Micropolitan and ecoregional representation of urban biodiversity in the USA: a systematic literature review

Source abstract

Abstract Urban environments vary widely in their physical and ecological characteristics, yet understanding of urban biodiversity remains limited by uneven coverage of variables known to shape urban plant and animal communities. Building on and updating a global systematic review of urban biodiversity (Rega-Brodsky et al. 2022), this study synthesized 675 peer-reviewed publications reporting diversity trends of 12 taxonomic groups in cities across the United States to identify geographic (i.e., state, city), urban intensity (i.e., metropolitan and micropolitan core-based statistical areas), ecoregional, and taxonomic trends in the literature. Each study was classified by its corresponding core-based statistical area and ecoregion to assess spatial and taxonomic representation across urban systems. Results revealed that urban biodiversity research in the United States was heavily concentrated in a few major metropolitan regions (e.g., Chicago, Phoenix), with extensive gaps across the northern Intermountain West and Great Plains. Only 5% of biodiversity studies surveyed micropolitan regions, with just 1.6% focusing exclusively on these less population-dense urban systems. Over half of all urban biodiversity studies occurred within the Eastern Temperate Forest ecoregion, while the Mediterranean California ecoregion was disproportionately represented, relative to its land area. Plants and bird communities were the most frequently studied taxa, consistent with global research trends, whereas bat and arthropod communities were comparatively underrepresented across multiple ecoregions. Collectively, these findings highlight strong spatial and taxonomic imbalances in urban biodiversity research and underscore the need to expand work on understudied taxa, micropolitan areas, and ecoregions to improve understanding of how urban intensity and environmental contexts interact to shape ecological communities across the urban continuum.