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

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the only chipmunk in <strong>Texas</strong>, the gray-footed chipmunk (Tamias canipes), are protected within GuadalupeMountains National Park. Elk (Cervus elaphus) were introduced in the 1920’s to replace an extinct subspecies,the Merriam elk, which was known in the region only from archeological evidence. The elk introduction wasnot without some controversy. In a report describing the benefits <strong>of</strong> adding the McKittrick Canyon area to theNational Park System, Wright et al., (1932) observed that the Rocky Mountain elk were an exotic addition tothe desert landscape, that they would concentrate their activities in the limited riparian habitats, and have anegative impact on the native vegetation. The report recommended that the elk be greatly reduced in numberor extirpated entirely if the area were to become a National Park. The elk population increased to 350 by themid 1960’s, but since then they have declined steadily to their original numbers (Schmidley 2002). Anotherintroduced mammal, the aoudad (Barbary sheep) (Ammotragus lervia), has taken over the ecological nicheonce occupied by desert bighorn sheep (Ovis canadensis), which had been eliminated from the GuadalupeMountains by 1910 (<strong>Texas</strong> State Historical Association 2002).Level IV Ecoregion23b. Montane WoodlandArea (sq. mi.) 16PhysiographyFault block mountain range dissected by deep canyons; Moderate gradientintermittent, flashy streams with mostly cobble, gravel, and sandy substrates.Elevation /Local Relief (feet)5,000-8000 /400-1200Pleistocene to Holocene clay loam colluvium mixed with limestone and sandstoneSurficial Geology;fragments, gypsum deposits; Pleistocene to Holocene gravels and sands in drainages.Bedrock GeologyPermian limestones, sandstones, and claystones.Soil Order (Great Groups) Mollisols (Calciustolls)Common Soil SeriesDeama, Rock outcrop.Soil Temperature /Soil Moisture RegimesMesic /UsticMean Annual Precipitation (in.) 18-22Mean Annual Frost Free Days 110-170Mean Temperature (F)(Jan. min/max; July min/max)VegetationLand Cover and Land Use29/52;62/85North-facing canyon slopes and upland locations above 7000 feet: Ponderosapine, southwestern white pine, Douglas-fir, limited aspen on talus slopes. Montanewoodland: pinyon pine, red-berry juniper, gray oak, Emory oak. Montane grassland:little bluestem, gramas, needlegrasses. Canyon riparian woodland: chinkapin oak,alligator juniper, bigtooth maple, <strong>Texas</strong> madrone, velvet ash.Patches <strong>of</strong> montane woodland, grassland, riparian woodland. Public land (GuadalupeMountains National Park), recreation, research.Guadalupe Mountains National Park is one<strong>of</strong> the few areas in <strong>Texas</strong> where the cougarhas protected status. However, even withunregulated hunting pressure outside the park,cougars are well-established in <strong>Ecoregions</strong> 23and 24. Photo: US Fish and Wildlife ServiceCanyon vegetation includes juniper, ash, oak, <strong>Texas</strong> madrone, and bigtoothmaple, with some ponderosa pine at higher elevations. Mule deer and elktend to concentrate in riparian areas, stripping the bark <strong>of</strong>f older trees andconsuming emerging seedlings. The <strong>Texas</strong> madrone is particularly vulnerableto browsing pressure. Photo: George Hosek<strong>Ecoregions</strong> <strong>of</strong> <strong>Texas</strong> 7
24 Chihuahuan DesertsThis desert ecoregion extends from the Madrean Archipelago (79) in southeastern Arizona to the EdwardsPlateau (30) in south-central <strong>Texas</strong>. It is the northern portion <strong>of</strong> the southernmost desert in North Americathat extends more than 500 miles south into Mexico. In much <strong>of</strong> the U.S. portion, the physiography <strong>of</strong> theregion is generally a continuation <strong>of</strong> basin and range terrain (excluding the Stockton Plateau) that is typical<strong>of</strong> the Mojave Basin and Range (14) and the Central Basin and Range (13) ecoregions to the west and north,although the pattern <strong>of</strong> alternating mountains and valleys is not as pronounced as it is in <strong>Ecoregions</strong> 13 and 14.The mountain ranges are a geologic mix <strong>of</strong> faulted limestone reefs, volcanoes and associated basalt and tuffextrusive rocks, and rhyolitic intrusions. Outside the major river drainages, such as the Rio Grande and PecosRiver, the landscape is largely internally drained. Vegetative cover is predominantly semi-desert grasslandand arid shrubland, except for high elevation islands <strong>of</strong> oak, juniper, and pinyon pine woodland. The extent<strong>of</strong> desert shrubland is increasing across lowlands and mountain foothills due to gradual desertification causedin part by historical grazing pressure.24a Chihuahuan Basins and PlayasThe boundaries for the Chihuahuan Basins and Playas ecoregion surround areas <strong>of</strong>lowest elevation in west <strong>Texas</strong> (under 1500 feet near the confluence <strong>of</strong> the Pecos andRio Grande rivers), alluvial basins near these rivers, and arid intermountain basins andsalt flats under 4500 feet. The boundaries <strong>of</strong> these disjunct areas are marked climaticallyby rainfall amounts between 8 and 14 inches, the lowest in the state, by soils that arealkaline or gypsiferous, and by desert shrub vegetation, predominantly creosote bush.The major Chihuahuan basins in Ecoregion 24a, such as the Hueco, Salt, and Presidio basins, formedduring the Basin and Range tectonism when the earth’s crust stretched, causing portions <strong>of</strong> the crust to collapsecreating deep depressions or grabens that filled with sediment over time. The sediments consist <strong>of</strong> clay, silt,sand, and gravel up to 9000 feet thick (such as in the Hueco basin) (Spearing <strong>199</strong>1). The flat arid floors <strong>of</strong>these basins (playas) have saline or alkaline soils and areas <strong>of</strong> white salt flats (former lake beds), dunes, andwindblown sand. Surrounding the playas at low elevations are miles <strong>of</strong> desert shrubland. These basins <strong>of</strong>tenlie in the rainshadow <strong>of</strong> nearby mountain ranges; they represent the hottest and driest habitats in <strong>Texas</strong>, withless than 14 inches <strong>of</strong> precipitation per year. Winter precipitation is relatively sparse; precipitation amountsare highest during the monsoonal rains <strong>of</strong> July, August, and September.The desert flora must withstand large diurnal ranges in temperature, low available moisture, and anextremely high evapotranspiration rate. The highly saline portion <strong>of</strong> the playas at the lowest elevations, maybe completely barren, but salt-tolerant plants such as fourwing saltbush (Atriplex canescens), pickleweed(Allenrolfea occidentalis), and alkali sacaton(Sporobolus airoides) do grow in the margins<strong>of</strong> the dry lake beds where the water table isnear the surface (Bezanson 2000). The valleysand rolling alluvial fans above the basin floorssupport vast areas <strong>of</strong> desert shrubs dominatedby creosote bush (Larrea tridentata) andtarbush (Flourensia cernua). Land use forgrazing has evolved from cattle to sheepand goats as the range has changed from apredominance <strong>of</strong> grass to desert shrubs.Creosote bushes grow on alkaline flats in evenly spaced rows with theirpositions relative to one another determined by water availability. Theseshrubs are also allelopathic, meaning they release toxins into the surroundingsoil that discourage competition from neighboring plants. Photo: Sandy BryceThe low elevation desert country <strong>of</strong> thePecos River basin and the Rio Grande Riverbasin bound West <strong>Texas</strong> on the east, south,and west. Both rivers carry water into theregion from sources in the Rocky Mountains8<strong>Ecoregions</strong> <strong>of</strong> <strong>Texas</strong>
Page 1: Below is an Electronic Version <str
Page 4 and 5: ECOREGIONS OF TEXAS</strong
Page 6 and 7: TABLE OF CONTENTSABSTRACT..........
Page 8 and 9: 2526272526272330293235332430323423
Page 10 and 11: INTRODUCTIONSpatial frameworks are
Page 12 and 13: Maps of environmen
Page 14 and 15: vegetation or small areas o
Page 18 and 19: to the north. There is a high deman
Page 20 and 21: taller, coarser tobosa grass (Pleur
Page 22 and 23: the fractured rock. The Bof
Page 24 and 25: hollows, moving upslope to create c
Page 26 and 27: The headwater catfish (Ictalurus lu
Page 28 and 29: streams. Two sand plains streams, C
Page 30 and 31: Several caliche horizons (calcium c
Page 32 and 33: winds (Spearing 199</strong
Page 34 and 35: Geology is an important geographica
Page 36 and 37: the villages of Pa
Page 38 and 39: Area (sq. mi.) 5569PhysiographyFlat
Page 40 and 41: Tableland topography of</st
Page 42: y the Brazos and Colorado rivers ha
Page 45 and 46: Level IV Ecoregion27i. Broken Red P
Page 47 and 48: Post oaks (Quercus stellata) and bl
Page 49 and 50: Level IV Ecoregion29c. Western Cros
Page 51 and 52: than the limestone of</stro
Page 53 and 54: underlying the sandstone. This has
Page 55 and 56: Since settlement, many wildlife spe
Page 57 and 58: (Pellaeae spp.), Nuttall’s stonec
Page 59 and 60: Trinity-Edwards aquifer, discharges
Page 61 and 62: Edwards Plateau to savanna-like con
Page 63 and 64: species list, prefers fast moving w
Page 65 and 66: Level IV Ecoregion31a. Northern Nue
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31c Texas-Tamaulip
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31d Rio Grande Floodplain and Terra
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62shrink when dry and swell when we
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32b Southern Blackland PrairieThe S
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33 EAST CENTRAL TE
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and need some patchy distubances an
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33d Northern Prairie OutliersThe sm
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Level IV Ecoregion33e. Bastrop Lost
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34a Northern Humid Gulf Coastal Pra
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34b Southern Subhumid Gulf Coastal
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occasional discontinuous drainage r
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oundary was the ability to match th
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Level IV Ecoregion34f. Lower Rio Gr
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live oak trees (Quercus virginiana)
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Shoal grass (Halodule wrightii) mea
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Upland oak-pine forest in Ecoregion
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35c Pleistocene Fluvial TerracesThe
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35f FlatwoodsMostly flat to gently
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pasture, although some woodland sti
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invariant definition of</st
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how many stream sites/watersheds ar
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commonly believed. Typically, about
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CONCLUSIONS AND RECOMMENDATIONSThis
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104Ecoregions <str
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Biggs, B.J.F., M.J. Duncan, I.G. Jo
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Diggs, G.M., Jr., and P.C. Schulze.
Page 119 and 120:
Graves, J. 2002. Texas</str
Page 121 and 122:
Hunt, C.B. 1967. Physiography <stro
Page 123 and 124:
Maxwell, T.C. 1979. Avifauna <stron
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Richmond, G.M., D.L. Weide, and D.W
Page 127 and 128:
U.S. Department of
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Woods, A.J., J.M. Omernik, D.R. But
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Herbaceous Plants(Forbs, Grasses, a
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Hickory, BlackHickory, WaterHollyHu
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