Maureen Sexsmith-West ISA Certified Arborist, PR4600A The most important and least considered part of your tree is the root system. The root system of your tree will be extensive (several times wider underground that then tree is tall). The majority of these roots are absorbing roots that occur 6-12 inches below the surface. The structural roots which are the branches underground, grow as the support system to the tree.
The presence of suckering on some varieties of trees can be an indicator of root issues.