotic variables, with few validations (Kuiper et al., 2014).

The unprecedented increase in the quantity of globally distributed biological data over the last decade (Heberling et al., 2021) and the development of database initiatives (GBIF, PREDICTS, GenBank, etc.) offer perspectives to assess the impact of urbanisation on species richness, yet unexplored at a global scale. The initiative that stands out for the quantity of biological data available in open access is the Global Biodiversity Information Facility (GBIF), which includes more than 3 billion observations, contributed by more than 2,000 publishing institutions (available at https://www.gbif.org [21 November 2024]). Even if the availability of such a database offers major perspectives, there are however several limits to their use, related to taxonomic biases, heterogeneity in protocols (Isaac et al., 2015), societal preferences (Troudet et al., 2017) and countries' awareness or resources (Boakes et al., 2015).

In this study, we therefore seek to determine (1) to what extent such database can inform on the effects of urbanisation on floodplains' species richness worldwide, (2) for which phylum such trends can be identified, and (3) whether urbanisation has a greater impact on certain groups of taxa.

# 2 MATERIALS AND METHODS

## 2.1 Site selection

We considered urban agglomeration exceeding 300,000 inhabitants as urban sites (UN 2019). The city centre was spatially defined as the “High Density Cluster”, proposed in GHS-SMOD R2023A (Schiavina et al., 2023). For the purpose of our study, we retained those sites that intersected rivers larger than 30-60 m resulting in a total of 1062 study sites overlapping the GFPLAIN250m data extent (Nardi et al., 2018). For each site, clipping the GFPLAIN250m layer to the WWF HydroSHEDS Basins (Lehner & Grill, 2013) at the 6th level basin subdivision (Strahler order) and extending downstream within a 300 km buffer at level 9th basin subdivision provided the “catchment scale” (further named catchment). Further clipping the GFPLAIN250m layer to the GHS-SMOD R2023A “High Density Cluster” provided the “urban scale” (further named urban).

## 2.2 Biological data

Biological data were extracted from the GBIF (GBIF.org, 2024) on May 30th, 2024, considering the occurrences of animals and plants between January 1st, 2020, and December 31st, 2023. Those occurrences with a spatial coordinate uncertainty > 250 m were excluded to match the resolution of the GFPLAIN250m raster layer. From this extraction and the scales defined above, we were able to further establish an expected pool of species (catchment) and a pool of species filtered by urbanisation (urban) at each site. In the following, we present those results concerning Animalia species only.

## 2.3 Data analysis

To ensure the comparison of species richness between the urban and the catchment pools for a given group of species, we computed the revised sample coverage index for both scales computed from the entropart R package (Marcon & Hérault, 2015). The selected sites were the ones where both urban and catchment pools reached a minimum sample coverage of 0.9, a threshold commonly applied (Chao et al., 2014). The same procedure was applied for each group of species.

To make the pools comparable, we further applied rarefaction and extrapolation methods (Chao et al., 2014)
using the iNEXT R package (Hsieh et al., 2024). The urban pool effort (i.e number of occurrences in the urban pool, Eup) is always lower than the catchment pool effort (i.e number of occurrences in the catchment pool, Ecp) as the previous one is nested into the latter. We further defined the target sample size (until which to rarefy and extrapolate) for a given combination of pools as two times the Eup (if Ecp > 2* Eup) or as equal Ecp (if Ecp < 2* Eup). The iNEXT method returned an extrapolated species richness (Rext_up) for each urban pool and a rarefied (Rrar_cpl) species richness for each catchment pool and each group of species. We computed the differences between Rext_up and Rrar_cpl to quantify the species richness loss at each urban site. We then computed the Rext_up to Rrar_cpl ratio allowing us to assess how close the species richness of the urban pool compared to the species richness of the catchment pool (our "reference" pool) for each site.

Average differences between Rext_up and Rrar_cpl were computed for each group of species. Student's t-Test was performed in case of normality (Shapiro-Wilk Normality Test, p > 0.05) and a Wilcoxon Rank Sum and Signed Rank Tests if not (p<0.05). We used non parametric ANOVA to test for differences in the Rext_up to Rrar_cpl ratio across the groups of species allowing us to assess the impact of urbanisation on the species groups.

## 3. PRELIMINARY RESULTS

The continent with most cities located in floodplains is Asia (n=596 out of 1062 sites), then comes Europe (n=165), North America (n=131), Africa (n=91), South America (n=73) and Oceania (n=6). The total number of floodplain occurrences retained for the study equalled 3,033,097 (Ecp), including 530,426 at the urban scale (Eup). According to the rules of their associated occurrences being located in floodplains embedded in their catchment area, the final number of retained sites included various group of species and phyla: Clitellata (n=13 sites), Trichoptera (n=18), aquatic Gastropoda (n=25), Bivalvia (n=44), Malacostraca (n=78), Lepidoptera (n=312), Fishes (n=147), Amphibia (n=156), aquatic macroinvertebrates (n=175), Odonata (n=216), Mammalia (n=100), and Aves (n=441). The threshold of 0.9 for coverage index in the catchment and urban pools was reached for 3 sites for Trichoptera, 6 for Clitellata, 10 for aquatic Gastropoda, 11 for Bivalvia, 20 for Malacostraca, 28 for Lepidoptera, 30 for Fishes, 49 for Odonata, 52 for aquatic macroinvertebrates, 73 for Amphibia, 100 for Mammalia, and 136 for Aves.

