Mentally you need 2 or 3 trees ahead of where you actually are, swallow tail boards make a massive difference in your ability to dodge trees at high speed. Lastly know when to bail as seen in the 2nd vid below!
tree run vids.
Snowboarding Rusutsu Japan 28/1/2012 - YouTube
Snowboarding Rusutsu Japan 28/1/2012 - YouTube