Trees vs Sidewalk

I'm walking down the street one day. It may have been the very merry month of May or June or September. I don't remember. Suddenly I trip and stumble forward a couple of steps. Immediately I do two things. One I looked around to see if anyone saw me. I don't know why. Maybe it's less embarrassing if no one has seen me. I also turned around to see what I tripped on as if something suddenly appeared. I noticed a break in the sidewalk that caught my shoe. I also noticed that the roots from the tree that is planted between the street and the sidewalk have pushed up on the concrete causing the trip hazard.

Tree roots grow mostly close to the surface where they can absorb the water and oxygen penetrating the soil. When trees grow in the woods where the soil is loose water and oxygen can seep into the ground allowing the roots to grow down and outward. This allows for maximum growth of the tree. In an urban setting the ground beneath the sidewalk is compacted in order to keep the sidewalk from settling. Makes sense. But that compacted soil doesn't allow water or oxygen to penetrate into the ground. The roots instead stay close to the surface just under the sidewalk. They eventually push up the sidewalk causing a trip hazard. As a result, cities have to spend a portion of their budget on shaving or replacing heaved sidewalk sections. Compacted soil also stunts the growth of a tree.