THis is the point that is most pertinent here. I said that from the beginning. Trees--given free root run and no restrictions--do grow over the wound--eventually. It's that "eventually" that can be a sticky issue, though. In a container, or even in a growing bed, this time could be measured in decades. Some might do it in a few years.
Yes, I agree. Creating large wounds on a tree, and the subsequent callus tissue that results from it, has a very different effect on trees with very different age and growth rate.
So, the more mature the tree, the more lasting the effect. Fully grown, mature trees in nature, can suffer the ensuing damage for a very long time, if not for the rest of their lives. That's because the trunk will not thicken enough to cover the wound.
And this is why a young bonsai material, that will grow and thicken in the ground within a very short time, can be subjected to much more drastic techniques than what a more mature tree could survive. A young whip that will double, triple, or quatruple in trunk size within less than a decade, can be subjected to almost ANYTHING, as long as there is a little thread of live vein left to transport water and nutrients. This includes stripping, knotting, covering with wires and leaving them on, stomping and jumping on them, electrocuting, setting them on fire, and other exotic forms of torture (see the handbook of the Spanish Inquisition for a full list of techniques). The only limit is your imagination.
So, there is a sliding scale of what you can safely do, from a young whip to a very old yamadori. There is no hard line in between, but in general, as you slide towards an old yamadori, you can do less and less, erring on the safer side.
And this is why, one can safely leave on a wire, when working with a juniper or pine seedling. It's just another form of wounding the tree, which creates budges, twist and turns, and potentially, add more character (the result being subject to personal taste). The seedling will quickly grow over it, and resumes its healthy growth. Of course, there is a point where even a young whip will not survive, so one needs to understand how much he can do.
At the end, some people will like the result, and some don't. If poorly done, the spirals created on the tree can look very artificial,and there is a big risk of reverse taper. So, if you do this, you better work simultaneously with a number of seedlings, and after a while keep the few good ones and discard the rest. It's hard to control the volume of scar tissue created, so some of them will not look very good. On the other hand you can also correct the faults later, with jinning and shari.
But I don't see too much of an issue on the horticultural side, becuse we are talking about very young trees. You don't use this technique on old ones.
