There are big machines that do this. They grab the tree in two places, and the machine saws thru the trunk and they pull the tree off to the side. I think that's what is happening here, but the machines are in the back behind the road - they are probably clearing them because they want them away from the road and wires.

I live in the PNW and we are always having trees removed. If they are on the roadside it is men with chainsaws, if it is a little farther back it is the big equipment - they clear entire mountain sides too.

Looks freaky unless you can see the machines ;)