This is a very fun project I didn't start early enough for my kids to actually get to use as a jungle gym! I would like to encourage more interest in this sort of a project for kids - imagine a living play ground! I feel it would be healthy for kids to consider actually building a tree house out of living trees; about what it would mean in learning patience, and about learning how a tree grows.
This Box Frame project has been a particular challenge as the four trees were not the same size, age and caliper, ie; diameter, when planted. (They were left over from another project and hurriedly put in the ground in a square.) Consequentially, the exercise through the years has been to always try and equalize the stages of growth: side to side, corner to corner. It's a single tree now, about a nine foot cube, with four trunks feeding and supporting it.
I've explored many ways of shaping these trees during the course of this project. I appreciate every project for the learning process. I will describe my latest intervention starting with the problem I was facing. Because a trees' basic, obvious, growth strategy is straight up, one of the corner uprights in this piece (right over a corner tree trunk,) got enormous and dominant very fast. Not much growth was going towards completing the other growth that I wanted to accomplish out on the side. The tree, because it is a tree wanting to grow straight up, wasn't interested in sending nutrient energy growth out to the side and then up.
Soooo.... I removed three quarters of the upright corner post, leaving a literal pie shaped quarter of that original column. The remainder won't take so much energy, and I'll get more growth out to the side. I anticipate the wedge shape upright will heal over with new bark in 2 or 3 years.