thumb|The machair on [[Berneray, North Uist|Berneray, Outer Hebrides]]
thumb|Machair east of [[Uig,_Lewis|Uig Bay, Lewis]]
thumb|The machair towards West beach, Isle of Berneray, Outer Hebrides
A machair (; sometimes machar in English) is a fertile low-lying grassy plain found on part of the northwestern coastlines of Ireland and Scotland, particularly the Outer Hebrides. The best examples are found on North and South Uist, Harris and Lewis. Machairs in Ireland are listed as priority habitats, receiving the highest level of protection, in the EU Habitats Directive.
Etymology
Machair is a Gaelic word meaning "fertile plain", but the word is now also used in scientific literature to describe the dune grasslands unique to western Scotland and northwest Ireland. It had been used by naturalists since 1926, but the term was not adopted by scientists until the 1940s. The word is used in a number of Irish, Scottish and Manx place names to refer to low-lying fertile ground or fields, even in areas not on duneland. although a number of systems still evade classification. 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. Changes in the Common Agricultural Policy, which decoupled production from subsidies, reduced the amount of grazing taking place in many crofting areas, and led to some areas being undergrazed or abandoned. A lack of native seed increases the need for fertiliser and herbicides. In January 1993, the storm which ran MV Braer aground off Shetland eroded of machair along the entire length of Uist and Barra.