You need a mix. The owls and hawks need open flight paths. The groundcovers need light and can't survive a heavy needle drop. A few thickets in open areas serve as breeding places for critters, and then there are meadows that have the largest variety of creatures and plants while providing a place to hide out during a fire.
Complexity is where it's at.
Everybody loves a tree-church for the spriritual beauty. The more practical advantages are not as apparent.