The group of species were differently impacted by floodplain urbanisation. Birds were the most impacted group with an average estimated Rext_up to Rrar_cpl ratio of 0.65 (p = 3.24e-23), and Gastropoda were the least impacted with a ratio equal to 0.72 (p = 0.01). The ratios of four groups (Clitellata, Bivalvia, Trichoptera, Malacostraca) showed no evidence for being impacted by urbanisation (Fig. 1).

<figure><img src="image_2.png" /><figcaption>Fig. 1 Extrapolated urban to rarefied catchment species richness ratio in each group of species retained in the study. Within each larger grouping (Invertebrates, Vertebrates, Aquatic) ratios are ordered by ascending median. The taxonomy of species strictly aquatic was extracted from the freshwaterecology.info database (Schmidt-Kloiber et al., 2019).</figcaption></figure>

## 4 DISCUSSION

The findings of our study clearly show that (1) data aggregated through international initiatives shows major taxonomic and spatial biases. For example, urban/catchment-aggregated occurrences could be compared for
only 3 sites for Trichoptera and for 136 sites for birds, and almost all of them located in the northern countries. Furthermore, a dissymmetry occurred in the amount of data collected within and outside urban centers, which makes the comparison of pools challenging. One explanation for these heterogeneities lies in the societal preferences, differences in the completion of monitoring network, difficulties of setting up the study device for observation/identification (Amano et al., 2016; Knapp et al., 2021), as well as countries' wealth, security or education level (Amano & Sutherland, 2013) and on a still low attention to urban biodiversity (Isaac et al., 2015; Martin et al., 2012); (2) our results show a significant decrease in species richness for 8 groups, regardless of whether they are vertebrates or invertebrates, aquatic or terrestrial. The replacement of vegetation by impervious surfaces, which result in a loss of habitats, represents a common threat for all animal groups. (3) Among the 12 groups studied, birds experience the most significant alteration in species richness. This can be explained by their needs for larger home ranges and for some species by the decline of the density of native trees in urban areas (Reis et al., 2012). In addition, we found that the average loss of species facing urbanisation was comparable for birds and Lepidoptera. Our findings are in accordance with previous studies that have highlighted that trends in the species richness of Lepidoptera followed those of birds (Blair 1999). In contrast, gastropods' richness showed a weak response to urbanisation, probably because their dominance in urban streams is most likely a result of the increased availability of algae and macrophytes linked to the increased input of nutrients (Wiederkehr et al., 2020).

Our study sheds important light on the erosion of biodiversity associated with urbanisation and is encouraging for further analyses, which will aim at (1) assessing the effects of competition by invasive species within urban environments; (2) comparing the species ecological preferences or specialisation/adaptation to urbanisation; (3) inferring the loss or degradation of ecosystem services through functional traits; and (4) assessing links between the responses of selected taxa and urbanisation pressures (e.g. urban sprawl, demographic growth, pollutants).

# 5 ACKNOWLEDGEMENTS

This work was cofunded by the Labex IMU (ANR-10-LABEX-0088) and the EUR H2O'Lyon (ANR-17-EURE-0018) of Université de Lyon within the programme 'Investissements d'Avenir' operated by the French National Research Agency (ANR). This research is supported by the GloUrb project (ANR-22-CE03-0005).
BIBLIOGRAPHIE

Amano, T., & Sutherland, W. J. (2013). Four barriers to the global understanding of biodiversity conservation: wealth, language, geographical location and security. *Proceedings of the Royal Society B: Biological Sciences*, 280(1756), 20122649.

Amano, T., Lamming, J. D., & Sutherland, W. J. (2016). Spatial gaps in global biodiversity information and the role of citizen science. *Bioscience*, 66(5), 393-400.

Blair, R. B. (1999). Birds and butterflies along an urban gradient: surrogate taxa for assessing biodiversity?. *Ecological applications*, *9*(1), 164-170.

Boakes, E. H., McGowan, P. J., Fuller, R. A., Chang-qing, D., Clark, N. E., O'Connor, K., & Mace, G. M. (2010). Distorted views of biodiversity: spatial and temporal bias in species occurrence data. *PLoS biology*, *8*(6), e1000385.

Cao, Y., & Natuhara, Y. (2020). Effect of anthropogenic disturbance on floristic homogenization in the floodplain landscape: insights from the taxonomic and functional perspectives. *Forests*, *11*(10), 1036.

