Novel by Larry Niven
This fabulous novel is set in a fantastical world - the free-fall environment in a torus-shaped gaseous cloud surrounding a neutron star. Life has evolved in an oxygen envelope inside the 'The Smoke Ring' (the habitable part of the gas cloud) to take advantage of the unique conditions. The trees of the title are miles-long trunks, tipped with branches at both ends, which bend in the direction of prevailing winds to become shaped like integration signs - ∫.
The ecology includes water life in floating ponds (effectively huge water drops), a wide variety of flora and fauna (almost all of which is capable of flight) and most is edible, so the humans here (descendants from a colonisation ship's crew) are able to survive, living in and around the trees. It is above all a story of human survival and adaptation - Niven creates the credible from the incredible, even down to considering waste disposal and burial.
The human population consists of descendants of the crew and cargo ("corpsicles" - regenerated criminals) of a colony ship. The book tells of their struggles to survive in the strange and hostile environment, while the ship's onboard computer is trying to communicate with them, to bring them back to the fold.
The biology is strange, the creatures fantastical and yet believable, the social structure is understandably odd. In all honesty, this book is perfect Niven - certainly it ranks for me as one of his best, and certainly sets the scene for the sequel The Smoke Ring.
Although the concept of a tide world is so utterly fantastic and alien, reading the book makes seem it credible and comfortable. The story, characters and above all, the setting (with its sound scientific background), make this book a favourite with many fans of science fiction.