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I don't have any helpful evidence Mario, but I think an important question is: What specifically is being separated when bark is damaged in this way? I would think that the vascular cambium and the phloem are separated but I'm only supposing.
This interface that easily pops apart seems to be common to most species. My guess would be once this separation occurs, the bonds that join the living tissues are severed and cannot 'heal.'
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The insight that everyone is asking about requires us to understand what the cambium is and what it does. I'll state again that I'm making no personal comments on anyone, but we have to again suspend our disbelief and look critically at the dogma and the clichés that keep us misinformed.
The illustration below is from Gilman and I'd like to use it in helping to explain the many perceptions and impressions about what goes on under the bark of most trees.
The red cells are the cambium that I call the gossamer engine and I have tried to explain for many years that a perspective that understands the importance of cambium and its functions, will make a great deal of difference in how we think about, and what we do to trees.
When I talked about “microsurgery” on problems like included bark, I was explaining a technique for 1. Minimum intrusion and wounding, 2. Minimum exposure to pathogens and elements, and 3. A basic concept that once the two separate woody cylinders of included bark are reconnected as a single cambium, the tree will never go back again to that condition of included bark.
That included bark will be left behind as a defect and we can pridefully expand our roles as stewards using new techniques that fit into Alex Shigo's discussions of Modern Arboriculture. (With Mario's permission, later on I'd like to use some of his photographs to illustrate the correction processes that trees do naturally and we might have overlooked.)
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As I said, the red cells are the cambium and Gilman and I are in agreement that the cambial layer is extraordinarily thin--I describe it as one cell thick which is the opinion of many scholars and I will concede that nature is wet and sloppy, so she can have a few cells out of sequence in development that can constitute a cambial zone.
The cambium is a magical place where those red cells can be considered to float around in a liquid and push quietly sideways and forward between the hardening walls and structures of the dedicated xylem and phloem produced as daughter cells. Think of it as a smear of Jell-O in between two sets of types of cells that are being strengthened with lignin and cellulose that will never divide or rmove again.
As the phloem and xylem mature, they strengthen and are cemented together by all of the chemicals and products described in textbooks that make up the A, B, C, or D questions given in tests that we all hate, or at least I did.
I suspect that if we had a perfectly circular tree trunk out of dormancy, and cut it all the way around at the top through the bark and then cut that section again 12 inches below, we would be able to grab it with two hands and rotate the section as a band of bark. Everyone already knows, with the appropriate blade that we could cut a square out of a bark, take a look at its underside, and stick it back in the hole. Minimum cut, minimum exposure, and a couple of nails will keep it in place. (Mario would be pleased that I'm endorsing simple nailing back in place as a perfectly valid and practical technique.)
There have been many experiments where a square of bark was cut out of the trunk and then rotated 180° before being placed back, which implies that the xylem and phloem would be transporting in the wrong directions. But not to worry, when experimenters would go back to examine the misplacements, the tree would've already figured it out and the flow directions would be corrected.
Let's also go back a number of decades where the method for determining if a tree had come out of dormancy was to cut a circle of bark with a hole saw and attach a little lever that could be tugged at by inquisitive scientists. If the circle didn't move, the tree was still dormant. When it moved by twisting at the lever, that was the proof that the cambium had regained its semi-liquid state and was prepared to get back to seasonal work.
My point here is that the cambium zone is a place of natural separation used by scholars twiddling circles, or car bumpers saying, “Watch this ! ”
(As an aside, I'm not sure that I would call the cambium an interface as in the quote because that introduces other distracting themes and considerations in the mechanical or digital worlds. Again this is not a criticism, after all I described it as a smear of Jell-O.)
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So it's pretty much established where a separation will occur, and it's likely that the velocity and power of a car bumper can peel off a considerable amount of bark whether or not the gossamer engine is in dormancy. But Mario's opening question included, This is what I found, and this is what I did in my thinking; is there some outside support for what I hoped to achieve?
