As the Lorax movie Director Chris Renaud explains:

“We came up with the idea to have Thneedville be a bit more relatable. It’s like Vegas or Disneyland or Abu Dhabi. We see ourselves in it a bit, and it is kind of fun. There are inflatable bushes and mechanical flowers and trees, and it’s a place with no real nature. Everyone seems to be happy, and they have everything they want: from giant cars to robots and other mechanical devices. But then it becomes a question about sustainability. While all this stuff is fun and great, is it in balance with the broader planet, and how do we maintain that balance?”

It begins with the efforts of a teen boy Ted, trying to figure out what lies outside the walls that surround the city where he lives. The city is a corporate-controlled environment where everything is plastic, including the trees. The richest man makes his fortune by selling bottled purified air to the populace. There are rules that prohibit anyone going outside the walls. In spite of this, Ted ventures outside to see what exists in the wasteland. He runs across the home of the Once-ler (with the voice of Ed Helms) who, with a lot of coaxing, tells Ted the story about long ago and what happened. 

When the Once-ler was a young man he invented a thing called a "Thneed." The Thneed was made from the Truffula trees. At first no one wanted a Thneed but then it became the height of fashion. To keep up with the demand for Thneeds the Once-ler embarked on a mission to cut down every Truffula tree until there was not even a single one left. He is warned against doing this by the Lorax who represents a voice of reason and nature. The Lorax tries to explain the impending environmental disaster. But nothing stops progress until the very last Truffula tree is cut down. After that, everything stops because there is nothing more to be done and no more resources to work with. The Once-ler falls from high position of wealth and power into despair and isolation. 

Ted learns he has a chance to restore the Truffula trees and that there is a seed for a single one. He takes this seed back to the city and nurtures it to life, finally reversing the path of environmental destruction to the delight of the citizenry.

 http://www.thesmartmama.com/lessons-from-the-lorax-hope-will-change-the-world/