Here is the last paragraph from his email dated 7/1/14:
For best longevity one should grow the cherries as bushes with multiple trunks. Using renewal thinning you should get rid of a trunk or two every year or two to allow new ones to form or let suckers in the row come up to replace them. Our original seedling rows are 22 years old and are still alive and fairly healthy. On a severe -50C winter, we didn’t lose trees but we lost the oldest trunks of most trees. Specifically it was those branches that had born fruit for many years and were hardly making any growth. Perhaps a trunk should be removed somewhere around 7 years old? Maybe 10? I’d think the bushes could go on for many decades.
So if I interpret that correctly, you’d remove a trunk or two every year or two after maybe year 7 in the life of the bush.
Again, my CJ’s have been heavy croppers the past couple years but at this point the oldest/biggest bush (at least one of the 3) looks fairly barren on the lower interior branches. That is not something I’ve ever noticed before to any great concern level anyway. But I do wonder if a combination of heavy bearing and maybe lack of sun have been contributing factors. It just can’t be our Iowa winters on these zone 2 bushes. I’ve not had any winter-kill to speak of on CJ’s, but the CP’s may have. Though on the CP’s it could also be a byproduct of a weakened immune system or something. I’ve thought for some time that the CP’s suffered from a vascular problem, but they my well have never recovered from the cherry leaf spot they each got a couple years ago.
Anyway, hope this helps.