Why do we need to be concerned about compacted soil?

Most tree roots are less than half a metre below the ground. Structural (woody) roots hold the tree up and consist of bundles of fibrous roots, which are very small and fragile, absorbing water and nutrients from the soil. These fibrous roots cannot survive if the ground has been compacted: soil-pores are destroyed and so air and water cannot filter down to the roots. In this case, a tree will very quickly suffer as it can no longer translocate dissolved nutrients and water to the rest of the tree; the tree stops functioning and dies.

Tree Roots and De-Compaction

(A) Tap Root : Provides main support of tree and anchors it firmly in the ground (not all trees have one)
(B) Lateral (Structural) Roots : Support and anchor the tree; may extend far out, beyond crown spread.
(C) Fibrous Roots : Masses of fine feeding roots close to ground surface.
(D) Deeply Descending Roots (‘Sinkers’) : Grow downward from lateral roots and also anchor the tree.