The wilds of the woods; have naturally the ruthless competitions, for space, food etc. that only allow a few of the best to survive, as other jungles.  This maintains the strongest, luckiest, most dominant within a species.  As a limiting feature, when trees are tall enough to be drowned in light, they have more of a codominate fault; that sets the strength of the physics of support against itself.  The house divided, does not stand as well, and the codominates split, limiting height etc.  Too much mulch can be bad, too much water; even too much light.

In an urban setting, it is  more prevalent to have lower areas of the trees flooded with light, that cause more codominate joint faults; at lower points, that will get more food at larger joints, and more leveraged length.  So this codominate fault, can happen at the top, lower in the tree, even at the ground level as/ virtually as another tree 'siamesed' against.  All have the same structural faults that a tree generally seeks to form the opposite of.