Ancient chalk grassland is a very biodiverse habitat. It is often quoted as having 40-50 species of flowering plant per square metre of turf, which makes it the UK equivalent of the tropical rain forest!
In fact chalk grassland is actually rarer than tropical rain forest. According to the Sussex Biodiversity Action Plan
, there are only around 2,600 hectares of chalk grassland now surviving in Sussex and only around 3% of the South Downs is now chalk grassland.