On the topic of pruning... You continue to prune after the tree tubes come off right? I have never pruned my trees that are 4-5 year old so it looks like I will have some work to do soon. Any low branches need to go right? Any splits should be pruned?
Can you prune too much and kill the tree?
You have to kill the root system to really kill a tree, but you can screw one up by either not enough pruning or too much. The main thing for an oak or chestnut would be to develop a strong central leader with no forks. Fruit trees are pruned differently and someone else would have to explain that method.
I watched the video and what he did to the trees, I disagree with. Not really me but Dr. Carl Whitcomb the inventor of the Rootmaker planters does.
Here is what he says on page 156 of the book Production of Landscape Plants II (In the field).
"When lower limbs are prevented from forming due to crowding or if they are pruned off prematurely, the stem development typically is like a piece of pipe; that is' the two sides are parallel."
In other words there is no stem taper. You see in the video that he had to hold the seedlings up that had been pruned when planted.They are flimsy.
No stem taper is directly related to having a poor root system and trying to drive vertical growth at the expense of the proper stem development.It is the lower limbs that send their energy to the stem and root development. He says that when the tree is finally taken out of the tube it will still require a stake because it won't be able to hold up the top during snow, wind and rain and it is susceptible to breaking, splitting or cracking.
On page 152 he says "side branches should not be pruned until sufficient stem diameter and taper are developed to support furthur growth."
and that the stem should be like a good fishing rod that spreads the weight evenly from top to bottom when bent.
If you notice the video of the trees that had not been pruned early had good strong thick stem development. I believe in waiting to prune until the 2nd year or at least only pruning lower branches by 1/3's to reduce the amount of air blockage in the tube.
I do use that same tube though and really like them.