I joke sometimes about the maps in the first pages of fantasy stories. When I opened The Integral Trees by Larry Niven, what I found were schematics. Niven, never one to shy away from building unusual worlds, outdid himself on this one. How can you create an atmosphere dense enough to breathe without a planet? Well, one way to do it is to create a donut of gas around a neutron star. Then, to make the region warm enough to support life, get that system captured by a nice yellow star.
So now we have a world that is an enormous volume of space, filled with tufts of plant life, spheres of water, and trees. The trees are vast, potentially hundreds of kilometers long, held by tidal forces with one end pointing “in” at the neutron star, the other “out”. The ends of the trees are swept by the winds of the “smoke ring” – the region of the dust torus dense enough to support life. The wind-swept ends of the trees make them resemble integral symbols from mathematics.
There are Earthlings living on the trees and in the floating puff-balls of jungles. They came in a ship long ago, but while the ship remembers them, it’s been a few hundred years and science is steadily being lost.
One thing I really liked: Language has drifted. Kilometers are klomters, which if you ask me is a way better word. Cursing and euphemisms have changed as well to match their new surroundings. A few good curse words can really frame a society. The people in the story would never, ever, use the phrase “integral tree”, and I don’t think Niven should have, either.
The biggest danger to our tree-dwelling humans is simply falling off. Humans are the only creatures in the system unable to propel themselves through the air. Everything else can — and I mean everything. If you drift too far out and don’t have a rope or pressurized seed pod to propel you back, well, you’re out of luck.
There are some interesting people in the story. Times are lean for the Quinn tribe, and they send out their cripples and dissidents on an “expedition” up the tree trunk looking for water and food, a transparent attempt by the leadership of the tribe to reduce the number of mouths to feed. The tree’s position has been disturbed and now it’s too far in. The tree is dying, though few of the tribe accept that.
The expedition reaches the midpoint of the trunk about the time we learn how it is the trees adjust their course. This does not go well for many of the people living on it, and our expedition finds itself clinging to an enormous piece of bark, drifting through the void and dying of thirst. They survive that adventure, of course, and more hardship follows.
This isn’t grand literature; while it touches on deeper themes it is first and foremost an adventure of life and death in a world more alien than most. If you like that stuff, do give this one a try.