One of the nice things CM1 does is to leave a little gap in between different types of tree tiles. If you cover a 10x10 tile area with, say, pine trees, you get a 100 tile area unbroken and completely inaccessible to vehicles.
But if you were to alternate pine and woods like this:
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You would get a checkerboard tree pattern (obviously) with a narrow grid of open ground running between all squares. In a less extreme application, you can use this to make "forest trails" that vehicles can negotiate slowly. I really like this feature as an alternative to 20 meter highways or open meadows through rural forest. Of course, there's a time and place for those too.
One other note on LOS, the last time I checked (several years ago), wire emplacements were treated like open ground for LOS purposes, no matter what terrain they were set up on. This lets your defenders extend their LOS in the forest a bit as well.