Well i seem to have merely produced more confusion rather than some clarification which was my intention, and thats definately down to me not being able to explain what I mean i quess. So I'll try to be clearer, and please note I'm not suggesting that others have said this merely that I hoope this makes my opinion on cutting co-dominants clearer...
So what I don't mean:
Pruning cuts on codominants should be perpendicular or (close to it) to the outside of the branch or limb, no.
Pruning cuts should be flush, no never.
That heartwood is dead, no its not, (but its not alive either)
That heartwood has no defensive processes or mechanisms, no heartwood does have those processes and mechanisms otherwise CODIT as a model would not be applicable.
So what I do mean: There are no collars at the union between two co-dominant stems (If it helps this is a quote from Shigo Tree Pruning Worldwide Guide pg 156) making the correct cut as described by Shigo for many of the trees I cut is very hard to pick, there are no give aways as to the bottom of the stem bark ridge.
The resulting estimate I have feared that I am getting too close to being flush, cutting into more timber than I should, so I have lifted the bottom of the cut. It is splitting hairs and reflects doubts I have about my own abilities, and if I came across as lecturing on what others should or should not make their practice that wasn't my intention.
If you as the person cutting are comfortable in the species you work on in making the cut at the "red line" all well and good. In some of the species I work on it's an easy pick too, in others it is by no means easy so I err on the side of the "blue line"
It is always preferrable to have co-dominant stems removed when they are small, when the tree is young. By the time the tree gets to the size in the original photo by Ekka the impact on the tree system of removing that codominant(if it were a healthy energy producing limb) will be to stimulate massive changes in hormonal control of epicormic buds, not just in the immediate area of the cut near the union but more often than not along the remaining limb itself. (Now that will often happen no matter where you cut, but I don't mean it doesn't matter where you make the final cut, I don't mean just lop it off cause she's going to sprout.) The epicormics that are produced are not always a bad thing for the tree, but if they are around the lip of the cut of course they will have to be removed. In some of the older trees I work on epicormics are a signal of increasing stresses sure but they are very important to the maintenance of energy levels within the tree as a whole, so I'll leave all those with no target, that I can see have half a chance of forming reasonable branch architecture in 5-10 yrs.
There is no branch protection zone behind the cut you make in the case of codominant stems there is a barrier zone that forms in the wood grown after the cut is made, but "co-dominant stems do not have protection barriers" (again if it helps that is Shigo Modern Arboriculture pg 108) So again my cutting slightly above the "red line"is about trying to ensure that I don't end up making an error that results in excessive cambial dieback under the cut opening up the limb to increased borer attack (longicorns in the case of the Albizia saman I spend so much time looking after)
Look I hope that's clearer about where I'm coming from?
SF |