You know? I've always been fascinated by "Biotechnical" designs. If I had my way with the genre, things would be more of the world in "Rayman" as opposed to the icky esthetics of H. R. Geiger. It should be fun, gentle and whimsical. Would palm trees or such hold up the rails? Electric Eel power sources, or perhaps each "Tree" (or Power plant,) provide current to run or at least light the trains? I must confess I've always liked the "Flintmobile" with it's split log frame and it's giant rollers because it just looked cool, even though it would be impossible too steer, and difficult to brake.

you seem to have gotten the idea. specially bred and genetically designed trees, would indeed hold up the vines that are the rail, as well as bearing blocks for the continous cables, turned by the water wheel, one on each side going in opposite directions, with a cable car type grip, for one or the other, depending on desired direction of travel.
at exactly the speed of the cable. which would probably not be super fast. but super steady and effortless. some assembly required, but all parts grown on yet more kind of trees. that would look like the casting sprues that come in plastic kits, except of course for being genetically designed trees.