Common (Translated Scientific) Name: Post Oak - Blackjack Oak Forest & Woodland Group

Colloquial Name: Cross Timbers & East-Central Texas Plains Oak Forest & Woodland

Hierarchy Level:  Group

Type Concept: This group consists of short, stunted woodlands and forests in eastern, central and western Oklahoma, ranging north to southeastern Kansas, and south through central Texas to the Inner Coastal Plain. The physiognomy of this vegetation varies from open woodlands with scattered trees to dense forests with a dense and viney understory. Canopy height is short (<15 m). This vegetation is located where the forests of the eastern U.S. transition into grasslands of the central U.S. Patches of forests and woodlands are often interspersed with patches of tall- and midgrass prairie. The area consists of irregular plains and rugged scarps with primarily sandy to loamy soils that range from shallow to moderately deep. Rainfall can be moderate, but somewhat erratic, therefore moisture is often limiting during part of the growing season. Short, stunted Quercus stellata and/or Quercus marilandica characterize and dominate this group. Another common canopy tree is Carya texana. Other component species may include Carya cordiformis, Celtis laevigata var. reticulata, Quercus prinoides, Ulmus crassifolia, Ulmus alata, Quercus fusiformis, Quercus incana, and Quercus virginiana within their respective ranges. The understory often contains species typical of the surrounding prairies, in particular Schizachyrium scoparium. Small trees or shrubs such as Sideroxylon lanuginosum, Juniperus spp., Smilax spp., and Rhus spp. may also be present. There is considerable variation in associated species in a broad transition from coastal plain to interior areas, and correspondingly from east to west. Drought, grazing, and fire are the primary natural processes that affect this group. With the disruption of these processes today, many examples of this vegetation trend more toward dense stunted forest than open woodland. Overgrazing and conversion to agriculture, along with fire suppression, have led to the invasion of some areas by problematic brush species such as Juniperus virginiana and Juniperus ashei and Prosopis glandulosa farther south in Texas and Oklahoma. It has also led to decreases in native grass cover allowing for annual grasses and forbs to invade.

Diagnostic Characteristics: Tree canopy strongly dominated by Quercus stellata and/or Quercus marilandica (>90% cover). Other associates may be Carya texana, Carya cordiformis, Celtis laevigata var. reticulata, Quercus prinoides, Ulmus crassifolia, Ulmus alata, Quercus fusiformis, Quercus incana, and Quercus virginiana, but lacking many eastern forest or shrub associates such as Quercus falcata, Quercus alba, Quercus coccinea, Pinus echinata, Vaccinium pallidum, Vaccinium stamineum, and Gaylussacia spp. This group only occurs in Kansas, Oklahoma and Texas.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This group is currently circumscribed at the group level, separate from somewhat similar vegetation occurring farther east, that is also characterized by Quercus stellata and Quercus marilandica. It is differentiated from these forests by the lack of other "dry-site" eastern oaks, pines, and shrubs, such as Quercus falcata, Quercus alba, Quercus coccinea, Pinus echinata, Vaccinium pallidum, Vaccinium stamineum, Gaylussacia spp., among others. Even those forests and woodlands in the nearby Ouachita and Ozark mountains, though characterized by post oak and blackjack oak, have a flora more strongly associated with eastern forests. This group represents the western edge of the eastern deciduous forests, and as such is lacking many of the eastern woody species. In addition, it represents a transition of forests to grasslands, and some evidence suggests this group once had a higher grass cover, linking it more closely with the Great Plains grasslands. Many factors are thought to have contributed to this increase in woody cover, primarily the imbalance in two main natural processes that helped maintain this grassland state: fire and grazing. Because this vegetation is allied with the grasslands and was perhaps more so under natural conditions, and because many of the eastern species present in similar vegetation farther east are absent in this vegetation, it is currently circumscribed at the group level. Further investigation and review are necessary to determine if this is appropriate. Three or more alliances are expected to be needed, one north of the range of Ulmus crassifolia and one south, that also brings in some southeastern components such as Ulmus alata, Ilex vomitoria, Callicarpa americana, and Vaccinium arboreum, and then, perhaps one west of the range of these eastern shrubs and where western shrubs such as Mahonia trifoliolata, Condalia hookeri, Colubrina texensis, among others are more prominent. An alliance reflecting a mixture of Quercus stellata and Quercus virginiana may also be warranted in the southern limit of this vegetation.

Similar NVC Types: No Data Available

note: No Data Available