The foregoing trees, shrubs and herbs are also more widely distributed in less rich mesic forests that generally occupy coves, stream valleys and flood plains throughout the southern and central Appalachians at low and intermediate elevations. In the northern Appalachians and at higher elevations of the central and southern Appalachians these diverse mesic forests give way to less diverse "northern hardwoods" with canopies dominated only by American beech, sugar maple, American basswood (Tilia americana) and yellow birch and with far fewer species of shrubs and herbs.

Where are the northern hardwoods the most diverse?