European Union representation within those institutions, a practice often referred to as "pooling of sovereignty". To become a member, a country must meet the Copenhagen criteria, defined at the 1993 meeting of the European Council in Copenhagen. These require a stable democracy that respects human rights and the rule of law; a functioning market economy; and the acceptance of the obligations of membership, including EU law. Evaluation of a country's fulfilment of the criteria is the responsibility of the European Council. No member state has yet left the Union, although Greenland (an autonomous province of Denmark) withdrew in 1985. Article 50 of
Greenland from Europe. There are no native or free-living reptiles or amphibians on the island. Phytogeographically, Greenland belongs to the Arctic province of the Circumboreal Region within the Boreal Kingdom. The island is sparsely populated in vegetation; plant life consists mainly of grassland and small bushes, which is regularly grazed by livestock. The most common tree native to Greenland is the European white birch ("Betula pubescens") along with gray-leaf willow ("Salix glauca"), rowans ("Sorbus aucuparia"), common junipers ("Juniperus communis") and other smaller trees, mainly willows. Greenland's flora comprises about 500 species of higher plants, i.e. flowering plants, ferns, horsetails and lycopodiophyta.