Natural Resources
Conservation Service
Ecological site R042AE274TX
Mountain Valley Foothill Slope, Mixed Prairie
Last updated: 8/10/2020
Accessed: 11/21/2024
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
Ecological site concept
• Site receives sheet-flow run-on water from higher elevation sites and sheds run-off water to lower elevation sites
• Site Landform: fan remnants and stream terraces of mountain valley
• Elevation Range: 4,500' to 6,700'
• Slope Range: 1-30%
• Soils:
- Particle Size Class: loamy
- Surface textures include gravelly loam, very gravelly loam, and cobbly loam
- Soil Depth: shallow to very deep
- Fragments on the Surface: 40-95%
- Parent Material: alluvium derived from igneous rock
• Moisture Regime: dry ustic
• Temperature Regime: thermic
• Dominant Cover: rangeland (grassland)
Associated sites
| R042AC244TX |
Gravelly, Desert Grassland This site is occurs downslope on lower piedmont slopes. |
|---|---|
| R042AE277TX |
Igneous Hill and Mountain, Mixed Prairie This site occurs at higher position and is a source of alluvial material. |
Similar sites
| R042AF284TX |
Foothill Slope, Mountain Savannah This site occurs in the same landscape position but at a higher elevation range. |
|---|
Table 1. Dominant plant species
| Tree |
Not specified |
|---|---|
| Shrub |
Not specified |
| Herbaceous |
Not specified |
Physiographic features
The site occurs on alluvial fans and terraces in mountain valleys. Up to four geomorphic components can occur within the site. From highest to lowest, the components are erosional fan remnant summit, erosional fan remnant footslope, inset fan, and channel floor. Slopes range from 1- 30 percent. Runoff ranges from medium to high.
Table 2. Representative physiographic features
| Landforms |
(1)
Mountain valleys or canyons
> Fan remnant
(2) Mountain valleys or canyons > Terrace |
|---|---|
| Flooding frequency | None |
| Ponding frequency | None |
| Elevation | 4,500 – 6,700 ft |
| Slope | 1 – 30% |
| Aspect | Aspect is not a significant factor |
Climatic features
The average annual precipitation ranges from 15 to 18 inches and the total annual precipitation is highly variable, ranging from 8 to 30 inches. Most of the precipitation occurs as widely scattered thunderstorms of high intensity and short duration during the summer. Occasional precipitation occurs as light rainfall during the cool season. Annual snowfall ranges from 1-3 inches.
Mean annual air temperature is 61° F. Frost-free period ranges from 201 to 206 days (April-October). However, the optimal growing season occurs July through September as this period coincides with greater rainfall.
The average relative humidity in mid-afternoon is about 25 percent. Relative humidity is higher at night, and the average at dawn is about 57 percent. The sun shines 81 percent of the time in summer and 75 percent in winter. The prevailing wind is from the southwest. Average wind speed is highest, around 11 miles per hour, in March and April. The annual Class-A pan evaporation is approximately 82 inches.
Table 3. Representative climatic features
| Frost-free period (characteristic range) | 202-205 days |
|---|---|
| Freeze-free period (characteristic range) | 221-232 days |
| Precipitation total (characteristic range) | 15-18 in |
| Frost-free period (actual range) | 201-206 days |
| Freeze-free period (actual range) | 219-234 days |
| Precipitation total (actual range) | 14-19 in |
| Frost-free period (average) | 204 days |
| Freeze-free period (average) | 227 days |
| Precipitation total (average) | 17 in |
Figure 2. Monthly precipitation range
Figure 3. Monthly minimum temperature range
Figure 4. Monthly maximum temperature range
Figure 5. Monthly average minimum and maximum temperature
Figure 6. Annual precipitation pattern
Figure 7. Annual average temperature pattern
Climate stations used
-
(1) CHISOS BASIN [USC00411715], Big Bend National Park, TX
-
(2) PANTHER JUNCTION [USC00416792], Big Bend National Park, TX
Influencing water features
• Site receives sheet-flow run-on water from higher elevation sites and sheds run-off water to lower elevation sites
• No wetlands or perennial streams influence this site
Soil features
The site consists of shallow to very deep, well drained, gravelly to cobbly soils with a loamy surface texture. The soils consist of three series formed in alluvium weathered from igneous bedrock:
The associated soil series for this ecological site in Big Bend National Park in Brewster County includes the Hurds (dry phase) series. The Hurds series formed in very gravelly, late Pleistocene-age pedisediments on footslopes (pediments) of erosion fan remnants. Diagnostic horizons contained within the soil include a mollic epipedon and a loamy-skeletal argillic horizon.
