<P> The Great Smokies are part of an International Biosphere Reserve . The range is home to an estimated 187,000 acres (76,000 ha) of old growth forest, constituting the largest such stand east of the Mississippi River . The cove hardwood forests in the range's lower elevations are among the most diverse ecosystems in North America, and the Southern Appalachian spruce - fir forest that coats the range's upper elevations is the largest of its kind . The Great Smokies are also home to the densest black bear population in the Eastern United States and the most diverse salamander population outside of the tropics . </P> <P> Along with the Biosphere reserve, the Great Smokies have been designated a UNESCO World Heritage Site . The U.S. National Park Service preserves and maintains 78 structures within the national park that were once part of the numerous small Appalachian communities scattered throughout the range's river valleys and coves . The park contains five historic districts and nine individual listings on the National Register of Historic Places . </P> <P> The name "Smoky" comes from the natural fog that often hangs over the range and presents as large smoke plumes from a distance . This fog is caused by the vegetation exhaling volatile organic compounds, chemicals that have a high vapor pressure and easily form vapors at normal temperature and pressure . </P> <P> As a result of the 2016 Great Smoky Mountains wildfires, the Great Smoky Mountains have received international media coverage . </P>

Why do they call it the smoky mountains