Ideally I would have talked to the neighbor before the project started but if for some reason that didn't happen, it probably depends on the neighbor and what cleaning them up off of the neighbors field is going to entail.   

Is it a quick in/out with a small loader tractor on dry/frozen ground to drag a few branches out or is it driving into a soft/wet newly established alfalfa field to get a 80' tall tree and root ball with a dozer or excavator that's gonna really tear stuff up?