I can't speak to how it's done in your municipality, but I can tell you how it works in mine. Tree planting ends up being cheaper than maintenance costs. While there is an overall budget for the urban forestry department, often tree plantings have matching dollars for every dollar spent. There are grants out there that will match dollars as well as private city beautification organizations that will also match. So in many instances, one city dollar spent on plantings turns into three. So it makes fiscal sense to focus on plantings. Also, we have something called a tree bank. When a business builds, it's required that that business plant a certain number of trees (both overstory and understory) on the right of way. That isn't always possible. For instance, the whole place is already concrete. They instead put money for the trees into the tree bank, which has to be used to plant trees by the city. So often it ends up with maintenance money spent on trees which pose a danger rather than ensuring trees survive it have good form.