Natural Resources
Conservation Service
Ecological site R081DY297TX
Gravelly 8-14 PZ
Last updated: 9/19/2023
Accessed: 08/29/2026
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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.
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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.
MLRA notes
Major Land Resource Area (MLRA): 081D–Southern Edwards Plateau
This area is underlain primarily by limestones in the Austin Chalk, Boquillas Flags, Devil’s River, Santa Elena, Buda, and Del Rio Clay Formations of Cretaceous age. Quaternary sand and gravel are in the river valleys.
The 81D is in the hyperthermic thermic zoneClassification relationships
USDA-NRCS Ag Handbook 296
Ecological site concept
The site consists of very shallow to very deep soils that formed in gravelly alluvium derived from limestone bedrock. Soils with restrictive layers such as a petrocalcic horizon will have very slow permeability in these layers. This site is characterized by warm-season bunch grasses, stoloniferous grass, with scattered shrubs and a variety of forbs.
Associated sites
R042AB264TX Igneous Hill and Mountain, Hot Desert Shrub
The Gravelly 8-14” PZ will be found below Igneous Hill and Mountain Desert Shrub.
R042AB737TX Limestone Hill and Mountain, Hot Desert Shrub
The Gravelly 8-14” PZ does not have the limestone rocks in the surface.
R081DY295TX Flagstone Hill 8-14 PZ
The Flagstone Hill site has channers and flagstones on the surface and in the soil profile.
R081DY592TX Limestone Hill 8-14 PZ
The Limestone Hill site has cobbles and stones along with the gravels.
Similar sites
R042AC244TX Gravelly, Desert Grassland
The Gravelly (DG) is found at higher elevations and slightly more production.
Table 1. Dominant plant species
Tree Not specified
Shrub (1) Larrea tridentata
Herbaceous (1) Bouteloua ramosa
Physiographic features
The Gravelly Ecological Site consists of soils that are very deep and soils that are very shallow and shallow to a restrictive layer such as a petrocalcic horizon, shale, or tuff parent material. They formed in calcareous loamy materials containing gravel from mixed sources. These soils are on nearly level, hilly uplands fan piedmonts. Slope ranges from 0 to 30 percent. Elevations range from 1100 to 4000 feet.
Table 2. Representative physiographic features
Landforms (1) Piedmont slope > Inset fan
(2) Piedmont slope > Fan remnant
(3) Piedmont slope > Alluvial fan
(4) Plateau > Ridge
Runoff class Low to very high Flooding frequency None Ponding frequency None Elevation 1100 – 4000 ft Slope 0 – 30 % Aspect Aspect is not a significant factor Climatic features
The average annual precipitation ranges from 8 to 14 inches. The annual total can vary from two to 21 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. Negligible amounts of precipitation falls in the form of sleet or snow.
Mean annual air temperature is 70° F. Daytime temperatures exceeding 100° F are common from May through September. Frost-free period ranges from 246 to 256 days. Freeze-free period ranges from 277 to 290 days.
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 combination of low rainfall and relative humidity, warm temperatures, and high solar radiation creates a significant moisture deficit. The annual Class-A pan evaporation is approximately 94 inches.Table 3 Representative climatic features
Frost-free period (characteristic range) 240-280 days Freeze-free period (characteristic range) 270-300 days Precipitation total (characteristic range) 10-20 in Frost-free period (actual range) 240-280 days Freeze-free period (actual range) 270-300 days Precipitation total (actual range) 10-20 in Frost-free period (average) 260 days Freeze-free period (average) 280 days Precipitation total (average) 10 in Characteristic rangeActual rangeBarLineFigure 2. Monthly precipitation range
Characteristic rangeActual rangeBarLineFigure 3. Monthly minimum temperature range
Characteristic rangeActual rangeBarLineFigure 4. Monthly maximum temperature range
BarLineFigure 5. Monthly average minimum and maximum temperature
Figure 6. Annual precipitation pattern
Figure 7 Annual average temperature pattern
Climate stations used
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(1) LANGTRY [USC00415048], Comstock, TX
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(2) DRYDEN TERRELL CO AP [USW00003032], Dryden, TX
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(3) PERSIMMON GAP [USC00416959], Big Bend National Park, TX
">Influencing water features
None.
