In recent decades, the flora and fauna of cities have become the objects of the interdisciplinary research field of urban ecology and related policies of urban nature conservation. Although the term "urban ecology" is quite recent, it is argued in this paper that the formation of urban nature as an object of ecological knowledge has a much longer history. For example, in Germany, after World War II, the large rubble areas that existed in all bombed cities soon became important research fields for botanists studying plant migration and vegetation development in the context of the city. This paper uses the case of these botanical research activities to shed light on the historical origins of ecological thinking about nature in the city. Drawi...