So, yesterday I was walking northeast on the section of the Freedom Park Trail between North Highland Avenue and the Jimmy Carter Library & Museum/The Carter Center.
Years ago, we planted trees nearby, along what is now called John Lewis Freedom Parkway.
These are winged elms. “Winged” refers to the corky “wings” or ridges that can be found growing on opposite sides of the tree’s twigs and branches, particularly its younger branches:
(For this tree, by the way, the scientific name and the common name are a perfect match: Ulmus alata is literally “winged elm.” Contrast our water oak, Quercus nigra, which we should be calling “black oak,” I suppose. Except what we commonly call black oak has the botanical name Quercus velutina, literally “velvety oak,” referring to the fine hairs found on its buds and young leaves. What a nomenclatural mess!)
I saw that one of the winged elms along the parkway has split in two:
The UK arborist I mentioned there, Dr. Duncan Slater, has done extensive field work to document the conditions under which bark inclusion appears common.
It shouldn’t be a surprise.
If we start from the premise that, in the same way that our physical strength is developed by the strain we put upon our muscles, tree “strength” is developed in part by the strain that gravity and wind put upon wood, it makes total sense that anything preventing a tree from experiencing that strain can be detrimental to it.
And often it happens that a tree will be naturally deprived of that necessary stress or strain.
Slater calls these “natural braces.” For example, a branch from one of two equal-sized trunks of the same tree — these are called “co-dominant stems” or “double leaders” — may fuse with the second trunk. Obviously, the two parts of the tree are more nearly frozen in place. What Slater has discovered is that under such conditions, the junction between the two trunks is more likely to be weak due to bark inclusion.
So if that’s true, it’s obviously very important to eliminate a natural brace when a tree is young, but if a tree with a natural brace is older, cutting out a natural brace may be a recipe for disaster, i.e., a tree service may be increasing the chance of the tree splitting and falling on someone.
And look what I found recently in this Freedom Park oak with co-dominant stems: