Included bark in a tree's crotch has a serious weakening effect, but there are things you can do about it.
(Continued from Tree Repair - 2)
After all that anatomy we are now ready to think about included bark and how dangerous it can be. Let's look at the branch collar again and the BBR above it. Suppose the branch is at 45 degrees off the trunk, a good strong branch aiming slightly upwards with a well formed collar and BBR. Now if we could decrease the angle so that the branch came closer to the trunk, a number of things would happen. First the top of the collar and the trunk would be pressed together, beginning to form a small pocket. As we further decrease the angle, the BBR would be swallowed in the tighter enfolded pocket forming between the branch and the trunk. If we again further decrease the angle, not only will the top of the collar but the BBR and the inside bark of both the branch and trunk would now be touching and will form a deep pocket of bark included between the branch and trunk. This bark pocket, that has little of the natural strength and holding power of a well formed collar, is now an included bark crotch and the branch can easily be split off from the trunk.
Most tree branches that are damaged in storms are included bark branches. If you inspect your trees and find these problems, prune the branch off. If you can't live without it, if it would strongly affect the shape, there are other options.
One is bracing, installing a threaded rod, or on the micro scale a deck screw, through the bottom of the crotch. It will supply the holding power that nature did not. Another is to prune the branch in such a way, through thinning, and overall reduction, that the branch’s natural vigor is reduced, its growth is inhibited to some degree. Then, as years pass, the trunk collar will start to grow around the branch, getting a better grip and reducing its splittability. This will take a number of years.
You now have another powerful and useful tool, included bark, like the story of the bud scars, to take to the nursery or garden center. Now you will never buy a plant with included bark crotches.
(Continued in Tree Repair - 4)