Wait? What? Avatar 2, 3 and 4?

Apparently James Cameron has been working on putting together three sequels to Avatar, all filmed at the same time. Sigourney Weaver is set to appear in all three of them, see Aintitcool.

Who came up with the idea that there should be three sequels. One might be okay, but really the movie was a rehash of Dances with Wolves on Edgar Rice Burrough's Mars so there was so little original in the first Avatar that I can't imagine what we're going to do with the second.

And didn't they blow the tree up?