Urban refugia sheltering biodiversity across world cities

Over the last years, world cities have emerged as multiple and complex habitats hosting numerous and varied urban refugia for biodiversity. Therefore, the published literature was systematically reviewed to investigate the increasingly acknowledged role of many urban habitats to function as refugia for species. Many plants and animals were reported to colonize a variety of urban environments: Urban forest/grassland (natural/seminatural), City park, Historical park (villa garden, botanical gardens, cemeteries, etc.), Green spaces (abandoned areas, railways, line of trees, etc.), Water body, and Built area. Refugia were found in over a hundred world cities, especially in medium- to very big-size cities. The number of papers focusing on animals (n = 66) were higher than those regarding plants and mushrooms (n = 19 and n = 1, respectively); however, the number of species recorded within refugia were the highest for plants. Plants exhibited the highest frequency (7 out of 19 papers) in Historical park, while animals in Urban forest/grassland (20 out of 66 papers). In most studies (25.9%), urban refugia were linked to Urban forest/grassland that is terrestrial natural and seminatural sites widespread within or around cities. The 22.3% of studies referred to generic Green spaces of several types interspersed within cities, both public and private. The 14.1% of refugia were found in Built area (artificial). About the 33% of studies reported the presence of species worthy of conservation (rare, endemic, endangered, or protected) for a total of 365 species. The 20% of investigated papers reported the presence of alien species for a total of 879 species. Invasive alien species recorded within refugium areas should be subjected to control measures to prevent degradation to refugia. Overall, the capability for urban areas to host a huge amount of biodiversity needs to be acknowledged by city planners so that management practices that maintain and support such diversity can be pursued. Recording and monitoring species along with their refugial habitats is fundamental to achieve this goal.