Who built the Disney World trees in Animal Kingdom and Swiss Family Robinson?

Both trees were designed & built exclusively by Disney Imagineers who are under contract to not give out any information about their projects.

You can find information about the heights & names of the trees, as well as other trivia about them, in the books "The Imagineering Field Guide to the Magic Kingdom" or "The Imagineering Field Guide to Animal Kingdom." The books don't give any information on the products used to make the trees however. My guess is that they don't want their competitors to be able to duplicate these kinds of things, so they don't make the information public.

Most likely the Imagineers had a contractor do it, or Buena Vista construction.

I think Rainforest Cafe has the same sort of sculptural elements.

Any theatrical sculptor should be able to do it out of foam and then covered in concrete or stucco.

odds are that disney has contracted in house for the building of those sets, that's how big companies work. 'in-house' means they hired archetects, and builders to work under the disney name this way disney owns the entire project and doesn't have to credit or pay royalties to a separate company. also they'd own all the plans and would not have to make them public knowledge

check the credits at the end of the movie and it will list the set designers