Q.bark falling off my pecan tree
I have noticed the bark on a very large pecan tree is starting to peel & falling off??

Some barking sloughing off is normal in trees. There can be more serious causes.
Examine the tree for signs of pests, as they can attack the bark of the tree.
Drought can cause stress to the tree.
Poorly draining soil can cause Cotton Root Rot.
Crown Gall can also attack the tree.
https://www.gardeningknowhow.com/edible/nut-trees/pecan/growing-pecan-trees.htm