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Calcareous grassland (or alkaline grassland) is an ecosystem associated with thin basic soil, such as that on chalk and limestone downland. Chalk Grassland HAP
, Medway on the North Downs. In June, these meadows are covered with chalk grassland flowers.]]There are large areas of calcareous grassland in northwestern Europe, particularly areas of southern England, such as Salisbury Plain and the North Downs and South Downs.
The machair forms a different kind of calcareous grassland, where fertile low-lying plains are formed on ground that is calcium due to shell sand (pulverised ).
The lichen flora of chalk grasslands represents an often overlooked component of calcareous grassland biodiversity. A comprehensive survey of English chalk grasslands in the 1990s identified two main lichen communities: the widespread Lecideetum watsomiae association found on chalk pebbles and flints, and the more restricted Fulgensietum fulgentis community. These lichen communities require specific conditions to grow, including areas of open ground created through natural or human disturbance, such as rabbit grazing, trampling, or historical agricultural practices. The richest lichen sites are often found where soil has been disturbed within the past century or where natural factors like create suitable habitats. Key factors promoting lichen diversity include the presence of stable , areas of nutrient-poor soil, and the presence of a small loess (windblown silt) fraction in the soil. Characteristic species include Gyalolechia fulgens and various Cladonia species. Many calcareous grassland lichen communities have shown significant decline since the mid-20th century, attributed to factors such as reduced grazing, nitrogen deposition, and habitat loss.
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