Here's an article on hedgerows in the UK.
I remember visiting North Carolina ASCS offices with the district director (this was 1968 or 9) and noticing some barbed wire fences (not many in the tobacco-growing area) with the wire on the outside of the posts. I was struck because in NY we put the wire on the inside; dad explained it meant that cows pushing against the wire were pushing against the post, while if it were on the outside they would be forcing the staple out of the wood.
Years later I learned the difference related to the way agriculture developed in the Northeast versus the South. In the Northeast livestock were fenced in; field crops were attractive to livestock. In the South livestock, especially hogs, were left to roam free, field crops of tobacco and cotton weren't attractive to livestock, fields of corn etc. that were attractive were protected by fencing out.
Now I'm guessing the use of hedgerows in the UK reflects the relative scarcity of wood--no split rail fences there, the fact that fields developed long before barbed wire became available, and the development of a historic pattern. Hedgerows would seem to require a long lead time to grow; not like a fence which can go up in a few days. So if farms have been around for centuries, there was time for hedgerows to develop.