Livestock shall be managed in such a way as to avoid overgrazing. Where the Scottish Ministers form the opinion that land was being overgrazed, a management regime including a maximum (and, where appropriate, a minimum) stocking rate to be observed on that site will be prescribed. Overgrazing is defined as grazing land with livestock in such numbers as to adversely affect the growth, quality or species composition of vegetation (other than vegetation normally grazed to destruction) on that land to a significant degree.