Since urban forests are a product of the cities to which they are connected they differ tremendously. The urban forest of Germany's Frankfurt and Berlin and the urban forest of the United States' Los Angeles and Washington are very different, both because of differences in the historical and symbolic significance of forests, and because of very different urban morphologies. The four cases were chosen not as a way to make a comparison between German and American cases, but to present and understand very different typologies and definitions of the urban forest in relation to their urban, rather than national, context.
Three factors determine the overall urban forest structure:
Urban morphology, natural factors, and management.
"Urban morphology provides the space for vegetation and is determined by how we build our communities. Natural factors control what will grow there and include factors such as climate, soils, and topography. Management is what species and ecosystems humans elect to include and manage for in the urban landscape." (Miller, 31)
Germany has a long history of managed urban forests that is demonstrated in the case of Frankfurt and Berlin. Even before the Middle Ages cities in Germany maintained a communal forest that was used by all for hunting, grazing, firewood, and timber. As such, man intervening in the course of nature of the forest so as to increase the amount of benefits it produced is an old and established concept. In the United States, this is a relatively new concept, and not yet accepted by all. There have been, it seems, contradictory perceptions of man's role in the nature of forests. At the same time that it was being destroyed there was the belief that man had no place in restoring it. Nature would take its course and eventually regenerate, and in an almost sacred way, man had no business intervening. This still holds true for many naturalists. An example in the Anne Spirn's Granite Garden exemplifies this where a naturalist's case to prevent the cutting of diseased trees in the city of Dayton, Ohio as was suggested by the city forester, was won in court with devastating consequences. The court ruled to "let nature take its course." Luckily, it is now becoming clear to all that this argument of non-intervention has no basis when so much of the nature in question has taken its course in relationship to human involvement.
Although the cases chosen do not reflect the characteristics of all urban forests of each country, their differences provide a contrast for understanding the multifaceted notion of what is meant by urban forest, that is both related to their urban context and cultural perception.