The Southern Appalachian region is one of the biologically richest in the temperate zones. Species diversity is especially high among plants, insects, fungi, and amphibians (including the world’s highest concentration of salamanders).
One reason for such high biodiversity is abundant rainfall. Another reason is that when the glaciers pushed southward in the last ice ages, they forced many northern species southward, then when glaciers retreated, many of those northern species sought the cooler temperatures of higher elevations, and stayed. As a result, the region has a mix of southern species in low elevations and northern species at high elevations.
(Photo of Red Eft by Tracy Hicks.)