I know this is a little vague, but it's been a long time since I read the book. If I remember correctly, the guys world is a forest and it rains all of the time. It's science fiction and the main character is a young guy. I read it in English in the early 80s. By today's standards it was a short novel, probably less then 130 pages.
On further reflection, I seem to recall the author may have written about Saturn - anybody remember any stories about rainforests on Saturn?