The representative soils and their associated map units are:
Big Bend National Park Soil Survey:
Hurds very cobbly loam, 10 to 30 percent slopes
Table 4. Representative soil features
| Surface texture |
(1) Gravelly loam (2) Very gravelly loam (3) Cobbly loam |
|---|---|
| Family particle size |
(1) Loamy |
| Drainage class | Well drained |
| Permeability class | Moderate |
| Soil depth | 14 – 80 in |
| Surface fragment cover <=3" | 20 – 50% |
| Surface fragment cover >3" | 20 – 45% |
| Available water capacity (0-40in) |
1 in |
| Calcium carbonate equivalent (0-40in) |
1% |
| Electrical conductivity (0-40in) |
Not specified |
| Sodium adsorption ratio (0-40in) |
Not specified |
| Soil reaction (1:1 water) (0-40in) |
6.1 – 7.8 |
| Subsurface fragment volume <=3" (Depth not specified) |
25 – 40% |
| Subsurface fragment volume >3" (Depth not specified) |
8 – 30% |
Ecological dynamics
The Historic Climax Plant Community (HCPC) for the site is composed primarily of a diversity of short and midgrasses, numerous perennial forbs, and scattered trees and shrubs. The distribution of vegetation within the site is highly dependent on local environment. Elevation gradients, landscape position, aspect, and variability of the soils, are the major factors driving species composition and distribution. Water can concentrate in small drains as it crosses this site and an axial drainageway in the valley bottom. Both of these result in denser vegetation.
Historically, the site has evolved with native herbivores such as mule deer and possibly desert bighorn sheep. Bison were not documented in the historical record as being present in any significant amount. A lack of sufficient water was probably a contributing factor. Small lightning induced fires were likely common mainly because of the adequate amount of fine fuels present.
Early records suggest cattle, sheep, and horses were introduced into the southwest from Mexico in the mid-1500's. However, extensive ranching began in the Trans-Pecos region in the 1880s. Records indicate cattle, sheep, and goats grazed this site extensively during the early to mid 1900s. Direct fire suppression and overutilization of plant resources in some areas most likely began during this time.
The impact of improper grazing within this site will lead to a reduction of palatable grasses and forbs and an increase of woody plants such as mariola and various acacias. In addition, direct fire suppression will also allow woody plants to increase.
The following diagram suggests general pathways that the vegetation on this site might follow. There are other plant communities and states not shown on the diagram. This information is intended to show what might happen in a given set of circumstances; it does not mean that this would happen the same way in every instance. Local professional guidance should always be sought before pursuing a treatment scenario.
State and Transition Model
State and transition model
Figure 8. MLRA 42 - Foothill Slope (Mixed Prairie) - STM Dia
More interactive model formats are also available.
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More interactive model formats are also available.
View Interactive Models
Click on state and transition labels to scroll to the respective text
Ecosystem states
State 1 submodel, plant communities
State 2 submodel, plant communities
State 1
Grassland State
Community 1.1
Short/Midgrass Dominant Community
Figure 9. Short/Midgrass Dominant Community
The distribution of vegetation within the site is highly dependent on local environment. Elevation gradients, landscape position, aspect, and variability of the soils are the major factors driving species composition and distribution. The Historic Climax Plant Community (HCPC) for the site is composed primarily of a diversity of short and midgrasses, numerous perennial forbs, and scattered trees and shrubs and is the reference plant community. Plants more adaptable to drier conditions such as chino grama, lechuguilla, and pricklypear are most commonly found at low elevations, in convex positions, and/or in shallow soils. Plants more adapted to moist conditions such as evergreen and littleleaf sumac, hairy grama, juniper, and oak are most commonly found at higher elevations, in concave positions and/or in deeper soils. Since the site is located in a water receiving and shedding position and at a relatively high overall elevation, shrub encroachment following grass overutilization can occur quickly. Palatable grasses such as blue, black, and sideoats grama, Arizona cottontop, and, bristlegrass are replaced by shrubs such as mariola, several acacia species, lechuguilla, and grasses such as slim tridens, fluffgrass, and threeawns. Brush management tools such as prescribed fire, mechanical or chemical control, and prescribed grazing can help maintain the community within the reference state. Extensive overutilization of plant resources by livestock will transition the reference plant community to the Shrubland State (2). Droughts can expedite the change.
