The pilot reported that he was in a descent from 5,000 feet to 3,000 feet when the engine lost power. He tried to switch tanks, but he was mainly concentrating on maintaining sight with a nearby airport. The airplane landed 400 yards short of the runway in trees. Postaccident examination of the airplane revealed that the fuel tanks had been ruptured and empty, and that nearby foliage was turning brown and dying. Examination of the engine failed to reveal a reason why the engine could not develop power.