Wetland description
N/A
Soil features
The site consists of very shallow to very deep soils that formed in gravelly alluvium derived from limestone bedrock. Soils with restrictive layers such as a petrocalcic horizon will have very slow permeability in these layers. Runoff is low to medium on slopes less than 1 percent and very high on slopes greater than 20 percent.
The associated soil series include Strawhouse and Stillwell.
This soil is classified as “Hyperthermic”, meaning that the Mean Annual Soil Temperature typically measured at 20 inches depth is >72 degrees F based on the summary of a 5-year soil temperature study near La Linda, Texas.Table 4. Representative soil features
Parent material (1) Alluvium – limestone
Surface texture (1) Very gravelly coarse sandy loam
(2) Very gravelly sandy loam
(3) Very gravelly fine sandy loam
(4) Very gravelly loam
Family particle size (1) Loamy-skeletal
Drainage class Well drained Permeability class Very slow to moderate Depth to restrictive layer 10 – 80 in Soil depth 10 – 80 in Surface fragment cover <=3" 42 – 70 % Surface fragment cover >3" 2 – 16 % Available water capacity
(0-40in)1 – 2 in Calcium carbonate equivalent
(0-40in)35 – 80 % Electrical conductivity
(0-40in)0 – 4 mmhos/cm Sodium adsorption ratio
(0-40in)0 – 5 Soil reaction (1:1 water)
(0-40in)7.9 – 8.4 Subsurface fragment volume <=3"
(4-40in)30 – 60 % Subsurface fragment volume >3"
(4-40in)5 – 20 % Ecological dynamics
The reference plant community on the Gravelly 8-14” PZ ecological site consists of bunch and stoloniferous grasses along with a variety of perennial forbs and woody shrubs.
Probably the factor that most influenced the historic vegetative composition of the site was extended dry weather. High rainfall events did occur but were episodic. However, insects and grazers such as rodents, deer, and infrequent fire certainly played a part. Bison were not documented in the historical record as being present in any significant amount. A lack of water was probably a contributing factor. The perennial grasses dominating the site could survive the periodic droughts as long as the density of woody plants did not become excessive, and top-removal of the grass plants did not occur too frequently. Overgrazing amplifies the effects of drought.
Early historical records do not always provide information specific to a site but can provide insight as to conditions existing in a general vicinity. Accounts suggest cattle, sheep, and horses were introduced into the southwest from Mexico in the mid-1500s. However, extensive ranching did not begin in the Trans-Pecos region until the 1880s. Early explorers described the vegetation as they traveled over parts of the Trans-Pecos. For instance, Captain John Pope in 1854 described a portion of the Trans-Pecos area as “…destitute of wood and water, except at particular points, but covered with a luxuriant growth of the richest and most nutritious grasses known to this continent…”. Other early travelers describe the scattered springs and water sources that were found in the region. Wagon travel could only be accomplished, along trails that had both water and forage sufficient for overnight stops. Livestock numbers peaked in the late 1880s following the arrival of railroads. Some historical accounts document ranches with stocking rates as high as one animal unit per four acres; however, this was far from sustainable in this environment.
Decades of overgrazing with loss of vegetation and erosion make it a slow process to return to the reference community. In 1944 the southernmost portion of the Trans-Pecos area was set aside as Big Bend National Park. Grazing activities with livestock ceased. For example, in 1944, most of the Gravelly ecological sites accessible to livestock were probably degraded and dominated by woody shrubs. After 60 years of no grazing, the majority of sites have not recovered to the historic plant community which provides insight into the length of time it takes for recovery in this environment.
The large livestock herds brought in during the favorable years, mainly sheep, could not be sustained during the drought. Overgrazing became a major issue as the extended dry weather was a harsh taskmaster to the early stock growers.
Cattle use on rangeland declines significantly on slopes steeper than 15 percent, however cattle numbers were never very large. Sheep and goats are however able to utilize slopes up to about 45 percent and can negotiate the surface rock cover better than cattle. It should be noted that abusive grazing by different kinds and classes of livestock will result in different impacts on the site. One effect of the removal of vegetated cover was to expose bare ground to erosion. Another effect was the deterioration of perennial grasses which removed the source of fine fuel to sustain periodic fires. More than likely, fires were not very frequent and when they did occur, the burn pattern was a mosaic governed by terrain and vegetative features.
