Last week I walked on the South Downs and this week on the edge of the Chilterns. What they have in common is chalk grassland. This picture taken on the Downs shows the characteristic profile- deep chalk topped with a thin layer of lime-rich soil. Calcareous grassland is not rich in nutrients but conversely it is one of our richest habitats for flowering plants, insects, birds and mammals. The spongey turf is noted for sustaining as many as 45 species of flowering plant per square metre.