Infrastructure and nature in cities Homo sapiens is becoming an increasingly urban species (Wigginton et al. 2016; Elmqvist et al. 2018; NSF AC-ERE 2018), a global shift that underscores the profound importance of understanding urban ecosystems. Cities, as concentrated consumers of energy and resources, are producers of various wastes, but they are also centers of innovation, efficiency, social networks, and solutions (David 1995; Grimm et al. 2008; Bettencourt et al. 2009; Pickett et al. 2013; Grimm and Schindler 2018). Cities are designed and built to be human habitats, and the result is urban infrastructure. Infrastructure is typically defined as the physical components of interrelated systems that provide commodities and services essential to enable, sustain, or enhance societal living conditions (sensu Neuman and Smith 2010). In its classical definition, infrastructure is generally restricted to the built [and otherwise human-constructed] environment; this is the way architects, engineers, and city planners and managers often think of it. In contrast, our focus here is on non-built "nature in cities" infrastructure and the broader adoption of a more inclusive term and concept for it: Urban Ecological Infrastructure (UEI). The traditional concept of infrastructure likely began to expand to include nature in cities with the designs

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