The birch trees on Isle Royale stand tall, strong, and straight as pillars. Their white bark lightens the dark woods. Pieces of bark peel off and are carried by animals or wind as if to leave notes for hikers along the trail.
The birch trees Robert Frost wrote about were bowed down by wind, weather, or--maybe a boy riding them! Frost considers that perhaps a person could ride a birch tree all the way to heaven, which of course is foolish. Yet he ends with the line: One could do worse than be a swinger of birches.
In respect of copyright law, I offer this link to the full text of the poem:
What kind of fantastical conveyance would you like to transport you?