Actually, if you saw the first pictures, the cables don't actually "touch" any tree (this is the smallest pine at the low end): https://c3.staticflickr.com/3/2944/15188634078_2b3de04150.jpg
What we did was attach two-by fours to the tree, and then wrap the cables around the two by fours. https://c4.staticflickr.com/4/3870/15188634228_37f45d19e2_c.jpg
Dunno if that will "protect" the tree or not; but that's why we did it that way (in theory).
You'll notice we doubled the cable at *both* ends also, so that there are always *two* cables at all points, even around the big tree where there is no cable joint at all.