The Cross Timbers is a complex mosaic of woodlands and grasslands that form a broad ecotone between the eastern deciduous forests and the grasslands of the southern Great Plains; covering about 26,000 square miles. East and West Cross Timbers couch the Fort Worth Prairie on the east and west. Although they both have sandy soil foundations, they are noticeably different.
The East Cross Timbers is a narrow strip of dense post oak/blackjack oak woods that follow I-35 between the Blackland Prairie to the east and the Fort Worth Prairie to the west. In pre-settlement times, it was so dense with underbrush that it was known as the ‘Cast Iron Forest’. It acted as a barrier between the settled eastern U.S. and the wild, untamed west. Occasional pockets of prairie emerge from the woods. This woodland has mostly disappeared due to urban development.
The West Cross Timbers is a less defined woodland mixed with savanna. In its eastern portion, the post oaks are grandiose and grow on Cretaceous sandy soils; in the western fringes the trees become stunted and grow on Pennsylvanian geologic-era sandstone ridges. Interspersed amongst the rocky woodlands and savannas are prairie glades. These glades are areas of clay soils that host plants that do not commonly grow in the surrounding sandy soils.
West Cross Timbers savanna featuring sandy soils