Edwards Plateau Floodplain Terrace

Geology

This system usually occupies Quaternary alluvial deposits often within drainages largely underlain by Cretaceous limestones or drainages that receive outwash from landscapes dominated by these limestones.

Landform

Valley floors of large rivers and perennial streams. This system tends to occupy broad valley bottoms with alluvial deposits on the Edwards Plateau, and rivers and large creeks where outwash from the Edwards Plateau influences the substrate.

Soils

Bottomland soils of various types (Loamy, Clayey, and Sandy).

Parent Description

These are forests and woodlands with a canopy dominated or co-dominated by Carya illinoinensis (pecan), Ulmus crassifolia (cedar elm), Ulmus americana (American elm), Celtis laevigata (sugar hackberry), Celtis laevigata var. reticulata (netleaf hackberry), and/or Quercus fusiformis (plateau live oak). Carya illinoinensis (pecan) may be more likely to occur in deeper and better-developed alluvial soils. Apparent dominance of Carya illinoinensis (pecan) may also be an artifact of preferential harvesting of other species, leaving this species in greater abundance. Melia azedarach (chinaberry) is a common non-native tree encountered on floodplains. Other species present may include Fraxinus texensis (Texas ash), Fraxinus pennsylvanica (green ash), Juglans major (Arizona walnut), Quercus macrocarpa (bur oak), Quercus buckleyi (Texas oak), Acer negundo (boxelder), Sapindus saponaria var. drummondii (western soapberry), Juniperus ashei (Ashe juniper), Prosopis glandulosa (mesquite), and Platanus occidentalis (American sycamore). Quercus stellata (post oak) may be dominant on sandy soils within the floodplain at some sites. Woody species in the subcanopy may include Sideroxylon lanuginosum (gum bumelia), Ptelea trifoliata (wafer-ash), Cornus drummondii (roughleaf dogwood), Morus rubra (red mulberry), Diospyros texana (Texas persimmon), Parthenocissus quinquefolia (Virginia creeper), Vitis spp. (grape), Smilax bona-nox (greenbrier), Baccharis neglecta (roosevelt-weed), Malvaviscus arboreus var. drummondii (Turk's cap), Juniperus ashei (Ashe juniper), and Ilex decidua (possumhaw). The herbaceous layer may be continuous, though relatively sparse, or patchy with species such as Elymus virginicus (Virginia wildrye), Chasmanthium latifolium (creekoats), Nassella leucotricha (Texas wintergrass), Verbesina virginica (frostweed), and Carex spp. (caric sedge). Some sites lack, or have very sparse, overstory canopies and represent shrublands or grasslands. Shrublands may be dominated by species in the shrub layer of the surrounding woodlands. Other components or dominants may include species such as Prosopis glandulosa (mesquite), Acacia farnesiana (huisache), Sapindus saponaria var. drummondii (western soapberry), Juglans microcarpa (little walnut), Mahonia trifoliolata (agarito), and Cephalanthus occidentalis (common buttonbush). Grassland sites are frequently dominated by the non-native species Cynodon dactylon (bermudagrass) and/or Bothriochloa ischaemum var. songarica (King Ranch bluestem). Native species that may also be present in (and sometimes dominate) these sites include Panicum virgatum (switchgrass), Andropogon glomeratus (bushy bluestem), Elymus virginicus (Virginia wildrye), Nassella leucotricha (Texas wintergrass), Hordeum pusillum (little barley), Tripsacum dactyloides (eastern gamagrass), Muhlenbergia lindheimeri (Lindheimer's muhly), Carex spp. (carices), and Eleocharis spp. (spikerushes). Floodplain occurrences often include portions that resemble Edwards Plateau Riparian vegetation, especially along stream margins, where Platanus occidentalis (sycamore), Taxodium distichum (baldcypress), Juglans microcarpa (little walnut), Brickellia spp. (brickellbush), Cladium mariscus ssp. jamaicense (saw-grass), and Panicum virgatum (switchgrass) are frequently encountered.