what about an old hay baler?
most common here are PTO driven, but you can get em' with their own motor...probably better...park it and use the tractor for something else.
plus, I think our old JD baler (with motor) had a belt driving the flywheel, and a tension lever/pulley to engage/disengage...could easily kick it out if it jammed
add a chute/slide in the front for feeding and protection from the tines
probably feed it only fresher green stuff, and you'd have to do some pre-processing to avoid hassles, but...
in the end it should crap out bales of kindling
then add either a young feller' or a conveyor/elevator at the back to dump em' into a trailer/truck/pile
won't dry as fast all baled up, but that can be overcome
and, won't be 100% uniform length, but I think you could live with it
bales would be convenient to handle and transport...
I dunno...with that flywheel and huge knife it should work