It’s not common knowledge, but tree roots need air to survive. When the pore space around roots becomes so compacted the roots don’t get air-(also inhibiting water uptake)-the whole tree can die. It’s not always a case of trucks and heavy equipment causing the deadly compaction. It can also happen with foot traffic. A well-used footpath can be as hard as concrete. One of the best remedies for soil compaction is radial trenching and vertical mulching. Basically this involves drilling holes beneath the crown and filling them with mulch. This is an excellent way to uncompact the soil without damaging roots. Soil compaction is a fairly common killer of trees and worth keeping an eye on.