In order for a tree to thrive, it must have soil that is permeable to water and gases, most akin to the "spongy" soils you often encounter when walking in the forest. On urban sites, we frequently see soils becoming compacted through walking, mowing or even vehicle parking within the root zone of trees. This compaction can become greatly exacerbated when sites with trees are developed or redeveloped, without adequate tree protection being installed, due to repeated heavy equipment traffic, particularly in wet conditions. When the root zones of trees become compacted in this way water and air penetration is reduced and the trees slowly decline, finally succumbing in some cases years after hand-over, leaving a liability with the new owners or operators.
While protective fencing in the above example would have been preferable, the use of de-compaction tools, such as the Air Spade, can greatly help to remediate compromised soils and greatly improves affected trees' chances of survival post-development.