valuable timber. Oak bark is also rich in tannin, and is used by tanners for tanning leather. Oak galls were used for centuries as a main ingredient in iron gall ink for manuscripts, harvested at a specific time of year. In Korea, oak bark is used to make shingles for traditional roof construction. Culinary Barrels for aging wines, sherry, and spirits such as brandy, Irish whiskey, Scotch whisky and Bourbon whiskey, are made from European and American oak, with single barrel whiskey fetching a premium. The use of oak in wine can add gustatory dimensions depending on the type of oak. Oak barrels, which may be charred before use, contribute to the colour, taste, and aroma of their potable contents, imparting a desirable oaky vanillin flavour. A dilemma for wine producers is to choose between French and American oakwoods. French oaks (Quercus robur, Q. petraea) give greater refinement, and are chosen for the best, most expensive wines; while American oak contributes greater texture and resistance to ageing, but produces a more powerful bouquet. Oak wood chips are also used for smoking fish, meat, cheeses, and other foods. The bark of the cork oak is used to produce wine stoppers (corks). This species grows around the Mediterranean Sea, with Portugal, Spain, Algeria, and Morocco producing most of the world's supply. The bark of the white oak is dried and used in medical preparations. Acorns are used for making flour or roasted for acorn coffee. Conservation According to a comprehensive report by The Morton Arboretum and the International Union for Conservation of Nature (IUCN) an estimated 31% of the world's estimated 430 oak species are threatened with extinction, while the study found an estimated 41% of oak species to be of conservation concern. The countries with the highest numbers of threatened oak species according to the report are China with 36 species, Mexico with 32 species, Vietnam with 20 species and the USA with 16 species. While the cause of decline is still partly unknown for some species, the main causes the scientists determined were climate change and invasive pests in the US, and deforestation and urbanization in Asia. In the Himalayan region of India, oak forests are being invaded by pine forests due to the increase in temperature. The associated species of pine forest may cross frontiers and become new elements of the oak forests. In eastern North America, rare species