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:
A while back, I posted some photos of how my American beech (Fagus grandifolia) is getting along with recovery from the wound I inflicted upon it.
I had decided that there was risk of included bark developing between an already large branch and the trunk of my beech tree, so with considerable ambivalence, I removed the branch. That left a large wound on the tree, which I understood would result in some rot within the trunk, but then again, trees can be wonderfully adept at compartmentalizing decay.
Here’s an illustration of the barrier zone that a tree can construct, via internal alterations in the chemistry of its cells, to wall off infection from otherwise healthy wood inside the tree:
What I have been watching on the exterior of my beech is the slow growth of what’s initially called callus tissue and later, as the callus becomes tougher and stronger, woundwood. The hope is that this continuing growth of woundwood will ultimately seal off the interior of the tree from further exposure to organisms that cause decay.
As you can see, the tree is making good progress. I’d tell you that I’m really proud of it, but then I don’t want to encourage any vanity in my beech. It’s already the queen of the backyard, and the red maples, tulip poplars, and pecans all know it.
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:
If you happen to be a tree, one of the bigger challenges you have is this: I need energy to grow and reproduce! So I’m gonna reach for sunlight, water, and nutrients. But how far and fast can I reach before something like this happens?
The photograph above shows an American elm (Ulmus americana ‘Princeton’) planted years ago by Tree Watch and Trees Atlanta in Freedom Park.
American elm is really great at reaching. It can grow fast. When it’s at home — ‘home’ being rich, alluvial soil in a forested floodplain along a river or stream — a tall American elm will have channeled so much of its energy into growing upward, in order to reach that lovely sunlight at the top of the forest, that it may have no branches at all until the 50- or 60-foot mark.
Of course, an American elm growing in an open, grassy section of Freedom Park has no difficulty at all accessing sunlight. It’s like a kid left alone in a candy shop. (Think of that poor elm tree in Freedom Park as a kid with a terrible tummy ache.)