Field Guide to Native Oak Species of Eastern North America(COLORED EDITION) Oaks are primarily temperate region trees and shrubs numbering approximately 600 species worldwide. Oaks have occupied the nonglaciated landscape of North America since the Cretaceous Period. Fifty oak species are represented in two thirds of the eastern North American forest cover types and dominate 68 percent of hardwood forests (191 million acres). Oaks have figured prominently in folklore, construction, food sources, medications,