Do indoor cats need a cat tree?

Yes, or some equivalent vertical space. Cats live in three dimensions and an indoor cat with only floor-level access is using a fraction of her territory. The form doesn’t have to be a cat tree specifically — wall shelves, the tops of bookcases, cleared windowsills, perches above doors all work. Cornell’s enrichment guidance flags vertical space as one of the most important elements of an indoor cat environment.[1] The benefits compound: better stress regulation, fewer multi-cat tensions, more visible engagement with the home. This is one of the highest-leverage and lowest-cost changes you can make.