A Danish study indicated that children who were raised in a green environment have a 55 percent lower risk of developing mental disorders. For the designers of future space settlements this means that they need to ensure that there will be a substantial amount of public green.

For larger free space habitats such as O’Neill cylinders an interesting example is the Wonderwoods project in the Dutch city of Utrecht. This design by Italian architect Stefano Boeri Architetti combines high-rise buildings with forests, a concept he calls vertical forests.