I see from your picture you have a FEL. Why not just push them out of the ground and pile them up??
On the other hand back when we were cleaning up our farm we would bushhog any thing the tractor would run over. We had an old beat up 5' mower we didn't care about though.
On the other hand back when we were cleaning up our farm we would bushhog any thing the tractor would run over. We had an old beat up 5' mower we didn't care about though.