JOA V28:#6
WHICH COMES FIRST, THE ROOT OR THE CRACK?
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ROOT GROWTH BENEATH SIDEWALKS NEAR TREES OF FOUR GENERA
http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=63&Type=1
Here is my take on roots and structures.
In situations where there are butress stuctures, then the tree can cause heaving of slabs and curbs.
O2 (free oxy) is the biggest limiting factor for root propigation/colonization. H2O is the second. Anyplace where there is a leak in a structure there will be more aeration of the soil. Be this a side walk, basement floor, or sewer pipe.
Roots are dendretic structures that will "explore" the surouinding area, if one path leads to better pastures, then it will increase its carrying capasity. A leaky sewer pipe creates a plume of aerated, nutrient rich wate, so the trees grow towards it.
A cracked foundation, and draintiles will do the same.
Under engineered asphault lots with heavy traffic fracture and allow aerated water to penetrate, wich allows for woody root development. The the roots forma supporting structure for small areas of the lot and the rest sinks around them.
But this is all mot for your needs. The severing of roots will not kill the tree automaticly, but will increase the chance of failure. if decay is introduced through the wound then the support structure is gone. Failure of this sort is usualy towards the lost root, much like trying to stand without any toes. Roots are more lie props then anchors.
At two feet the chance of decay is rather high, so if it is done then the trees should be on a periodic monitoring program. At the very least, put the recomendation in your proposal to CYA incase of future failure.
The short answer to your question as to wether it will harm th trees is "It depends..."