I am in quick need of an answer as I have recently excavated to put on an addition and the excavators have dumped the clay filled soil around my Oak trees. How much soil can I add to the area around Mature Burr Oak, White Oak and not as mature shagbark Hickory trees? Also, How detrimental to the trees is it to have heavy equipment driving in the drip lines of the trees? Any info would be appreciated.
Lisa, working on the type of construction damaged trees you have described is half my business. The heavy equipment operating within the dripline of the trees has damaged the fibrous roots. We call these roots the 'feeder roots' as without which the tree has no way of uptaking water/elements. Imagine in your minds eye the damage a 10,000lb machine did to these roots that are only 10 inches below the soil line!
As for the soil they piled around the trunk: Trees roots can stand being in wet conditions for extended periods, (easy pro's, im making a point, ie, field capacity). The trunk section can not! the portion of the trunk that flares out into the soil is know as buttress/flare roots. You always want to see the 'flare' extending outward from the trunk into the ground. This soil piled around the trunk will keep that area of trunk that is buried too wet and that leaves the door WIDE open for various pest/pathalogical issues to enter.
Now, the builder you used should know about the potential problems of running his equipment over these roots and dumping soil onto the trunks of these trees. You may have legal recourse. You WILL notice flagging. Look for the tips of upermost branches to begin dying back. The damage will take time to manifest, sometimes many months, but by then the builder has cashed the check and will avoid your calls about the subject.
I hope I helped some. Good luck.