How big are they? I've never bothered to girdle a tree before I've introduced it to "my little friend" the chainsaw...but I suppose you could.
I usually wait until winter to launch my attacks...woodcutting in summer isn't much fun and the leaves are out of the way.

The norways are of various sizes from two inch diameter to a foot in diameter (there might even be some bigger ones but I don't have them positively identified yet). I rely on the help of others for actual chainsawing so I like to have alternative methods if they don't show up.

You don't need a chainsaw to stop a tree from growing.A year ago,last august,when I relised that there were scattered norway maples infiltrating the woods around my house,I sharpened a small hatchet and went about girdeling them all.Some were only a couple of inches in diameter but others were a foot thick and 60 feet tall.Its a lot of work to take down a tree that size and girdeling it will accomplishes the same thing with much less effort.The trees survived thru last fall,and leafed out normally in the spring.Only towards the end of this summer did I notice,by their withering canopy, that they were responding to the fatal wounds that I had inflicted.I don't expect them to leaf out again this coming spring.Having them decline slowly allowed the surrounding trees to respond to their fading shadow this summer and helped avoid a weedy response to the sudden change in light intensity on the forest floor that would have resulted from just cutting them down.I expect them to stand as dead snags for a few years,possible providing habitat,added shade, and/or firewood.In an afternoon with a small tool I was able to remove a couple dozen problem trees with as little disturbance as posible.

I agree with NYWoodsman - girdling Norway Maples is a good way to get rid of them. They will die in slow-motion, but you'll be left with lots of standing dead wood, which is great habitat for woodpeckers and many other birds that nest in used woodpecker holes. I'd girdle them all now, then if you want to cut some of them later you can.

If you girdle them this winter they will probably leaf out next spring and look reasonably healthy all summer. Toward the end of next summer you will want to check to verify that the bark hasn't grown over the wound. They will be completely dead in a couple of years.

Thanks. I was wondering about the best way to go.
Some that I girdled in the past took a long time to croak.
One that we cut down to about 4 feet high and girdled is rebounding like crazy. I guess I should re-girdle that one. As always, it appears that patience is required. If I leave snags I could drill holes in them for solitary native bees like I have been meaning to do.