Saale valley. Its production is marketed as Saale-Unstrut wines. Forestry plays an important role in Thuringia because 32% of the Thuringian territory is forested. The most common trees are spruce, pine and beech. There are many wood and pulp-paper factories near the forested areas. Industry and mining Like most other regions of central and southern Germany, Thuringia has a significant industrial sector reaching back to the mid-19th-century industrialisation. The economic transition after the German reunification in 1990 led to the closure of most large-scale factories and companies, leaving small and medium-sized ones to dominate the manufacturing sector. Well-known industrial centres are Jena (a world centre for optical instruments with companies like Carl Zeiss, Schott and Jenoptik) and Eisenach, where BMW started its car production in the 1920s and an Opel factory is based today. The most important industrial branches today are engineering and metalworking, vehicle production and food industries. Especially the small and mid-sized towns in central and southwestern Thuringia (e.g. Arnstadt, Schmalkalden and Ohrdruf) are highly industrialised, whereas there are fewer industrial companies in the northern and eastern parts of the Land. Traditional industries like production of glass, porcelain and toys collapsed during the economic crises between 1930 and 1990. Mining was important in Thuringia since the later Middle Ages, especially within the mining towns of the Thuringian Forest such as Schmalkalden, Suhl and Ilmenau. Following the industrial revolution, the old iron, copper and silver mines declined because the competition from imported metal was too strong. On the other hand, the late 19th century brought new types of mines to Thuringia: the lignite surface mining around Meuselwitz near Altenburg in the east of the Land started in the 1870s, and two potash mining districts were established around 1900. These are the Südharzrevier in the north of the state, between Bischofferode in the west and Roßleben in the east with Sondershausen at its centre, and the Werrarevier on the Hessian border around Vacha and Bad Salzungen in the west. Together, they accounted for a significant part of the world's potash production in the mid-20th century. After the reunification, the Südharzrevier was abandoned, whereas K+S took over the mines in the Werrarevier. Between 1950 and 1990, uranium mining was also important to cover the Soviet Union's need for this metal. The centre was Ronneburg near Gera in eastern Thuringia and the operating company Wismut was under direct Soviet control. General economic