Shear plane cracks

Shear plane crack on a branch (Honey locust)

I actually don't encounter shear plane cracks very often, relative to the number of trees I've inspected over my entire career. I think these branches usually fail entirely and end up as hangers, which is a broken branch suspended in the tree, still attached by some tissue. So, a shear plane crack means a failure has occurred, but it didn't fail entirely or completely.

The ISA TRAQ manual describes that these cracks occur when the top of the branch is moving one direction and the bottom is moving the other, and that makes sense. But the manual also suggests that now that the crack has formed (the failure has occurred), the tension has been released, and that often the branch will grow over that (the tree's version of 'healing'), and you should strongly consider leaving that branch instead of removing it.

That's right where my opinion diverges from the authors of that manual. Unless there is a really good reason to leave that limb, I'd argue to remove it. Good reasons to leave it could be the branch is really important (e.g., large percentage of canopy, aesthetic reasons, privacy screening importance). In my photo shared here, I'd be afraid of this crack continuing to expand backward toward the trunk, and now instead of a nice clean cut we have a tear/rip. I also have a problem with the foundational assertion that many of these cracks heal over - I think there is some error in that assumption because, as I said, I believe most of these cracks fail and become hangers, and it is actually quite rare to see these branches remain upright. So there is some sampling error baked into that assumption, and I say assumption because no one has ever done any real research on this topic. Show me some data, otherwise it's just anecdotes, and until that time, I will err on the side of caution and remove most of these failed branches.