Nope, have never hit my head against a tree or other object other than snow. I tend to steer my board away from such obstacles with my edges. If your edges fail you can always bail on your board by falling against the mountainside packed with snow. Always a way to avoid a tree! Lol, some will say that's crazae, but doesn't mean it ain't true.
I have once or twice driven my noggen in the snow after totally messing up a backcountry kicker :P
The thread contributors can feel glad that they've convinced me to bring my helm for park use and they may also be sad because I'll never wear a helmet going down a fall line.
No offence like riding a motorcycle wearing a helmet is your prerogative man I'm sure your a great rider but when your riding steep terrain with deep snow, large drop and trees that are only spaced a few feet apart shit happens even to the best of us.