Natural History

Oklahoma – A Botanical Crossroads

Biologically, Oklahoma is quite a remarkable state! It lies at the intersections of some of the most significant ecosystems of North America.  The tallgrass prairie of the continent’s center gives way to the shortgrass prairie of the west, the mesquite grassland of the southwest, and the deciduous forest of the east.

Within the state’s borders, one can encounter ponderosa pine and other Rocky Mountain species at the end of the Panhandle; species characteristic of New England forests in the northeastern corner; stately bald cypress trees and other Gulf Coast species in the swamps of the extreme southeastern corner; and cacti and other species characteristic of the continent’s southwestern deserts in the southwestern corner.

Within Oklahoma are found approximately 175 families, more than 850 genera, and about 2,600 species of vascular plants.   This diversity of plants and vegetation types is related to the state’s tremendous ecogeographic diversity — variation in precipitation, temperature, geology, topography, and soils. From grasses to trees to cacti, Oklahoma has them all!    

The Cross Timbers

Nowhere is the intersection among these different ecosystems more evident than in the Cross Timbers, a distinctive vegetation type that extends from southeastern Kansas across Oklahoma to north-central Texas. The Tulsa Botanic Garden is situated in the midst of this remarkable ecosystem.

In the Cross Timbers, the tall trees of the continent’s eastern deciduous forests do battle with the grasses of the central prairies, and thus form a mosaic of upland forests, tallgrass prairies, savannahs, and glades. Although the Cross Timbers forests contain many of the same species as found in the forests farther east, here the trees are reduced in stature, often stunted and gnarled. 

In places these Cross Timbers forests are so dense, that many early travelers considered them impenetrable. In 1835 Washington Irving and Charles Latrobe described traveling through them as "struggling through forests of cast iron," and it is reported that early wagon trains traveled to the north or south to avoid crossing them.

Fortunately, these distinctive features of the Cross Timbers that so vexed early travelers have left Oklahoma with one of its greatest botanical treasures.  The Cross Timbers is one of the least disturbed forest types in the eastern United States because its trees were too stunted to be worth logging, its terrain too steep to be farmed, and its soil too thin and rocky to grow crops. Large tracts are essentially intact, and thus appear much the same and contain many of the same animals and plants as they did prior to the arrival of Europeans.

As you walk the nature trail of the botanic garden and pass among the trees of the post oak—blackjack oak forest and the grasses and forbs of the tallgrass prairie, think of the many travelers before you who likewise passed through this remarkable ecosystem.  

Written by Ronald J. Tyrl, Ph.D and Jay B. Walker, Ph.D.