Hi Paulneill, i see it and don't believe it

the risk here is the sap cant flow up or down the trunk or will be severely reduced because of the cut in the outer trunk and plastic . Way back when things were done differently ring barking trees with an axe by cutting into the outer sap wood all the way around the tree was the way to kill them off .Just removing the bark wouldn't kill the tree , but cutting into the last couple of years growth / outer sap wood , would stop them dead in there tracks .
I think a double wire tourniquet would do the job with a couple of nicks in the base to stop the wire from slipping upwards ,even burying the trunk will produce roots while the old roots are in tack especially on a Trident Maple . Alternatively when the top was chop , i dare say in winter , slice the old root base off and use all of the available flare in the base . Tridents can be severed almost anywhere close to the base and planted out in winter for a complete regrowth of the roots by mid summer .
Good luck with this one .Cheers Alpine