Those are cool.
They have some harvester heads called hot saws, they grab a tree up to 2' in diameter and a great big wheel with huge teeth slices it off at the ground then you set it where you want it. The chunks of wood that it spits out are as big as a baseball and can fly about 50 yards. They really hurt!!!!!!
This is what we see almost daily in north Louisiana. We have a lot of pine tree farms and these are amazing to watch. Cuts, de-limbs (debarks), cuts to length and stacks. Guys can cut about 150 trees per hour.