The area is distinctive for having tree species typically found further south, and reaching their northern limits. One example is pitch pine ("Pinus rigida"). Shallow soils and recurring fire have also produced unusual fire barren communities. These provide habitat for rare plants, such as bear oak ("Quercus ilicifolia") and deerberry ("Vaccinium stamineum"), as well as rare animals, such as the five-lined skink ("Plestiodon fasciatus") and gray rat snake ("Pantherophis spiloides"). There is high bird diversity, including the cerulean warbler, considered nationally endangered owing to the destruction of forests. Although the most important factor producing the fauna and flora is likely the bed rock, the moderating effect of the Great Lakes may also be factor. Also, some northern species extend their range south, drawn by the rugged granite landscapes of the Canadian Shield.