Regarding George Monbiot’s article (There’s an invader turning huge swathes of Britain into deserts – and these dead zones are spreading, 9 June), yes, molinia (purple moor-grass) is a serious scourge of many of the UK’s acidic upland landscapes. In 1999, while still residing in my home county of East Sussex, I began a conservation grazing initiative using Exmoor ponies to combat the growing threat to the South Downs’ chalk grasslands from a very similar grass, Brachypodium (tor grass), which back then I estimated was affecting well in excess of 200 hectares. This grass is of little use to farmers and also seriously depletes biodiversity.