Our first extremely common issue to consider is the fact that your trees may be growing in compacted soil. Since you most likely spend a lot of time outside, especially if you have kids, your soil is being compacted by playing, walking, running, etc. Your soil is getting quite a bit of foot traffic, on top of any heavy machinery like lawnmowers or construction projects that may be going on. Also, if you have a newer house, a lot of soil compaction will have occurred during the building on your home.
Why is this an issue? Compacted soil actually leads to restricted root growth (which we will discuss in more depth later), as well as crushed roots, and/or stressed soil. There are some fairly simple solutions to this problem, luckily. By manually loosening the soil, you are reducing the compaction and strain on your trees and their roots.
You can simply mix in organic matter to loosen up the compacted soil, or you can try vertical mulching, which replaces the soil in the root zone.