I do agree that the similarities between Ferngully & Avatar can be coincidential; absolutely. As for doubting that Cameron has seen Ferngully, I don't think that's impossible at all. Directors watch movies as well as make them. In fact, I think they watch more movies than the average movie fan does. They get their ideas from numerous sources (books, foreign movies, cartoons, documentaries, word of mouth, dreams, songs, real life experiences, etc). Cameron is a huge sci-fi fan & what better source to tell a sci-fi story than through drawings in either a comic book or a cartoon? It is very possible that he saw Ferngully. Also, he's in his mid 50's. When Ferngully came out (1992) he could have easily seen it. I don't mean to make claims of a rip-off here, but there is no doubt (at least to me) that he was inspired by Dances With Wolves. And so was Edward Zwick for The Last Samurai. Again, it does not matter though because many directors/writers get their ideas from other movies. I loved both Cliffhanger & the first Under Siege which were clearly made because of Die Hard.