The following diagram suggests general pathways that the vegetation on this site might follow. There may be other states not shown in 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
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
T1A - Prolonged drought coupled with excessive grazing pressure State 1 submodel, plant communities
State 2 submodel, plant communities
State 1
ReferenceThe reference state is considered to be representative of the natural range of variation under pre-Euro settlement conditions. It is characterized by a diverse mixture of warm-season grasses and shrubs. Community phase changes are primarily driven by prolonged drought.
Dominant plant species
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Chino grama (Bouteloua ramosa), grass
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bush muhly (Muhlenbergia porteri), grass
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black grama (Bouteloua eriopoda), grass
Community 1.1
1.1 Midgrass/Shrub CommunityThe Midgrass/Shrub Community (1.1) is the reference plant community for the Gravelly 8-14” PZ Ecological Site. Grasses total approximately 70% of the species composition by air dry weight, while shrubs and forbs account for 25% and 5% respectively. Chino grama dominates the midgrasses along with a diversity of other palatable mid and shortgrasses. Creosotebush is the most common shrub as it thrives in gravelly and calcareous soils. A diversity of subshrubs, succulents, and forbs are also present. The characteristically high surface cover of gravels of the site helps reduce soil erosion. The diversity of plants provides necessary food and cover for native wildlife.
Extended dry weather causes an overall decline in grass cover and production and can cause some retrogression. However, the reference community evolved with plants that have drought tolerance. Long term retrogression is triggered primarily by abusive grazing which causes an immediate decrease and eradication of the most palatable plants black grama, sideoats grama, Arizona cottontop, and bush muhly. Resulting from the inherently low production potential of the site, shrub encroachment following grass removal is slow. Annual forbs, grasses, and succulents are the first to increase following a decrease in perennial grass cover
Conservation practices such as prescribed grazing can help maintain ecological integrity in the reference community. Stocking rates need to be flexible and adjusted to carrying capacity because of sporadic rainfall.Figure 8. 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 140 245 350 Shrub/Vine 50 87 125 Forb 10 18 25 Tree 0 0 0 Total 200 350 500 Figure 9. Plant community growth curve (percent production by month). TX4006 , Shortgrass Shrub Dominant Community. Shortgrasses with 40% woody canopy of shrubs..
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 State 2
EncroachedThe Encroached state is characterized by a reduction in warm-season grass diversity, loss of herbaceous cover and increased bare ground. Native shrubs have increased in cover and density and are controlling site resources, including infiltration, runoff, and nutrient cycling.
Dominant plant species
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creosote bush (Larrea tridentata), shrub
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Chino grama (Bouteloua ramosa), grass
Community 2.1
Shrub/Midgrass/ShortgrassThis plant community is the result of improper grazing (high stocking rates). Extended drought exacerbates the transition from the reference. A compositional and irreversible threshold has been crossed. The vast majority of the most palatable grasses, forbs, and sub-shrubs have been eradicated from the plant community. Although palatable when green, Chino grama increases following the decrease of other midgrasses. It becomes the dominant, and in some places, the only perennial bunchgrass observed. Fluffgrass is an unpalatable shortgrass that increases following disturbance. Some perennial forbs and succulents increase such as dogweed, coldenia, pricklypear, and lechuguilla. Because of the inherently low productivity of the site, shrub encroachment following perennial grass reduction is very slow if at all.
Percentage of total plant community by weight is estimated to be 25 percent grass, 60 percent shrubs, and 15 percent forbs.
Resilience management. Climate, soil temperatures and properties, are some of the major factors limiting the restoration of the reference. Continued overgrazing will transition this plant community to a Shrubland/Annual Grasses community (2.2). Prescribed grazing will help maintain the ecologic integrity of the community. Stocking rates need to be flexible and adjusted to carrying capacity because of sporadic rainfall.
Community 2.2
Shrub/Annual GrassesPlant community 2.2 is the result of excessive overutilization of plant resources. Annual and shortgrasses dominated the herbaceous layer. Few isolated Chino grama plants can be observed. Succulents and unpalatable perennial forbs increase. Because of the inherently low productivity of the site, shrub encroachment following perennial grass reduction is very slow if at all. The appearance of this community is a very sparse shrubland. Shrubs are scattered and not overlapping. Overall canopy cover is low.
Percentage of total plant community by weight is estimated to be 5 percent grass, 80 percent shrubs, and 15 percent forbs.
