Texas Central Mineral Region Forest and Glade

This upland matrix system occurs primarily on coarse soils derived from the weathering of underlying Precambrian granites in the Llano Uplift region of Texas. The underlying intrusive granitic bedrock substrate determines the range of this system. It is composed of a mosaic of vegetation types, including closed-canopy forests, open woodlands, savannas and sparsely vegetated rock outcrops. Common trees include Quercus marilandica, Quercus fusiformis, Quercus stellata, Carya texana, Ulmus crassifolia, and Prosopis glandulosa. Subcanopy species may include Diospyros texana, Aloysia gratissima, Ungnadia speciosa, Ziziphus obtusifolia var. obtusifolia, Eysenhardtia texana, Aesculus glabra var. arguta, Opuntia engelmannii var. lindheimeri, Yucca elata, Nolina texana, and Cylindropuntia leptocaulis. Grasslands may be dominated by Schizachyrium scoparium, Sorghastrum nutans, Panicum virgatum, Bouteloua hirsuta, Bouteloua curtipendula, Nassella leucotricha, Bothriochloa laguroides, and Plantago wrightiana. Granitic glades and barrens are sparsely vegetated by crustose and foliose lichens, several ferns and fern allies, and cacti. This system also includes small (up to 16 m in diameter) shallow depressions that hold rainwater and support wetland flora including the Texas endemic, Isoetes lithophila.

This system is typified by a mosaic of vegetation types, including mixed oak forests and savannas over coarse soils and sparsely vegetated areas on rock outcrops. Species such as Quercus marilandica, Quercus fusiformis, Quercus stellata, Carya texana, Ulmus crassifolia, and Prosopis glandulosa may dominate the canopy of this system. Some areas are characterized by dense forest patches (mottes) of Quercus fusiformis, with various mixtures of other oaks and shrubs surrounded by open grasslands. Subcanopy species may include Diospyros texana, Aloysia gratissima, Ungnadia speciosa, Ziziphus obtusifolia var. obtusifolia, Eysenhardtia texana, Aesculus glabra var. arguta, Opuntia engelmannii var. lindheimeri (= Opuntia lindheimeri), Yucca elata, Nolina texana, and Cylindropuntia leptocaulis (= Opuntia leptocaulis). The ground flora may contain Schizachyrium scoparium, Sorghastrum nutans, Panicum virgatum, Bouteloua hirsuta, Bouteloua curtipendula, Nassella leucotricha, Eragrostis intermedia, Croton monanthogynus, and Plantago wrightiana. In addition to oak woodlands and grasslands, this system also includes granitic glades and barrens. These are sparsely vegetated areas characterized by crustose and foliose lichens, several ferns and fern allies, and cacti, including Cheilanthes lindheimeri, Pellaea ternifolia, Selaginella arenicola ssp. riddellii, Selaginella peruviana, Selaginella wrightii, Echinocereus reichenbachii, and Echinocereus coccineus. Other species that may occur in cracks and crevices or slight depressions with shallow, gravelly soil include Eriogonum tenellum, Lechea san-sabeana, Sedum nuttallianum, Tripogon spicatus, Plantago wrightiana, Phemeranthus parviflorus (= Talinum parviflorum), Helenium amarum, Campanula reverchonii, Aphanostephus skirrhobasis, and Hypericum gentianoides. Small-scale shallow vernal pools formed within barrens by weathering of the granitic surface support Crassula aquatica, Sedum nuttallianum, Phemeranthus parviflorus, Eleocharis montevidensis, Elatine brachysperma, Juncus diffusissimus, Allium canadense, Nothoscordum bivalve, Cooperia drummondii, Lepuropetalon spathulatum, Isoetes melanopoda, and the Texas endemic Isoetes lithophila. Larger pools often exhibit a pattern of zonation of the vegetation as soil accumulates in the center. Crevices in the rock outcrops tend to support scattered, stunted individuals of trees and shrubs found in the adjacent woodland. Endemics or near-endemics occurring within this ecological system include Isoetes lithophila, Campanula reverchonii, Eriogonum tenellum var. ramosissimum, Elatine brachysperma, Valerianella texana, Packera texensis, Tradescantia pedicellata, Brazoria enquistii, Indigofera miniata (= var. texana), and Tripogon spicatus.

This system is restricted to the Llano Uplift, also known as the central mineral region of Texas. Though named as an uplift because it is an intrusion of Precambrian metamorphic rocks and large granitic massifs, this area is generally lower in elevation than the surrounding Edwards Plateau (Walters and Wyatt 1982, Riskind and Diamond 1988). At a regional scale, it is a topographic bowl, though rock outcrops such as Enchanted Rock often produce dramatic increases in elevation at a local scale. Aside from these massif intrusions, topography is generally level to rolling. The substrate of granites, gneisses and schists determines the range of this system in central Texas. Elevation ranges from 251 to 686 m above sea level (825-2250 feet). Rainfall averages about 76 cm (30 inches), peaking in May or June and September. The central mineral region occupies approximately 1.5 million hectares in central Texas (Riskind and Diamond 1988). Mineralogy of the granitic material varies, with hornblende schist, graphite schist, quartz-feldspar gneiss and quartz-plagioclase-microcline rock common (Riskind and Diamond 1988). Soils are generally sandy loams, with gravelly soils common. They are generally acidic and coarse, resulting from weathering of the underlying granite. Many areas of exposed bedrock are present. Most frequently encountered Ecological Sites include Shallow Granite, Sandy Loam, Red Savannah, Gravelly Sandy Loam, Shallow Ridge, Granite Gravel, Sandstone Hill, and Granite Hill (Elliott 2011).

This ecological system is a complex of vegetation types. The different physiognomies are maintained by an interaction between site conditions and disturbance dynamics. The forest patches, woodlands, savannas and grasslands are thought to have been maintained historically by various fire frequencies and intensities. In the absence of natural or prescribed fire, increased cover of woody vegetation has increased in some occurrences. Native grazing may have also played a role in preventing woody encroachment though the rough terrain of much of this system would have limited the extent of native grazers.

This system is restricted to the Llano Uplift region of Texas.