Texas Hill Country Oak Savanna

This upland system occurs primarily on soils derived from chalk or limestone of Cretaceous or Pennsylvanian origin in the Edwards Plateau; it forms the matrix within this ecoregion. It can also occur on limestone in the shortgrass regions of Texas and north into Oklahoma in areas such as the Arbuckle Mountains. This system is typified by a mosaic of evergreen oak forests, woodlands and savannas over shallow soils of rolling uplands and upper slopes within the Edwards Plateau and Lampasas Cutplain. Quercus fusiformis or Juniperus ashei typically dominate the canopy of this system. Other species may include Quercus buckleyi, Quercus laceyi, Quercus stellata, Ulmus crassifolia, Fraxinus albicans, Quercus sinuata, Quercus vaseyana, Sophora secundiflora, Mahonia trifoliolata, and Diospyros texana. Physiographic expression of this system varies from dense mottes (patches of forest where canopy cover approaches 100%) interspersed with grasslands to open savannalike woodlands with scattered individual or small groups of trees. Understories can contain various shrubs and graminoids, including Cercis canadensis var. texensis, Forestiera pubescens, Sideroxylon lanuginosum, Diospyros texana, Rhus trilobata, Bouteloua spp., Schizachyrium scoparium, Nassella leucotricha, Carex planostachys, Aristida purpurea, Aristida oligantha, Liatris punctata var. mucronata, Stillingia texana, Symphyotrichum ericoides, Stenaria nigricans, Monarda citriodora, and Salvia texana. Grasslands dominated by Schizachyrium scoparium occur in small patches within more closed woodlands and in larger patches between mottes or in open savannalike woodlands with scattered trees. Grasslands in this system tend to grade from shortgrass communities in the west to mixedgrass communities to the east. Substrate (limestone) determines the range of this system within given examples. Some disturbed areas of the western plateau are now dominated by mesquite woodland. Natural mesquite woodlands are believed to have occurred on the deeper soils of adjacent riparian systems.

This forest and woodland system is dominated by species such as Quercus fusiformis, Quercus laceyi, Quercus vaseyana, Juniperus ashei, or Pinus remota. Other species may include Quercus buckleyi, Ulmus crassifolia, Fraxinus albicans (= Fraxinus texensis), Quercus sinuata, and Diospyros texana. Certain uplands may have mottes of Quercus fusiformis dominating a savannalike woodland. Physiographic expression varies from dense mottes (patches of forest where canopy cover approaches 100%) interspersed with large or small grassland patches to open savannalike woodlands with scattered individual or small groups of trees. Understories can contain various shrubs and graminoids, including Cercis canadensis var. texensis, Forestiera pubescens, Sideroxylon lanuginosum, Diospyros texana, Rhus trilobata, Mahonia trifoliolata, Sophora secundiflora, Opuntia engelmannii var. lindheimeri, and Cylindropuntia leptocaulis. Grasses and forbs include Bouteloua spp., Schizachyrium scoparium, Sorghastrum nutans, Bouteloua curtipendula, Bothriochloa barbinodis, Bothriochloa laguroides ssp. torreyana, Nassella leucotricha, Hilaria belangeri, Bouteloua dactyloides, Andropogon gerardii, Bouteloua hirsuta, Bouteloua rigidiseta, Muhlenbergia reverchonii, Muhlenbergia lindheimeri, Carex planostachys, Aristida purpurea, Aristida oligantha, Liatris punctata var. mucronata (= Liatris mucronata), Stillingia texana, Symphyotrichum ericoides, Stenaria nigricans (= Hedyotis nigricans), Monarda citriodora, and Salvia texana. Grasslands dominated by Schizachyrium scoparium occur in small patches within more closed woodlands and in larger patches between mottes or in open savannalike woodlands with scattered trees. Grasslands in this system tend to grade from shortgrass communities in the west to mixedgrass communities to the east. Substrate (limestone) determines the range of this system within given examples. The herbaceous stratum is often dominated by non-native grass species, especially Bothriochloa ischaemum var. songarica.

This system is primarily found on Cretaceous limestones of the Edwards Plateau and Limestone (also referred to as Lampasas) Cutplain, but also associated with Pennsylvanian limestones of the Palo Pinto Formation and Winchell, Ranger, Home Creek limestone in the vicinity of Palo Pinto County, as well as on Cretaceous chalk formations in the northern Blackland Prairie and Cretaceous limestones of the western Crosstimbers and Rolling Plains. It ranges north into Oklahoma and is found on rolling to level upland topography, often on plateau tops, but also on gentle slopes. Soils are generally loams, clay loams, or clays, often with limestone parent material apparent. Low Stony Hill, Adobe, Clay Loam, and Shallow Ecological Sites are commonly associated with this system (Elliott 2011). Soil moisture and topography influence this system.

Substrate (limestone) and topographic position primarily influence this system. Fire, grazing and browsing may also influence this system.

This system is found primarily within the Edwards Plateau ecoregion but can extend north into Oklahoma and into portions of the Southern Shortgrass region of Texas.