I read this decades ago.
The idea that there was in space, around some star, an "air" belt, like an asteroid belt, with enough atmosphere that people could live there without special life-support. Maybe there were also rocks and "dirty ice" blocks, but I am not sure. What definitely was there are huge trees, and people mostly have settled on these trees.
Since everything was rotating, Coriolis forces dominated the dynamics, so people who kept "flying" from one tree to another had developed new reflexes very unusual to us.
I do not remember much about the story itself.
I vaguely remember a very dangerous trip to a stable Lagrange point (due to the presence of a planet, probably just a planetoid, sharing the orbit of the air and the trees), but I don't remember why the trip was attempted. Possibly to recover some stuff, since in the story vagrant stuff would tend to drift towards stable Lagrange points (I believe the author did not have a very clear understanding of stable Lagrange points but this is irrelevant).
It was either a rather short novel, perhaps a rather long novella, I am not sure.