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Back when I was at the Chicago Park District, I photographed one of our arborists attending to a tree in the Soldier Field parking lot that had a big chunk of bark knocked off by a car with a celebrating occupant at the home of Da Bears. What the veteran arborist did was the classic repair; cut the loose bark back to solid bark, trace, and throw all the old bark away.
I took the pictures because I was trying to understand the philosophy and the repair techniques, and later came to the conclusion that I didn't like them at all. I began to think of them as dogma and rote, and myy arborist was sincerely trying to correct the damage by making it easier for the tree to recover the damaged area.
As I now think of the problems, I absolutely agree with Mario's nailing the still moist section back in place and securing it to the xylem surface. There's an excellent chance that the cambium can be reestablished over that area that is in the natural environment for cambium growth. I also would've nailed all the other pieces in place, doing the best job I could of fitting them tightly against each other to minimize the places for outside intrusions of the elements and pathogens.
The arborist in my photographs discarded all the bark pieces, mostly because they had been desiccated and heated by the sun, and by the time taken between the accident and his being assigned to deal with the problem. Saving the pieces weren't part of dogma.
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Okay, let me mutter about the conditions and processes as I think I see them:
If Mario replaces all the bark as tightly-fitted as he can, including the one he saved, they will be remoistened by the routine transport of water as the trunk continues in its usual business. Even significant bark desiccation will be significantly corrected by the ever-present movement of water through the symplast and the apoplast. Again re-wetting will be maintained except perhaps at the joint lines where there is a space between adjacent pieces of bark.
As I've been told in some texts about this kind of wound, cambium generally goes along with the bark. I don't know if that's true or not, but it's reasonable, so I'll assume that most of the cambium is stuck on the bark exposed to the sun and air, and won't live very long (?). If that's the case, where do I get the feedstock for new cambium? The cambium will have to theoretically grow in from the edges of the wound as is the dogmatic expectation of chisel and trace.
Well here's where I think the magic comes in. With what Mario did, and if I told my arborist just after the accident to put all of the pieces in a plastic bag with some water and keep it out of the sun, I will have slowed or stopped the desiccation and had much better material for re-nailing.
(I've also never understood why black plastic is the choice of experimenters or the lecturer. Why would I keep the things that I wanted to stay alive in a black solar cooker?
I use white plastic. If sun-scald exists as we describe it, why would I want to further introduce heat to the injury?)
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Another okay. We all know it will take a long time for the damaged area to be covered through the process of growing in from the sides, top, and bottom.
Let me explain the faster process for us to be better stewards:
1. Our re-nailing has crudely reestablished the conditions and positions of the bark and the wood. Those wood and bark areas will be re-wet simply because they're placed flush against already wetted xylem. Diffusion takes care of moving water--and sugars--into the damaged areas.
2 Even if all the original cambium has completely disappeared where we re-nailed the bark, parenchymal cells are available in rays and adjacent structures. It is very likely that they will take on the initial function as space-fillers and grow into the many voids. Then because trees are totipotent, those parenchymal cells will have the ability to become meristematic and form new cambium.
3. There is no requirement that they act in any orderly fashion by our ideas of order; spotty and scattered groups will be quite sufficient. So, instead of slow, orderly growth in from the edges, we have a localized spread very much determined by the surrounding conditions to accelerate or slow new cambium growth.
4. Please absolutely remember that cadmium stays faithful to its internal discipline of being 1 or 2 cells thick. Any further division
must produce either xylem or phloem cells which never divide again after maturity and stay the dedicated cells we know as wood or bark.
This is not a bonding layer or zone. It is the reestablishment of the gossamer engine which then sets about this task of producing xylem to the inside and phloem to the outside. Once established, those two different kinds of x and p cells take over their expected functions. They will continue their jobs throughout their lives until xylem reaches it's pre-programmed death, generally dictated by species, and the phloem is crushed in creating thicker bark.
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PS: To me, the design of the storied vascular cambium in a number of species of trees is staggeringly beautiful and smart. I have built my own perspective about trees around the gossamer engine, and as I have said before, if the cambium hadn't been there to create the woody cylinders, leaves would've had to be hung on spiderwebs
Tubbs
