A hedge or hedgerow is a close-knit row of shrubs and sometimes tree species. They were usually planted and "trained" to form a barrier. They marked the boundary of an area, and so were a sign of possession.
Livestock farmers use them to prevent cattle straying out of fields. Animals which cannot usually be contained in fields (hill sheep for example) need a man and dog to look after them, which is an expense. Hedges were much more common before modern agriculture. Modern crop farming uses machines to gather the crop, and so hedges have almost disappeared in some areas.