It's well-known, at least among tree care professionals, that tree roots can only grow where there's enough oxygen for them to survive. In most situations, this means that almost all roots of even very large trees will be found within a foot or so of the soil surface - especially where heavy clay soils are common, above.
It's equally well-known that the roots of many trees extend far beyond the "dripline" of a tree. In fact, through tedious excavation work by researchers, it's been shown that the roots of some large trees can extend well over a hundred feet outward from their trunks!
Therefore, any construction/excavation activity within fifty feet of a large tree will damage its root system to a greater or lesser extent - itís simply unavoidable.
The types of damage can include excavation that cuts through roots (remember almost all roots are within a foot of the soil surface), stockpiling of soil and/or addition of "fill" that buries roots (just like putting a plastic bag over your head, that's not a good thing), at right, movement of bulldozers, cement trucks or other heavy equipment that crushes shallow roots, below left, removal of bark and/or any combination of the above.
Obviously, the closer to the trunk the activity occurs, the more extensive the damage is likely to be, below right.
Depending upon the extent of the damage caused by construction activity, the affected tree's canopy (leaves, stems and branches) may become less vigorous because damaged roots canít deliver sufficient water and nutrients.
As a result, the stressed canopy loses its ability to produce and transport sufficient plant food (simple sugars and carbohydrates produced through the process of photosynthesis) back to the root system to repair damage caused by the construction activity.
This vicious cycle of limited water, nutrient and photosynthate transport often results in a very gradual decline of affected trees. They often become both an eyesore and hazard long before dying ten or even fifteen years after completion of construction.
It's this scenario that often leads me to explain that homeowners building on wooded lots often pay five times for their trees;