Resilience management. With several years of prescribed grazing and favorable rainfall, some areas of this plant community have the potential to return to a Shrub mid/shortgrass community (2.1). Some areas within the lowest elevations of the site’s range, may not be able to transition back to community 2.1.
Pathway 2.1A
Community 2.1 to 2.2This plant community shift is the result of improper grazing (high stocking rates). Extended drought exacerbates the transition from the reference.
Pathway 2.2A
Community 2.2 to 2.1With a prescribed grazing plan that includes rest and recovery periods along with favorable rainfall, the site may shift back to community 2.1.
Transition T1A
State 1 to 2This transition is the result of improper grazing (high stocking rates). Extended drought exacerbates the transition from the reference.
Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Mid/Shortgrasses 100–250 Chino grama BORA4 Bouteloua ramosa 60–150 – bush muhly MUPO2 Muhlenbergia porteri 20–50 – black grama BOER4 Bouteloua eriopoda 20–50 – 2 Mid/Shortgrasses 30–75 threeawn ARIST Aristida 10–25 – fall witchgrass DICO6 Digitaria cognata 10–25 – slim tridens TRMU Tridens muticus 10–25 – sideoats grama BOCU Bouteloua curtipendula 0–5 – Arizona cottontop DICA8 Digitaria californica 0–5 – 3 Shortgrasses 10–25 nineawn pappusgrass ENDE Enneapogon desvauxii 4–10 – hairy woollygrass ERPI5 Erioneuron pilosum 2–5 – red grama BOTR2 Bouteloua trifida 2–5 – low woollygrass DAPU7 Dasyochloa pulchella 2–5 – Shrub/Vine4 Shrubs 40–100 creosote bush LATR2 Larrea tridentata 20–50 – Texas barometer bush LEFR3 Leucophyllum frutescens 4–10 – mariola PAIN2 Parthenium incanum 4–10 – resinbush VIST Viguiera stenoloba 4–10 – Texas lignum-vitae GUAN Guaiacum angustifolium 4–10 – Grass, annual 2GA Grass, annual 0–6 – whitethorn acacia ACCO2 Acacia constricta 2–5 – jointfir EPHED Ephedra 2–5 – ocotillo FOSP2 Fouquieria splendens 2–5 – littleleaf ratany KRER Krameria erecta 2–5 – 5 Fibrous/Succulents 10–25 lechuguilla AGLE Agave lechuguilla 2–5 – Christmas cactus CYLE8 Cylindropuntia leptocaulis 2–5 – Texas sotol DATE3 Dasylirion texanum 2–5 – candelilla EUAN3 Euphorbia antisyphilitica 2–5 – leatherstem JADI Jatropha dioica 0–5 – pricklypear OPUNT Opuntia 2–5 – yucca YUCCA Yucca 2–5 – Forb6 Perennial 10–20 woody crinklemat TICAC Tiquilia canescens var. canescens 4–10 – featherplume DAFO Dalea formosa 2–5 – littleleaf ratany KRER Krameria erecta 2–5 – Forb, perennial 2FP Forb, perennial 1–3 – croton CROTO Croton 1–3 – lacy tansyaster MAPI Machaeranthera pinnatifida 1–3 – menodora MENOD Menodora 1–3 – woolly paperflower PSTA Psilostrophe tagetina 1–3 – globemallow SPHAE Sphaeralcea 1–3 – pricklyleaf dogweed THAC Thymophylla acerosa 1–3 – woody crinklemat TICAC Tiquilia canescens var. canescens 1–3 – vervain VERBE Verbena 1–3 – 7 Annual 0–5 Forb, annual 2FA Forb, annual 0–3 – bladderpod LESQU Lesquerella 0–2 – Table 7. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 8. Community 2.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
The historic Midgrass/Shrub Community (1.1) was part of the habitat for mule deer, songbirds, birds of prey, small mammals, and predators such as coyote, bobcat, and mountain lion. As the site changes through the Midgrass/Shrub Community (1.1) toward the Creosotebush Shrubland Community (2.1), it becomes less suitable to many animal species due to the increase in bare ground and erosion and subsequent lack of food and cover.
