While walking along a local neighborhood landscaped area, I caught a glimpse of an interesting tree regrowth phenomenon. A tree had been recently cut and new trees were regrowing around and in the stump. There were two new growths growing directly on the stump. If you look closely, they were growing on the outer portion of the stump. They were growing straight out vascular rings of the living tree. The new tree was utilizing the roots system of the old tree for its water and minerals. The other trees growing near the old tree stump were growing directly from the roots. The tree “senses” a loss of photosynthetic material (leaves or needles) and tries to make up for that loss by putting energy into creating new growth. You can observe this sudden growth when a tree is overly pruned, new shoots of green suddenly sprout everywhere.
Notice that the vascular system of the tree is the outer section of the stump just next to the bark, this is where the xylem transports water and minerals to the leaves and the phloem takes the sugar produced by photosynthesis to the roots and other parts of the tree. The inner bark becomes hardwood which supports the tree. Cutting the vascular layer can kill the tree. New trees don't have a very thick layer of bark and a simple edge clipper using nylon fishing cable could penetrate this layer. Also tying the string tightly around the tree could cut into this vascular layer as the tree grows outward. Remember trees can only grow down (roots), up (tree crown and branches), and out (trunk). If an object is in the way the tree will try to grow around it.
Coastal Redwoods, Sequoia sempervirens, can regrow from their mother stumps and create new trees basically a clone of the original. Muir woods is an example of the second-growth forest of redwood clones.
Nature has an infinite urge to survive and this regrowth is an example of that. Treat your trees with care.