The movie depicts a future in which all plant life on Earth has been made extinct. Only a few specimens have been preserved just outside the orbit of Saturn, in enormous, greenhouse-like geodesic domes attached to a fleet of American Airlines "Space Freighters". Freeman Lowell (Bruce Dern) is one of four crewmen aboard the Valley Forge, one of the 2,000 metre-long freighters, and is the resident botanist and ecologist who preserves the forests for their eventual return to Earth, and the reforestation of the planet. Lowell spends most of his time in the forests, cultivating the plant and animal life.Read the rest if you want the spoilers but suffice it to say things take a turn for the dramatic pretty quickly. It was directed by Douglas Trumbull who is a special effects legend in the sci-fi world having handled them for 2001: A Space Odyssey, Close Encounters of the Third Kind, Star Trek: The Motion Picture and Blade Runner. That, my friends, is what we call a resume. Ebert gave the film four-stars when he reviewed it in 1971. Anybody seen it?
Here's the trailer from YT:
PS - I assumed there would be some reference to Silent Running in WALL-E but this page of easter eggs in WALL-E (via Waxy) doesn't seem to mention it - although I used the "find" function to avoid spoilers so I didn't read it closely.