Many species of wildlife utilize this site for at least a portion of their habitat needs. It is also important to balance wildlife populations with carrying capacity. Mule deer need high protein forbs and browse. They generally eat a wide variety of browse and forbs and small amounts of grass. Quail and dove prefer a combination of low shrubs, bunch grass, bare ground, and forbs. Game bird species such as mourning and white wing dove and scaled quail can be present on the site. Smaller mammals present include rodents, jackrabbits, cottontail rabbits, raccoons, and skunks. Mammalian predators like coyote, bobcat, and mountain lion can potentially be found at the site. Numerous species of snakes and lizards are native to the site.
Non-game species of birds found on this site include songbirds and birds of prey. Habitat on this site that provides a large diversity of grasses, forbs, and shrubs will support a variety and abundance of songbirds. Birds of prey are important to keep the numbers of rodents, rabbits, and snakes in balance.
Cattle find the best forage in the Midgrasses/Shrub Community (1.1). As this site reaches the Creosotebush Shrubland Community (2.1), it becomes difficult to find enough forage to thrive. An assessment of vegetation is needed to determine the site’s current carrying capacity in order to avoid overgrazing. Carrying capacity in the Trans-Pecos will vary greatly from year to year depending on the episodic precipitation.
Plant Preference by Animal:
These preferences are somewhat general in nature as the preference for a plant is dependent upon animals grazing experience, time of year, availability of choices, and total forage supply.
Hydrological functions
The Gravelly 8-14" PZ site is a well-drained, very shallow to very deep gravelly upland. Its soils are moderately slow to moderately rapidly permeable. Under historic climax condition the vegetation intercepted and utilized much of the incoming rainfall. There was runoff during torrential rains due to the limited water holding capacity of the soil. The presence of rocks enhances the effectiveness of rainfall, especially small rainfall events, by concentrating it on a smaller surface area. When the site changes from grassland to shrub community there is a structural change resulting in faster runoff that carries soil particles away. Less of the rainfall is intercepted and infiltrates into the soil.
Recreational uses
The Gravelly 8-14" PZ site is suited for many outdoor recreational uses including hunting, hiking, and bird watching. Its rugged beauty and topography make it a unique site and colorful forbs can be found on or near the site throughout the spring and summer.
Supporting information
Other references
1. Archer S. 1994. Woody plant encroachment into southwestern shrubs and savannas: rates, patterns and proximate causes. In Ecological implications of livestock Herbivory in the West, Ed M Vavra, W Laycock, R Pieper, pp13-68, Denver, CO: society for Range Management
2. Brewer, Clay E., Harveson, Louis A. 2005. Diets of Bighorn Sheep in the Chihuahuan Desert, Texas.
3. Briske, D. D. 2008. Etal. Rotational Grazing on Rangelands: Reconciliation of Perception and Experimental Evidence. Rangeland Ecol. Management 613-17, January.
4. Downie, A. E. 1978. Terrell County, Texas, its past- its people. San Angelo, Texas: Rangle Printing.
5. Gould F. 1978. Common Texas Grasses: an illustrated guide. College Station, Texas: Texas A & M Press.
Hardy, Jean Evans. 1997. Flora and Vegetation of the Solitario Dome, Brewster and Presidio Counties, Texas. A Thesis Presented to the Graduate Council Sul Ross State University.
6. Hart, Charles R. et al. 2003. Toxic Plants of Texas. Texas Cooperative Extension. Texas A&M University System.
7. Heischmidt RK, Stuth, Eds. 1991 Grazing Management: an ecological perspective. Portland, Oregon: Timberline Press
Keller, David W. 2005. Below The Escondido Rim: A History of the O2 Ranch in the Texas Big Bend. Alpine, Texas: Center for Big Bend Studies, Sul Ross State University.
8. Langford, JO. 1952. Big Bend: A Homesteader’s Story. Austin, Texas: University of Texas Press.
9. MacLeod, William. 2003. Big Bend Vistas: a geological exploration. Austin, Texas: Capital Printing Company.
10. McPherson, Guy R. 1995. The Desert Shrub. Chapter 5: The Role of Fire in the Desert Shrubs. Tucson, Arizona. The University of Arizona Press.
11. Powell, A. Michael. 1998. Trees and Shrubs of the Trans-Pecos and Adjacent Areas. Austin, Texas: University of Texas Press.
12. Thomas, Jack W and D Toweill. 1982. Elk of North America. Mechanicsburg, Pennsylvania: Stackpole Books.
13. Tyler, Ron C. 1996. The Big Bend: a history of the last Texas frontier. College Station, Texas: Texas A&M University Press.
