In the NE of Scotland they are called "roondies" but in Aberdeenshire in particular there is a reference to the devil , something like the "Deil's Share " , which has echoes of Bataille's "Accursed Share " . It is seen as wasted ground that can't and possibly shouldn't be ploughed , the trees can be old when oak or beech , Scot's Pine is also common and could provide a bit of shelter for livestock . Often natural mounds/moraines get the same treatment and it's only when dug that it's realised that they are not man made .