The term calaminarian grassland is used for the distinctive plant communities associated with heavy metal mining, particularly the sparse vegetation of lead mine spoil and smelt mill waste where only metal-tolerant plants (known as metallophytes) can grow. The lead and other heavy metals are toxic to plants, the soils are nutrient poor, and the ground is often very dry in summer. The only plants that can grow here are small and slow-growing, and specially adapted to these stressful conditions.
The most easily recognised form of calaminarian grassland in the Yorkshire Dales is a short, open turf with exposed stones and areas of bare ground close to historic lead mining sites. The most common plants are sheep’s fescue and spring sandwort, which was used by miners as an indicator of a lead vein beneath the surface. Thyme, ribwort plantain, and thrift often grow with them. The bare ground between them supports a rich variety of lichens and mosses, and these are an important part of the plant community. Some of the lichens, such as Sarcosagium campestre and species of Vezdaea, are tiny and can only be seen with a hand lens, but they are quite beautiful and well worth the effort! There may be a living crust of cyanobacteria and other micro-organisms over the soil surface.
More grassy areas, where bent grass and harebell are more common, may have populations of alpine penny-cress. This plant is only found on heavy-metal contaminated sites in Britain, and accumulates astonishing levels of zinc in the shoot which deters grazing animals. Mountain pansy does well on less-contaminated ground.
Wetter ground also has some distinctive species, including Pyrenean scurvy-grass and the large green lichen Peltigera leucophlebia.
Even where there is an old lead mine or smelt mill the area of calaminarian grassland is often very small. Small patches on stony ground are being encroached on by scrub and coarse grasses from the surrounding area, so some grazing is needed to control this, preferably by rabbits or sheep. As they become smaller and more isolated from each other they are becoming more vulnerable to disturbance and many are gradually losing their species of interest. Even small areas need protecting.