What effect do ice-storms have on birch trees in the poem "Birches" by Robert Frost?

In the poem “Birches” by Robert Frost, the speaker is reminded of his own childhood, living “too far away from town for baseball,” amusing himself by swinging down to the ground from the tops of birch trees.  He recalls this memory fondly, and upon seeing birches with their trunks bent low, he says, “I like to think some boy’s been swinging them,” as he himself used to do.  But no boy has been there, for “Swinging doesn’t bend them down to stay/As ice storms do.”  So we know that an ice storm is the culprit for the current configuration of the birches.  Frost describes what happens to birches in an ice storm with as much nostalgia as he does his own swinging, another indication that birches – and by extension nature in general – played a large role in the speaker’s upbringing.  When there is ice on the birches after a rain, he says,

…They click upon themselves
As the breeze rises, and turn many-colored
As the stir cracks and crazes their enamel.
Soon the sun’s warmth makes them shed crystal shells
Shattering and avalanching on the snow crust

Here we get a smorgasbord of sensory imagery:  the sound of the ice clicking and cracking as the wind sways the trees, the feel of the warm sun, which we can contrast with the chill of the air suggested by the snow; the shifts in color caused by the cracking and the resplendent sparkle of thousands of shards of ice finally released to fall onto the ground below the branches.  And during this whole enchanting process, the birch trees are being pulled all the way to the ground by the load.  And so, after bearing their icy burden for hours on end, the birches do not bounce back once the ice has melted, and instead are bent permanently toward the earth, “trailing their leaves on the ground/Like girls on hands and knees that throw their hair/Over before them to dry in the sun.”  The birches remain forever bowed, and their leaves, instead of surging upward toward the sun, stretch along the ground for that same nourishment, a stance which, like the girls on hands and knees, is merely another natural interpretation of their own range of motion.