As the spring growth comes through on the ornamental trees, occasionally a problem becomes visible. Grafts can suddenly chuck up vigorous shoots as the scion decides to have another shout at outcompeting its graft, chunks of a previously pretty mutant can suddenly revert to its origin species. The scion, the root, the reversion is always more vigorous, tougher, more resilient than the elegant gardener-made filigree of careful selection stitched over the top.
Sometimes the results can be positively surreal. This is what's happened to a pretty, salmon-coloured ornamental sycamore in the local park:
You can see where the parks have tried to persuade this monster reversion sprout and/or graft sucker to give it up - a bark cut which should have stopped nutrient flow to the newly establishing canopy. But Sycamore is truly one of the toughest trees. The bark cut is healing, new leaves are visible and the sprout's trunk is now as thick as the ornamental it is growing on; which is itself showing signs of damage, dead wood and weak branches. The ornamental has leafed first, but that may be a sign of desperation. The fresh growth is thick with aphids, another sign of stress (and the mild, dry spring).
Then there is the size differential. Brillitantissimum (also known as Shrimp, for both its colour and its size) is a dwarf - it tops out at an adorable 3x3 metres. From the look of it, the monster sucker is heading for full size - and it's massive. This can't end well for either tree.
I can see why Parks are nervous about just chopping, though. At that size it might just kill the whole tree. Hence the bark cuts. The tree is right next to a playground. I wonder if a child ever asks: why is there a tree growing on another tree?