Back to the original question:
Can someone explain to me why some plants can be barerooted with no problems and others will die?
Why do some die? Because the roots are damaged too much and these species
don't have the energy/force/capacity to regrow them.
Why do some live? Because the roots are damaged and they
do have the energy/force/capacity to regrow them.
How does the plant "know" it's been barerooted?
Because it loses nearly 50% of all fine hairy roots, it loses close to 90% of all connections to mycorrhizae (and they'll make sure to inform the plant by hostage takeover, they might be symbiotic, but they'll still choose their own survival over that of the plant.. Law abiding citizen gone rogue). Suddenly there's more air, a different environment. It's like having a pack of functional gills slapped to your back and being thrown in the water. That's quite a drastic change of environment! I can imagine a tree coming from nusery soil to a aerated bonsai soil will feel the same way. How do you respond to being underwater? Do you unzip your pants if you have to pee underwater? Nobody taught me this! All kind of new questions arise and some plants need time to answer them. Others know the drill and just go with it. And some don't even care and just do what they always did.
Why is there a grey area in between?
Because nobody writes down if they snipped off all root tips during their raking/shaking/washing procedure. They don't count the couple of thousand roots they damaged, it would take a few days. They can't see the fine hair roots, so they can't see how much they are damaged. Our eyes aren't good enough to do so.
Also, because people have different visions of what a bare root is. Others snip off large portions of roots while others don't.
That's where science comes in. Scientists are weird people, they seem to like counting and logging this kind of stuff. They then produce literature for the world to read. Awesome! We should use it.
Now the actual question is, how do you get out of the grey unknown zone? Not all information is
easily available. Well, it is easily available.. Someone just has to type a bunch of words and press 'Post Reply'. But information is not always correct AND easily available. We kind of want both, right?
This is quick guide I tend to follow in all plant settings. The amount of information is like an upside down pyramid, starting with a bunch and leading to a single answer at the end.
Look up strain specific information about cuttings or propagated plants to begin with. Do they change with age? Do they root easily? -> google scholar, keywords: propagation, vegetative, reproduction, auxin, micropropagation, multiplication, cutting, and so on.
Look up strain specific information about general growth habits. Do they change with age? How do damaged parts respond? -> google scholar.
Look up strain specific experiences about timing, repotting and related techniques. Did others have success? Why (not)? -> bonsai nut and other resources.
Look up after treatment and results of those techniques. Was there something special that the person did, or just regular watering after? How did this increase/decrease survival? How much was removed and HOW was it removed? -> bonsai nut and other resources.
Look up the pitfalls, the deaths and the survivors. Is there something you should or shouldn't do? -> bonsai nut and other resources.
Is there a general thing to do that increases overall survival of rootwork on any species? Yes, yes there is. Many things. Gardening guides are full of them. Use that information, hybridize it to bonsai. Other things sound so logical, we sometimes forget about them.. Like leaving as much roots as possible, or doing a HBR instead. -> bonsai nut and other resources.
Look at your plant: Is the plant healthy and is it the right time? -> garden.
Go with the safest technique and report back to the world so they can copy your doings. -> bonsai nut and other resources.
In general, I tend to use heuristics to see if a technique can be done. Heuristics suck, but they're easier to work with than statistics! One person doing 1 technique on 50 maples, counts as 1. Twenty persons doing 1 technique on twenty pines, counts as 20. It filters out the 'professional influence' factor quite fast.
If deaths < 5 AND survivors > 5 THEN go ahead.
If deaths > 5 AND survivors < 5 THEN stop and research why or look for another technique from start.
If deaths = survivors THEN hybridize with other techniques in a logical sense to improve rates OR pick one and go for it. This takes a body of knowledge or a body of guts.
If you use that schematic nothing can be overlooked this way. Assuming at least, that your heuristics are based on different people.
There might be adaptations possible, you can raise your heuristics range to 10 or 100 if you want. Or use statistics.
But a plan has to be solid, no matter what. If you can't explain to yourself why you're doing what you're doing and why you're doing it like you are doing it, then you shouldn't be doing it. Unless, of course, if you're the first one ever to do it. Then you should do it on one plant, and not on another. Write down the difference and report. This adds up to our numbers, which we can use in our heuristic analysis. Everybody gets better.
"I want to take a risk" or "I couldn't control myself" are solid reasons to do something in my book, but be honest about it at least. ;-)