14. USDA/NRCS Soil Survey Manuals for Jeff Davis, Pecos, and Reeves Counties
Van Devender, Thomas R. 1995. The Desert Shrub. Chapter 3: Desert Shrub History. Tucson, Arizona: The University of Arizona Press.
15. Warnock, Barton. 1977. Wildflowers of the Davis Mountains and the Marathon Basin. Alpine, Texas: Sul Ross State University.
16. Wauer, Roland H. 1973. Naturalist’s Big Bend. Santa Fe, New Mexico: Peregrine Productions.
17. Weniger, D. 1984. The Explorer’s Texas: The Lands and Waters, Vol 1. Austin, Texas: Eakin PressContributors
Michael Margo, RMS, NRCS, Marfa, Texas
Technical Staff, NRCS, Pecos, Texas
Travis Waiser, MLRA Leader, NRCS, Kerrville, TXApproval
Bryan Christensen, 9/19/2023
Acknowledgments
Site Development and Testing Plan: Future work, as described in a Project Plan, to validate the information in this Provisional Ecological Site Description is needed. This will include field activities to collect low, medium and high intensity sampling, soil correlations, and analysis of that data. Annual field reviews should be done by soil scientists and vegetation specialists. A final field review, peer review, quality control, and quality assurance reviews of the ESD will be needed to produce the final document. Annual reviews of the Project Plan are to be conducted by the Ecological Site Technical Team. The following individuals assisted with the development of this site description: Mr. Charles Anderson –Rangeland Management Specialist- NRCS; San Angelo, Texas Dr. Louis Harveson – Department Chair Department of Natural Resource Management, Sul Ross State University Mr. Preston Irwin – Rangeland Management Specialist-NRCS; Fort Stockton, Texas Dr. Lynn Loomis - Soil Scientist-NRCS; Marfa, Texas Mr. Rusty Dowell, Resource Soil Scientist, NRCS, San Angelo, Texas Mr. Justin Clary – Rangeland Management Specialist – NRCS; Temple, Texas Dr. AM Powell, Professor Emeritus – Sul Ross State University QC/QA completed by: Bryan Christensen, SRESS, NRCS, Temple, TX Erin Hourihan, ESDQS, NRCS, Temple, TX
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) Michael Margo, RMS, NRCS, Marfa, TX Contact for lead author Zone RMS, San Angelo, TX 325-944-0147 Date 12/05/2011 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
None -
Presence of water flow patterns:
None, except following high intesity storms, when short (less than 1 m) and discontinuous flow patterns may appear. Flow patterns in drainages are linear and continuous. -
Number and height of erosional pedestals or terracettes:
None -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
2-5% bare ground -
Number of gullies and erosion associated with gullies:
None -
Extent of wind scoured, blowouts and/or depositional areas:
None -
Amount of litter movement (describe size and distance expected to travel):
In drainages, there can be significant amounts of litter moved long distances. On most of the site, minimal and short distance (<5ft) of litter movement associated with high intense rainfall. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil stability values usually ranging from 4-6 under vegetation and 2-3 in the interspaces -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
1-2 inches thick, pale brown surface horizon with a moderate medium granular structure. Data from Stillwell soil series description -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
A high canopy cover of midgrass bunch and stoliniferous grasses will help minimize runoff and maximize infiltration. Grasses should comprise approximately 60% of total plant compostion by weight. Shrubs will comprise about 30% by weight. -
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
None -
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:
Mid bunchgrass (Chino grama)Sub-dominant:
mid stoloniferous grasses > mid/tall shrubsOther:
Subshrubs = fibrous/succulents > perennial forbs > annual forbs and grassesAdditional:
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Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
All grasses will show some mortality and decadence in addition to annual forbs. Mid/tall perennial shrubs will show some mortality or decadence only after prolonged and severe droughts. Subshrubs will be less resistant to severe droughts than mid/tall perennial shrubs. -
Average percent litter cover (%) and depth ( in):
-
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
200-500 lbs/ac -
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:
Dry climate prevents non-native species to encroach on this site. Creosotebush will increase some but will still remain in a widely spaced pattern that is characteristic of desert climates. -
Perennial plant reproductive capability:
All species should be capable of reproducing.
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