Urbanization signatures on climate and soils uncovered by crowd-sensed plants

Abstract Human populations are increasingly concentrated in cities, creating some of Earth’s most modified ecosystems. However, we lack concepts for assessing heterogenous urban environments, especially their soils, at large spatial scales. Here we uncover fine-scale urban climate and soil patterns across 326 European cities by using more than 80 million crowd-sensed plant observations as living sensors of the environment. In addition to the urban heat island, we identify similar contrasts between the built-up and green areas for moisture, soil pH, salinity and soil disturbance. These within-city environmental contrasts correspond to differences between cities that are about 1,500–3,000 km apart. Climate, especially soil, conditions are more similar between cities for built-up areas than for forests, indicating urban homogenization tendencies. Urban forests serve as a source of environmental diversity, cooling and moisture retention. The crowd sensing of urban environments is facilitated by their citizens, which can support science, policy and help guide urban planning toward livable cities.