Ecoregions of Texas, AS-199 - Texas Commission on Environmental ...

1825 High PlainsThe High Plains ecoregion is higher and drier than the Central Great Plains (27) to the east. And, in contrastto the characteristic irregular rangeland <strong>of</strong> the Northwestern Great Plains (43) to the north in the Dakotasand eastern Montana and Wyoming, much <strong>of</strong> the High Plains is expressed as smooth to slightly irregularplains with a high percentage <strong>of</strong> cropland. The potential natural vegetation in this region is grama-buffalograss compared to mostly wheatgrass-needlegrass to the north, Trans-Pecos shrub savanna to the south, andtallgrass prairie to the east (Kuchler 1964, 1970). The northern boundary <strong>of</strong> this ecological region is also theapproximate northern limit <strong>of</strong> winter wheat and sorghum and the southern limit <strong>of</strong> spring wheat. The ecoregionincludes the plains area <strong>of</strong> the Llano Estacado. Thousands <strong>of</strong> playa lakes (seasonal depressional wetlands)occur in this area, many serving as recharge areas for the important Ogallala Aquifer. These playa lakes arealso essential for waterfowl during their yearly migration along the Central Flyway <strong>of</strong> North America. Oil andgas production occurs in many parts <strong>of</strong> the region.25b Rolling Sand PlainsThe Rolling Sand Plains expand northward from the lip <strong>of</strong> the Canadian River trough,and they are topographically expressed as flat sandy plains or rolling dunes. Ecoregion25b is similar to the Canadian-Cimarron High Plains (25e) in that it has a more northerlyclimate with colder, more snowy winters than the rest <strong>of</strong> the Llano Estacado (25i) tothe south <strong>of</strong> the Canadian River. The vegetative cover <strong>of</strong> the Rolling Sand Plains istransitional between the Shinnery Sands (25j) to the south and the sandsage prairies <strong>of</strong>Oklahoma and Kansas (northerly disjunct polygons <strong>of</strong> Ecoregion 25b). Havard shin oak (Quercus havardii),the characteristic shrub cover <strong>of</strong> the Shinnery Sands (Ecoregion 25j), still grows in the <strong>Texas</strong> portion <strong>of</strong>Ecoregion 25b, but it is at the northern limit <strong>of</strong> its distribution.However, both Havard shin oak and sand sagebrush (Artemisiafilifolia) perform the same important function <strong>of</strong> stabilizingsandy areas subject to wind erosion.The boundaries for the Rolling Sand Plains were delineatedthrough a conjunction <strong>of</strong> the mapped sandsage association onvegetation maps and the soil maps and descriptions that identifiedtypically sandy soil associations (USDA NRCS <strong>199</strong>4). Thesesandy areas were also corroborated on topographical maps asareas that had a more random and irregular road network, ratherthan the rectangular grid that is common in agricultural areas.The sandsage association includes grasses such as big The sand shinnery (Quercus mohriana, Artemisiafilifolia) community protects the Rolling Sand Plainssandreed (Calamovilfa gigantea), little bluestem (Schizachyrium from wind erosion by vegetating the loose sandscoparium), sand dropseed (Sporobolus cryptandrus), and sand substrate. The rolling dune topography is visible in thebluestem (Andropogon gerardii). Other native range plants are background. Photo: R.E. Rosiere, Tarleton State University.blue grama (Bouteloua gracilis), sideoats grama (Boutelouacurtipendula), buffalograss (Buchloe dactyloides), switchgrass (Panicum virgatum),yellow Indiangrass (Sorghastrum nutans), and yucca (Yucca spp.). The soils <strong>of</strong> theRolling Sand Plains have a mesic temperature regime in contrast to the thermictemperature regime <strong>of</strong> soil in the Llano Estacado (25i) south <strong>of</strong> the Canadian River.Coarse textured sandy soils typically remain in native rangeland. Soils that are moreloamy or clayey may be tilled and planted with wheat or grain sorghum. The goal<strong>of</strong> both agricultural and grazing management is to keep enough vegetative cover onthe land surface to minimize wind erosion.The drainage density <strong>of</strong> the region is low, but thesandy surface serves as a recharge area for a minorgroundwater aquifer that feeds a few widely spaced<strong>Ecoregions</strong> <strong>of</strong> <strong>Texas</strong>The sand dropseed (Sporoboluscryptandrus) is a bunchgrassthat grows in the coarse sands<strong>of</strong> Ecoregion 25b. Photo: R.E.Rosiere, Tarleton State University