Not many ancient trees are left in Oklahoma. In the 1880s, sawmills were established in the forests of the eastern mountains. The sturdy and gnarly trees of the cross timbers were not considered commercially viable, but were used locally by settlers for fuel and building materials. The cross timbers is a transitional woodland, between the grasslands and the eastern deciduous forest. Trees on the open flats were first to fall to the ax and saw. As the cutting of trees in the cross timbers pushed back to steeper ridges and rockier hillsides, more trees were left uncut. On these less accessible, locations we now find the remnants of the ancient cross timbers forest.
The trees of the cross timbers are not the tall stately trees of our eastern forests, not the shrubby scrub of the western grasslands, but the cross timber trees fall in between – taller than a person, gnarlier than a pine, less showy than a maple in autumn. The cross timber trees have a character all their own. As described above, the cross timbers can be a dense forest of thick undergrowth and stout, low branches. Or it can be a more typical savanna with widely spaced trees and grassy expanses.
The tough, slow growing trees of the cross timbers vary across the ecoregion, but typical dominant species are post oak (Quercus stellata), blackjack oak (Q. marilandica), chinquapin oak (Q. muehlenbergii), hackberry (Celtis occidentalis), and pecan (Carya illinoinensis). The canopy (top of the tallest trees) is not high and can be quite a bit shorter when the woodland is on a dry ridge-top where the wind shears the tree limbs. The trees found in the shade of the tall canopy can be redbud (Cercis canadensis), persimmon (Diospyros virginiana), sumac (Rhus spp.), and eastern red cedar (Juniperus virginiana).