Figure 10. Annual production by plant type (representative values) or group (midpoint values)
Table 5. Annual production by plant type
| Plant type | Low (lb/acre) |
Representative value (lb/acre) |
High (lb/acre) |
|---|---|---|---|
| Grass/Grasslike | 640 | 880 | 1120 |
| Shrub/Vine | 96 | 132 | 168 |
| Forb | 40 | 55 | 70 |
| Tree | 24 | 33 | 42 |
| Total | 800 | 1100 | 1400 |
Figure 11. Plant community growth curve (percent production by month). TX4009, Mid/Shortgrasses Dominant with Shrubs Community. Mid and shortgrasses dominate the community with shrubs approaching 20% woody canopy..
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| J | F | M | A | M | J | J | A | S | O | N | D |
| 2 | 2 | 2 | 2 | 3 | 8 | 8 | 18 | 23 | 15 | 15 | 2 |
State 2
Shrubland State
Community 2.1
Shrub Dominant Community
Figure 12. Shrub Dominant Community
Figure 13. Shrub Dominant Community
Figure 14. Shrub Dominant Community
This plant community is the result of extensive overutilization of plant resources by livestock and direct fire suppression. Improper grazing management reduces the amount of palatable midgrasses and fine fuels needed for natural fires to occur. This provides a competitive advantage to woody plants. The most prevalent woody plants that increase under these conditions are mariola, lechuguilla, broomweed, and several acacia species. Palatable grasses such as black grama, sideoats grama, and Arizona cottontop decrease. Fluffgrass and slim tridens increase following disturbance. Proper grazing management (adequate rest to allow recovery of some grasses) followed by prescribed fire and/or brush management will help transition the community back to a composition similar to the reference plant community. Brush management strategies may include grubbing and/or chemical herbicide application or most likely a combination of methods over time. Poor accessibility may limit brush management methods in some areas.
Figure 15. Annual production by plant type (representative values) or group (midpoint values)
Table 6. Annual production by plant type
| Plant type | Low (lb/acre) |
Representative value (lb/acre) |
High (lb/acre) |
|---|---|---|---|
| Shrub/Vine | 520 | 715 | 910 |
| Grass/Grasslike | 200 | 275 | 350 |
| Forb | 35 | 55 | 70 |
| Tree | 40 | 55 | 70 |
| Total | 795 | 1100 | 1400 |
Figure 16. Plant community growth curve (percent production by month). TX4004, Shrub Dominant Community. The major woody increaser species, such as lechuguilla, ocotillo, sotol, acacia, and creosotebush, have multiplied. Very little shortgrasses remaining..
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| J | F | M | A | M | J | J | A | S | O | N | D |
| 1 | 1 | 2 | 2 | 2 | 8 | 8 | 20 | 25 | 15 | 15 | 1 |
Transition T1A
State 1 to 2
With fire suppression and improper grazing management, the Grassland State converts to Shrubland State.
Restoration pathway R2A
State 2 to 1
With Prescribed Burning, Brush Management, and Proper Grazing Management, the Shrubland State can be restored to Grassland State.
Conservation practices
| Brush Management | |
|---|---|
| Prescribed Burning | |
| Prescribed Grazing |
Additional community tables
Table 7. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (lb/acre) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Grass/Grasslike
|
||||||
| 1 | Warm-season midgrasses | 240–420 | ||||
| sideoats grama | BOCU | Bouteloua curtipendula | 140–350 | – | ||
| cane bluestem | BOBA3 | Bothriochloa barbinodis | 100–250 | – | ||
| 2 | Warm-season short/midgrasses | 200–350 | ||||
| black grama | BOER4 | Bouteloua eriopoda | 75–200 | – | ||
| blue grama | BOGR2 | Bouteloua gracilis | 75–200 | – | ||
| bush muhly | MUPO2 | Muhlenbergia porteri | 50–100 | – | ||
| 3 | Warm-season midgrasses | 120–210 | ||||
| Arizona cottontop | DICA8 | Digitaria californica | 45–125 | – | ||
