How has hill farming shaped the environment over hundreds of years?

Originally much of our country was covered in trees and other vegetation. Large areas of trees were cleared as towns and cities developed. The landscape was changed. In the countryside farming has shaped the landscape. All of us now think of the countryside as well kept fields filled with sheep and cows or with crops. We think of farms, barns, dry stone walls and country lanes. This is very different from how it used to be. If our farms close the countryside would become overgrown as vegetation was allowed to grow unchecked.