Machair differs from the
links on the east coast of Scotland in having a lower mineral content, whereas the links are high in
silica. Machair plains are highly
calcareous, with
calcium carbonate concentrations ranging from 20% to 80% on the beaches, and decreasing further away from the coast.
Formation The modern theory of machair formation was first put forward by
William MacGillivray in 1830. He worked out that shell fragments are rolled by waves towards the shore, where they are further broken up. The small shell fragments are blown up the beach to form mounds, which are then blown inland.
Humans Human activity has played an important role in the creation of the machair. Archaeological evidence suggests that some trees were cleared for agriculture as early as 6000 BC, but there was still some woodland on the coast of
South Uist as late as 1549. Seaweed deposited by early farmers provided a protective cover and added nutrients to the soil. The grass is kept short by
cattle and
sheep, which also trample and add texture to the
sward, forming tussocks that favour a number of bird species. The
soil is low in a number of key
nutrients, including trace elements such as
copper,
cobalt and
manganese, requiring cattle to be fed supplements or taken to summer pastures elsewhere. The sandy soil does not hold nutrients well, making artificial fertilisers ineffective and limiting the crops that can be grown to certain varieties of
oats and
rye, and
bere barley. ==Ecology==