Courtesy of IMDB.com:
Ferngully is a rain-forest, it is home to a race of fairies who have never seen humans and believe Humans don't exist and only exists in stories. That is until the arrival of Batty, a wacky bat who tells the Fairies that he has seen the Humans. Curious, when she sees smoke from Mount Warning, a fairy named Crysta travels beyond Ferngully and discovers a group of humans is destroying the rain-forest. Crysta discovers a human named Zak who is helping destroy the rain-forest and accidentally shrinks him. Once discovering the beauty of Ferngully, Zak and Crysta learn the Fairies and Ferngully itself are in mortal danger, when the humans free Hexxus, a evil oil-like creature who along time ago was turned into a tree when he tried to unleash chaos in Ferngully and has taken over "The Leveler" a logging machine as he begins his evil scheme to destroy Ferngully and only Zak, Crysta, Batty, Pips and The Beetle Boys can defeat Hexxus and save Ferngully from destruction.