Ouch,
Frank it hurt reading that. Hope your recovering well. I to have been hit but not quite the same way. Luckily mine was from 260 yds and it had bounced and hit my shoulder (I know doesn't even count
). As far as your question goes, I have found that a lot of new courses that have been built on big open plots of land that did not have many mature trees on have had to try and plant trees. This is all very well, but the trees are often not very big and as has proven with your encounter do not provide much separation of holes. I am interested to know is this a relatively new course? Also 20 yards is quite a close distance to have a green and tee, normally they would have signs or the like warning against stray balls.
All the best and get well soon.