Help identifying a science fiction/fantasy book

Hey all, I want to draw on the collective knowledge round here and help my SO identify a sci-fi novel he read sometime in the 1980s. Here’s a description of the concept: The story takes place in a massive canyon surrounded by a forest of giant trees. People live in the roots of the trees that protrude into the canyon. Cities are formed by linking roots from one side of the canyon to the other… this is called “bridging” and the people that do this are called “bridgers”. The farther down the canyon the people live, the fewer hours of sunlight they get.

Does this ring a bell with anyone? I’ve searched Amazon and Googled and all that with no luck. It’s this kind of thing that makes me glad I stuck with only a few authors, makes it easier to recall what I read :cool:

Is this it?

Ooh, that looks like a strong candidate. Amazon’s search feature kinda sucks, all my keywords are on that page!

If that is not the book you described someone has a helluva plagiarism case.