4. As regards any semi-natural rough grazings which are the subject of an agreement and where heather forms at least 25 per cent but not more than 50 per cent of the vegetation cover—
(1) the farmer shall graze with cattle or sheep at an average annual stocking rate not exceeding 0.15 livestock units per hectare;
(2) the farmer shall, between 1st September in any year and 31st March in the following year, graze with cattle or sheep at an average annual stocking rate not exceeding 0.10 livestock units per hectare.