Arboromega asks a good question. In my job, these days I am usually pruning trees that are 5-20 years old. Grown most often from crappy nursery stock. Though some of the pruning is to remove broken or crossing branches...I put most of my energy into creating some form of a central leader in a tree. I could tell you a lot about what I do, when and why...
this is their specs, they know what its going to look like as theyve done others (ive done some for them). no they are not planning to remove the other 2 leads as thats most of the canopy. im trying to figure out for my self why is this practice being used? making topping cuts (they really are) and removing food source from the tree for what? most bad unions dont fail
You are right- most of what we call "bad" unions DON'T fail. BUT we do know that there is a higher rate of failure among bad unions and strong unions. When I see a bad union, I never say there is a high chance of that failing- I just point out that there is a highER chance of that failing (some report 2x more likely to fail than a good union).
So we are removing a large amount of food producing foliage/canopy to reduce the chance of future failure. Like losing a finger to save your hand or something like that.
I think tree species is pretty important when considering if a bad union will fail. Siberian elms and willows seem to fail at a much higher rate than other trees around here. I have only seen cedars fail around here from root failure and not bad unions. Multiple topped cedars here seem to do alright.
ill try and get some pics when i go down there next week. most of what they subordinate are conifers, red cedar, redwood, spruce, havent seen it on a pine yet. a cable seems like a much better fix mostly. to me anyway.
The hard-and-fast rule of a central leader fails most of us when it comes to trees that are post adolescent, regardless of their size.
Once a tree has been allowed to have 2-3 central leaders, the decision to reduce it becomes severe at a certain age. Conifers seem to handle the 'pruning' better than most >>> they will simply react by either a central leader (leave alone) or multiple leads (take your pick).
Cabling is an option, for sure.
Gosh, what about leaving well enough alone ? Let it be what it is. We can't "fix" everything, ey ?
After further thought, I would also add that the age of the tree is very important in whether I subordinate competing tops of trees. If the tree is young, I have no problem doing it. If it is a mature tree, I am far less likely to do it.
Funny thing is,
The definition of 'excurrent' & 'decurrent' changes with the age of the tree.
So you cant really say a particular species of tree is one or the other.
An accurate statement is:
"A tree can exhibit excurrent or decurrent characteristics".
Frans, regarding the age of the tree...most of the trees we plant are ones that will be decurrent when mature. For the first ten years of their life, we prune them to have excurrent structure to encourage proper scaffolding branches and all that jazz. I know that as these trees mature, they will sway from excurrentness, and that is fine.