I can't say for sure but I believe it MAY be to do with scrub clearance; I know that the Hill Wardens hired an impressive piece of kit which was a large mechanical flail (i.e. spinning chains on a drum, suspended on a tractor) which was a "bit of a monster" and had the ability to whizz all the scrub (bracken, brambles and even medium-sized trees!) into pulp; the machine was used to great effect on Burrington Ham. It is possible, but without checking I can't say for sure, that the three lines on the picture are where such a machine has been trialled.