The morphology of the American cities of Los Angeles and Washington is that of sprawling built areas. In these cases the urban forest can be regarded as all trees that are interspersed within the built environment. (This is not to say that the German cities of Frankfurt and Berlin do not have street trees, but they are not defined as part of the urban forest.) Among others, organizations such as the Tree People in Los Angeles and Casey Trees in Washington have been working towards instilling this definition of the urban forest in the minds of the citizens of their respective cities; that being, every tree whether on a street and publicly managed, or in a backyard and privately cared for is part of the urban forest.
The Tree People in Los Angeles and Casey Trees in Washington have had a tremendous impact on the improvement of the urban forests of these cities by planting, one tree at a time, throughout the city. Their work, has not only motivated individual citizens to partake in caring for the urban forest, it has also promoted the local governments to take responsibility and accept the need for the care of its "green infrastructure."