Chao, A., Gotelli, N.J., Hsieh, T.C., Sander, E.L., Ma, K.H., Colwell, R.K. & Ellison, A.M. (2014). Rarefaction and extrapolation with Hill numbers: a framework for sampling and estimation in species diversity studies. *Ecological Monographs*, *84*: 45-67.

Cuffney, T. F., Brightbill, R. A., May, J. T., & Waite, I. R. (2010). Responses of benthic macroinvertebrates to environmental changes associated with urbanization in nine metropolitan areas. *Ecological applications*, *20*(5), 1384-1401.

Foubert, A., Lecomte, F., Brodeur, P., Le Pichon, C., & Mingelbier, M. (2020). How intensive agricultural practices and flow regulation are threatening fish spawning habitats and their connectivity in the St. Lawrence River floodplain, Canada. *Landscape Ecology*, *35*, 1229-1247.

Fuller, R. A., Warren, P. H., Armsworth, P. R., Barbosa, O., & Gaston, K. J. (2008). Garden bird feeding predicts the structure of urban avian assemblages. *Diversity and distributions*, *14*(1), 131-137.

Gál, B., Szivák, I., Heino, J., & Schmera, D. (2019). The effect of urbanization on freshwater macroinvertebrates–knowledge gaps and future research directions. *Ecological indicators*, *104*, 357-364.

Heberling, J. M., Miller, J. T., Noesgaard, D., Weingart, S. B., & Schigel, D. (2021). Data integration enables global biodiversity synthesis. *Proceedings of the National Academy of Sciences*, *118*(6), e2018093118.

Hsieh, T. C., Ma, K., & Chao, A. (2016). iNEXT: an R package for rarefaction and extrapolation of species diversity (Hill numbers). *Methods in ecology and evolution*, *7*(12), 1451-1456.

Isaac, N. J., & Pocock, M. J. (2015). Bias and information in biological records. *Biological Journal of the Linnean Society*, *115*(3), 522-531.

Marcon, E., & Hérault, B. (2015). entropart: An R package to measure and partition diversity. *Journal of Statistical Software*, *67*, 1-26.

Martin, L. J., Blossey, B., & Ellis, E. (2012). Mapping where ecologists work: biases in the global distribution of terrestrial ecological observations. *Frontiers in Ecology and the Environment*, *10*(4), 195-201.

MEA (2005) Ecosystems and human well-being: current state and trends. World Resources Institute, Washington.

Morgan, R. P., & Cushman, S. F. (2005). urbanization effects on stream fish assemblages in Maryland, USA. *Journal of the North American Benthological Society*, *24*(3), 643-655.

Nardi, F., Annis, A., Di Baldassarre, G., Vivoni, E. R., & Grimaldi, S. (2019). GFPLAIN250m, a global high-resolution dataset of Earth's floodplains. *Scientific data*, *6*(1), 1-6.

Reis, E., López-Iborra, G. M., & Pinheiro, R. T. (2012). Changes in bird species richness through different levels of urbanization: Implications for biodiversity conservation and garden design in Central Brazil. *Landscape and urban planning*, *107*(1), 31-42.

Santos, E. G., Wiederhecker, H. C., Pompermaier, V. T., Gainsbury, A. M., Schirmer, S. C., Morais, C. V. F., ... & Marini, M. Â. (2024). Urbanization reduces diversity, simplifies community and filters bird species based on their functional traits in a tropical city. *Science of The Total Environment*, *173379*.

Schindler, S., Sebesvari, Z., Damm, C., Euller, K., Mauerhofer, V., Schneidergruber, A., ... & Wrbka, T. (2014). Multifunctionality of floodplain landscapes: relating management options to ecosystem services. *Landscape Ecology*, *29*, 229-244.

Schmidt-Kloiber, A., Bremerich, V., De Wevere, A., Jähnig, S., Martens, K., Strackbein, J., ... Hering, D. (2019). The Freshwater Information Platform: a global online network providing data, tools and resources for science and policy support. *Hydrobiologia*, *5*, 1-11.

Tockner, K., Pusch, M., Borchardt, D., & Lorang, M. S. (2010). Multiple stressors in coupled river–floodplain ecosystems. *Freshwater Biology*, *55*, 135-151.

Troudet, J., Grandcolas, P., Blin, A., Vignes-Lebbe, R., & Legendre, F. (2017). Taxonomic bias in biodiversity data and societal preferences. *Scientific reports*, *7*(1), 9132.

UN. (2019). World urbanization prospects 2018: Highlights.

Waite, I. R., Munn, M. D., Moran, P. W., Konrad, C. P., Nowell, L. H., Meador, M. R., ... & Carlisle, D. M. (2019). Effects of urban multi-stressors on three stream biotic assemblages. *Science of the Total Environment*, *660*, 1472-1485.

Wiederkehr, F., Wilkinson, C. L., Zeng, Y., Yeo, D. C., Ewers, R. M., & O'Gorman, E. J. (2020). Urbanisation affects ecosystem functioning more than structure in tropical streams. *Biological Conservation*, *249*, 108634.