The world is continuing to urbanize. As a result, most of the interactions between humans and nature take place in cities. These interactions are varied and complex. But, contrary to past conception, urbanites do not decimate nature in cities and it continues to thrive. The rich urban biodiversity includes both endemic and cultured species. People oriented evaluations of the importance urban nature differ from evaluations focused on the ecological system. Most of the urban-economic literature has focused on estimates of the positive externalities of the proximity to nature, albeit in relations to very limited aspects of such effects. The quantification of eco-services has been only partly successful. Recently there is a growing realization that there exist associated negative externalities as well. For example, in many cities the penetration of large mammals, made possible by the morphology of built areas, is generating behavior patterns, such as at least partial changes in the spatial incidence of the demand for housing.
The paper surveys literature concerning various aspects of urban nature and its relationship to urban morphology. It raises several issues that have not been addressed sufficiently by urban nature scholarship. The commonly accepted view of ecosystem services is that the provisioning, regulating and cultural services stem from the biodiversity of the ecosystem. But, while the cultural services of ecosystems within cities may be high, they do not necessarily stem from the values of biodiversity. So is the relationship between provisioning/regulating services and biodiversity. And so the question remains open, whether future cities can sustain human welfare while retaining biodiversity patterns and function. Finally, we ask which type of species do we wish to conserve? What is the contribution of conservation biology to the issue and to what extent conservation biology and urban economy are compatible?