Rent a tractor and bush hog. You will have it cleared in a couple hours instead of days and will not have a sore back.
... a Swedish Axe, the thin bladed unit with a metal bow holding the blade. You can move a lot of material in a day, with those, and it won't leave your ears ringing!
I've been looking into this a bit because I have an area of tag alders I would like to kill. You can cut them but the roots remain and suckers will inevitably come back up making things worse. You can cut it all again every other year but it seems that the thing to do is spray those fresh stumps with an herbicide that works on that species, e.g. Garlon, on the same day you cut them. Or a mixture of herbicides for a broader range of trees. Google slash and squirt.
edit: It seems, though, that a person needs a pesticide operator's licence to purchase and use that class of herbicide in Canada. Can anyone confirm this, or are there other solutions?
Here is my setup for brush mulching, trail clearing, fire brakes, land reclaimation, ROW Clearing.
Excuse the slow careful work, I was just learning at the time, and being careful as the ballistic door had not yet arrived.
I'm planning on renting a similar rig in the spring to clear some stuff. Do you do commercial work?