The loss of many old growth trees has already made a huge impact on the park. Remember how dark the entrance area of Frontierland used to be? The big tree in front of Zocalo died last year and was replaced with a smaller tree. In addition the Big tree next to the Mark Twain Landing feel and crushed a popcorn cart a couple of years ago and wasn't replaced at all. The whole area just doesn't seem as moody as it used to.
The Big Thunder Trail has lost a lot of its old trees. That was one of my favorite spots on a hot summer day, what with all the shade.
Many trees back stage have also been targeted for removal after one fell in a cast member area two years ago.
While sad, it is also the way of nature. Trees don't last forever, and the Santa Ana winds don't help much either. The problem is that they should have been planting replacement trees years ago, rather than waiting for them all to topple over in guest and cast areas.