| tanglehead | HECO10 | Heteropogon contortus | 45–125 | – | ||
| green sprangletop | LEDU | Leptochloa dubia | 30–100 | – | ||
| 4 | Warm-season mid/shortgrasses | 40–70 | ||||
| threeawn | ARIST | Aristida | 12–50 | – | ||
| slim tridens | TRMU | Tridens muticus | 12–50 | – | ||
| streambed bristlegrass | SELE6 | Setaria leucopila | 10–40 | – | ||
| plains lovegrass | ERIN | Eragrostis intermedia | 5–25 | – | ||
| 5 | Warm-season mid/shortgrasses | 24–42 | ||||
| common wolfstail | LYPH | Lycurus phleoides | 10–20 | – | ||
| hairy grama | BOHI2 | Bouteloua hirsuta | 10–20 | – | ||
| Chino grama | BORA4 | Bouteloua ramosa | 0–20 | – | ||
| low woollygrass | DAPU7 | Dasyochloa pulchella | 4–12 | – | ||
| 6 | Warm-season mid/tallgrasses | 16–28 | ||||
| Texas bluestem | SCCI2 | Schizachyrium cirratum | 5–15 | – | ||
| little bluestem | SCSCS | Schizachyrium scoparium var. scoparium | 5–15 | – | ||
|
Shrub/Vine
|
||||||
| 7 | Shrubs | 40–70 | ||||
| resinbush | VIST | Viguiera stenoloba | 10–40 | – | ||
| littleleaf ratany | KRER | Krameria erecta | 8–20 | – | ||
| littleleaf sumac | RHMI3 | Rhus microphylla | 5–15 | – | ||
| stretchberry | FOPU2 | Forestiera pubescens | 5–15 | – | ||
| woolly butterflybush | BUMA | Buddleja marrubiifolia | 5–15 | – | ||
| featherplume | DAFO | Dalea formosa | 5–15 | – | ||
| jointfir | EPHED | Ephedra | 3–10 | – | ||
| evergreen sumac | RHVI3 | Rhus virens | 3–10 | – | ||
| 8 | Shrubs | 32–56 | ||||
| whitethorn acacia | ACCO2 | Acacia constricta | 3–10 | – | ||
| catclaw acacia | ACGR | Acacia greggii | 3–10 | – | ||
| whitebrush | ALGR2 | Aloysia gratissima | 3–8 | – | ||
| catclaw mimosa | MIACB | Mimosa aculeaticarpa var. biuncifera | 2–8 | – | ||
| mariola | PAIN2 | Parthenium incanum | 3–8 | – | ||
| western honey mesquite | PRGLT | Prosopis glandulosa var. torreyana | 2–6 | – | ||
| spiny hackberry | CEEH | Celtis ehrenbergiana | 0–5 | – | ||
| creosote bush | LATR2 | Larrea tridentata | 1–5 | – | ||
| rough menodora | MESC | Menodora scabra | 1–3 | – | ||
| 9 | Fibrous/Succelents | 24–42 | ||||
| sotol | DASYL | Dasylirion | 5–15 | – | ||
| pricklypear | OPUNT | Opuntia | 5–15 | – | ||
| yucca | YUCCA | Yucca | 3–8 | – | ||
| Texas sacahuista | NOTE | Nolina texana | 3–8 | – | ||
| tree cholla | CYIMI | Cylindropuntia imbricata var. imbricata | 3–8 | – | ||
| Christmas cactus | CYLE8 | Cylindropuntia leptocaulis | 3–8 | – | ||
| lechuguilla | AGLE | Agave lechuguilla | 0–5 | – | ||
|
Tree
|
||||||
| 10 | Trees | 24–42 | ||||
| juniper | JUNIP | Juniperus | 12–25 | – | ||
| oak | QUERC | Quercus | 12–25 | – | ||
|
Forb
|
||||||
| 11 | Forbs | 40–70 | ||||
| Forb, dicot, perennial | 2FDP | Forb, dicot, perennial | 15–30 | – | ||
| Forb, annual | 2FA | Forb, annual | 0–10 | – | ||
| awnless bushsunflower | SICA7 | Simsia calva | 5–8 | – | ||
| white sagebrush | ARLUM2 | Artemisia ludoviciana ssp. mexicana | 5–8 | – | ||
| croton | CROTO | Croton | 5–8 | – | ||
| low silverbush | ARHU5 | Argythamnia humilis | 2–4 | – | ||
| globemallow | SPHAE | Sphaeralcea | 2–4 | – | ||
| lacy tansyaster | MAPI | Machaeranthera pinnatifida | 1–3 | – | ||
| polygala | POLYG | Polygala | 1–3 | – | ||
| golden prairie clover | DAAU | Dalea aurea | 1–3 | – | ||
| pepperweed | LEPID | Lepidium | 0–2 | – | ||
Interpretations
Animal community
The site is suitable for properly managed (appropriate stocking rates) livestock grazing. Improper grazing management causes a gradual decline in range health reducing livestock nutrition and habitat quality for wildlife. Livestock should be stocked at or below carrying capacity in proportion to the grazeable grass, forbs, and browse. When the slopes on this site approach >15 percent, cattle use becomes limited. Grazing distribution will be an issue in these cases.
