Spindly spruce trees lean this way and that, looking as if they're drunk. The actual cause of this odd alignment has to do with their shallow root systems, which get readjusted by the nearly continuous expansion and contraction of permafrost under the tundra surface. Permafrost is a layer of frozen ground, sometimes more than 6 feet thick, that never thaws. Without it, much of the tundra would be completely impassable.
