A quick follow-up to my previous post bemoaning the lack of trees at the Magic Kingdom's central hub. Yesterday's MiceChat photo update depicts the very progression I'm talking about. (Search for the words "Walt Disney World" about 3/4ths down the page and you'll find it.) Note that even in the 1997 photo, it appears the larger trees are still there.
UPDATE: Found out that a discussion of this topic has been going on over at the Disney World Trivia forums; check it out here, along with photos. Thanks, Brian!