The world heritage committee says that the addition comes "in recognition of the testimony that the forest provides to the exceptional development and impact on the beech eco system in Europe during the last ice age".
The Sonian Forest, in and outside Brussels, joins beech forests in Ukraine, Slovakia and Germany. Forests in Albania, Bulgaria, Italy, Croatia, Austria, Romania, Slovenia and Spain have now also been added.
Belgium's three regions backed the addition. The Sonian Forest is the only Belgian forest that occurs in all three regions.
Flemish PM Geert Bourgeois noted how unique the addition of the forest was: "Until now all world heritage in Belgium has been man-made and labelled 'cultural' world heritage. The Sonian forest is the first "natural" world heritage."