The site supports a high diversity of wildlife species. Mammals that that use this site for at least a portion of their overall habitat needs include mule deer, javelinas, bobcats, coyotes, black-tailed jackrabbits, cottontails, raccoons, ringtails, gray foxes, and ground squirrels. Birds that use this site as year-round habitat, a stopover area during migration, nesting grounds, and/or wintering grounds include scaled quail, dove, raptors, and numerous song birds.
Plant Preference by Animal Kind:
These preferences are somewhat general in nature as the preferences for plants is dependent upon grazing experience, time of year, availability of choices, and total forage supply.
Legend: P=Preferred D=Desirable U=Undesirable N=Not Consumed T=Toxic X=Used, but not degree of utilization unknown
Preferred – Percentage of plant in animal diet is greater than it occurs on the land
Desirable – Percentage of plant in animal diet is similar to the percentage composition on the land
Undesirable – Percentage of plant in animal diet is less than it occurs on the land
Not Consumed – Plant would not be eaten under normal conditions. Only consumed when other forages not available.
Toxic – Rare occurrence in diet and, if consumed in any tangible amounts results in death or severe illness in animal
Hydrological functions
The existing plant community with representative plant species, current soil conditions (soil health), land management, and climate affect the dynamics of the water cycle. Plant and litter cover are important factors which protect the site from erosion. However, it is total production and the types of plant species present that have greatest impact on hydrologic dynamics (infiltration capacity, runoff, and soil losses).
Livestock overgrazing can reduce the amount of perennial, deep-rooted mid and tall grasses. This can then lead to soil erosion by increasing overland flow and decreasing infiltration rates.
Recreational uses
The site is suitable for hiking and camping.
Wood products
None.
Other products
None.
Other information
None.
Supporting information
Inventory data references
Information presented here has been developed from NRCS clipping, composition, plant cover, and soils data. Where empirical data is limiting, technical interpretations were made based of field experience.
Other references
Briske, D.D., J.D. Derner, J.R. Brown, S.D. Fuhlendorf, W.R. Teague, K.M. Havstad, R.L. Gillen, A.J. Ash, and W.D. Williams. 2008. Rotational grazing on rangelands: Reconciliation of perception and experimental evidence. Rangeland Ecology and Management 61: 3-17.
Peterson, F.F. 1981. Landforms of the basin and range province: Defined for soil survey. Technical Bulletin 28. Nevada Agricultural Experiment Station, University of Nevada, Reno.
Powell, M.A. 2000. Grasses of the Trans-Pecos and Adjacent Areas. Iron Mountain Press, Marathon, TX.
Powell, M.A. 1998. Trees and shrubs of the Trans-Pecos and adjacent areas. University of Texas Press, Austin.
USDA, National Water and Climate Center, “Climate Reports,” http://www.wcc.nrcs.usda.gov/climate/ (accessed January 2007).
USDA, Natural Resources Conservation Service, “Plants Database,” http://plants.usda.gov/ (accessed October 2008).
Warnock, B.H. 1977. Wildflowers of the Davis Mountains and Marathon Basin Texas. Sul Ross State University, Alpine, TX.
Reviewers:
Jim Clausen, Soil Scientist, NRCS, Marfa, TX
Lynn Loomis, Soil Scientist, NRCS, Marfa, TX
Laurie Meadows, Soil Conservation Technician, NRCS, Marfa, TX
Mark Moseley, Rangeland Management Specialist, NRCS, San Antonio, TX
Contributors
Michael Margo, RMS, NRCS, Marfa, Texas
Unknown
Approval
Scott Woodall, 8/10/2020
Rangeland health reference sheet
Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.
| Author(s)/participant(s) | |
|---|---|
| Contact for lead author | |
| Date | 09/07/2022 |
| Approved by | Scott Woodall |
| Approval date | |
| Composition (Indicators 10 and 12) based on | Annual Production |
Indicators
-
Number and extent of rills:
-
Presence of water flow patterns:
-
Number and height of erosional pedestals or terracettes:
-
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
-
Number of gullies and erosion associated with gullies:
-
Extent of wind scoured, blowouts and/or depositional areas:
-
Amount of litter movement (describe size and distance expected to travel):
-
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
-
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
-
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
-
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
-
Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):
Dominant:
Sub-dominant:
Other:
Additional:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
-
Average percent litter cover (%) and depth ( in):
-
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
-
Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
-
Perennial plant reproductive capability:
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