The idea that everything needs to be a dense forest is a problem. What is more helpful is a variety of ecosystems available. I don't have a lot of space, but I managed to have 4 ecosystems in all of my yards with 200+ species of plants: California chaparral, Coastal forest, Xeriscape and a wildflower meadow. Cities could also build such environments and that would be more positive than just planting Miyawaki Forests everywhere.