Respect the Crotch.

Much of what we do as arborists deals with branch unions, from setting our climbing lines, to making pruning cuts, to installing cables and braces, to hanging a block or pulley to even just standing still for a minute to take in a breath and the wonderful view. How often though do we take for granted how a branch is formed off the trunk and how special a mechanism this truly is.

I'm not sure how many collar cuts I've made in my life, but what I do know is that even though all branch collars are formed in the same biological process, rarely do two collars look exactly the same. A good place to start understanding the branch and it's attachment is to understand the anatomy. For this I turn to Shigo's Modern Arboriculture:

"As branch tissues develop toward the base of the branch, the tissues turn to form a collar. The trunk tissues begin to form later, and they circle the branch collar with a trunk collar. The new branch collar fits over the shaft of the tissues in the existing branch. The branch and trunk tissues develop connections below the collars...Many times the collar-forming tissues mix with each other and the collars are not distinct." (page 86).

By this excerpt we can see how strong and reinforced the tissues are in the branch collar. This is critical to understand from a climber's perspective, because having a climb line seated perfectly in a branch union will give us the strongest anchor available biologically speaking, aside from tying directly to the trunk itself. Technically, Shigo explains, branches aren't structurally attached to the trunk per se:

"Just as branches are really not structurally attached to trunks, neither are roots structurally attached to the tree base. The small strip of branch tissue below the branch cannot be considered a structural attachment. The holding power of roots and branches lies in the series of collars," (page 87).

 We can therefore see how important it is to target those branch collars when building our anchors. The further we move out along a limb, the further we increase leverage on the branch union, and the further we raise the chances of that branch failing. Seek the collar!

Let's move on to pruning. Earlier I had stated that no two collars look the same, which may be a stretch I'll admit, because every branch collar, microscopically is formed in the same place on the tree and is comprised of a few different things: the branch protection zone, the branch bark ridge, the branch pith, and the actual collar where tissues from the branch and trunk build upon one another.

For pruning purposes, it's important to understand the branch protection zone. A proper pruning cut will land itself perfectly in line with the upper and lower points of this protection zone. Shigo makes it clear that not all branch collars will look the same, some will be more defined while other will be flatter and almost seem nonexistent (page 93). To understand the pruning cut, you must understand the branch collar and how it is built.

This is information is not new. Even when Shigo's book was published in 1991, and excerpt states:

"Much of what we think is new was known many years ago. In 1754 researchers knew that the collar should not be removed or decay would develop rapidly. The protection zone on the branch collar was well understood one century ago. Then why did the flush cut persist? Mainly because of one word-healing. Everybody thought that the large ribs of "callus" meant strong "healing". Now we know that what they called callus was really woundwood," (page 91).

Even with all the information we have in a rapidly changing and technologically advance world, information can still be misinterpreted. It's important I think to constantly re-evaluate what we do as arborists and why we do it. Shigo tell us that many advances is science came not from discovery but rediscovery (page 91). Maybe the moral of this story is not how many pruning cuts you've made in your career, but how well placed they were. Afterall, it's our job.