Did you do a chop on all of these? Do I understand you correctly? I know there are some big time big name bonsai people, way bigger than me and what I think, that will tell you that with Pines it is important that you keep as much foliage as possible to keep the tree going. I will tell you that chopping is probably why your trees survived. When I do Mugo Pines in the summer it is alway coupled with doing everything else at the same time. I believe that it is not a balance issue, as some have pointed out, but a mutual stimulation that keeps the tree moving. I believe that if you cut the roots you put the tree in shock, and being that this is not a normal encounter for a tree it just might just sit there and die. My theory is if you have cut the roots heavly as in harvesting or doing a major root pruning in the beginning if you prune the top the tree's normal reaction is an attempt to heal these wounds and force the roots to function by doing so. Just my theory but it does seem to account for a lot of things. Funny I was dreaming about this all last night.
Vance, I came across this thread while googling info, so I must ask if you have any more data to support your theory. im headed to jack pine territory this weekend, while its primarily a scouting trip, im searching for summer collecting data on the species, which I have some personal experience data on summer collecting eastern white pine and fir from the same area but not jack pine. I have one good tree marked worthy of collection, not sure I want to risk that one for data, and i've only just looked at it, haven't inspected the roots even. I'm curious to know if maybe its possible that in summer, specifically the week of July 4th, may actually be a more favorable time, considering your mugo data. any info on the subject would be appreciated. I will be collecting 1 jack and 1 fir and hopefully a scotts this weekend for data purposes, but they will be young or uninteresting trees to study the response, but if there is any favorable data out there I may try for a decent pre-bonsai if I can get the roots, which from my experience, is very possible.