The spruce-fir forest—also called the boreal or Canadian forest—is a relict of the ice ages, when mean annual temperatures in the Smokies were too cold to support a hardwood forest. While the rise in temperatures between 12,500 and 6,000 years ago allowed the hardwoods to return, the spruce-fir forest has managed to survive on the harsh mountain tops, typically above . About of the spruce-fir forest are old-growth.