I found the email I got from Dr. Bors on 7/1/14. Here’s an excerpt that might interest you:
“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.”