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Draft. A draft ecological site description is either incomplete or has not undergone quality control and quality assurance review.
MLRA notes
Major Land Resource Area (MLRA): 035X–Colorado Plateau
AZ CRA 35.5 – Grand Canyon Corridor
Elevations range from 1600 to 4500 feet and precipitation averages 6 to 10 inches per year. Extreme elevation and aspect changes make this area unique. Vegetation includes Mormon tea, catclaw, white brittlebush, blackbrush, prickly pear, cholla species, big galleta, and blue threeawn. The soil temperature regime ranges from thermic to mesic and the soil moisture regime is typic aridic. This unit occurs within the Colorado Plateau Physiographic Province and is characterized by extreme vertical escarpments and strong aspect differences over short distances. Sedimentary rock classes dominate the Grand Canyon and exposures consist of a thick sequence of relatively undeformed formations.Associated sites
R035XE507AZ Limy Slopes 6-10" p.z.
Limy Slops 6-10" pz Soils that have not developed a petriocalcic horizon or are deeper.
Similar sites
R035XE519AZ Limy Upland 6-10" p.z. Shallow
Limy Upland 6-10" pz shallow A similar plant community found on flatter slopes, fans and plateaus.
Table 1. Dominant plant species
Tree Not specified
Shrub Not specified
Herbaceous Not specified
Physiographic features
This site is found on steep colluvial sideslopes and fan terraces of plateau escarpments and canyon sidewalls. Soil textures are sandy loam to loam, are very stony or cobbly, and are shallow and very shallow to a petrocalcic horizon The soil is slightlyto violently effervescent at the surface. The site is found on all aspects.
Table 2. Representative physiographic features
Landforms (1) Terrace
(2) Escarpment
(3) Pediment
Elevation 1600 – 4600 ft Slope 15 – 60 % Aspect Aspect is not a significant factor Climatic features
The climate of the land resource unit is arid to semiarid with warm summers and cool winters. The mean annual precipitation ranges from 6 – 10 inches, but it is very erratic, often varying substantially from year to year. The majority of the precipitation falls during the between October through May. This precipitation comes as gentile rain or occasionally snow from frontal storms coming out to the Pacific Ocean. Snow is infrequent and rarely last more than 1-2 days. The remaining precipitation comes from July through September as spotty, unreliable and sometimes violent thunderstorms. The moisture for this precipitation originates in the Gulf of Mexico (and the Pacific Ocean in the fall) and flows into the area on the north end of the Mexican monsoon. Late May through late June is generally a dry period. The mean annual air temperature ranges from 55 to 69 degrees Fahrenheit (F). The frost-free period (air temperature > 32 degrees F) ranges from 180 to 220 days (@ 50 percent probability).
Table 3 Representative climatic features
Frost-free period (average) 200 days Freeze-free period (average) 220 days Precipitation total (average) 10 in BarLineFigure 1. Monthly precipitation range
BarLineFigure 2. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
Soils on this site have a sandy loam to loam surface texture and are very to extremely gravelly, stony, cobbly, and/or channery. The soil surface is sightly t violently effervescent; however, the subsoil increases substantially in lime content and ends at a pertocalcic horizon. Soils are moderately alkaline (pH range 7.9-8.4), and are non-sodic, non-saline.
Typical taxonomic units on this site include:
SSA-701 Grand Canyon Area MU's 16 & 17 Calcic Petrocalcids, 32 Curob (family), 159 Seeg (family) and Valleycity (family), 142 typic petrocalcids, and 164 Winkel (family).Table 4. Representative soil features
Parent material (1) Alluvium – limestone and sandstone
(2) Colluvium – shale
Surface texture (1) Extremely gravelly loam
(2) Very stony sandy loam
(3) Extremely channery
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderate to moderately rapid Soil depth 9 – 20 in Surface fragment cover <=3" 0 – 20 % Surface fragment cover >3" 0 – 35 % Available water capacity
(0-40in)0 – 5 in Calcium carbonate equivalent
(0-40in)Not specified Electrical conductivity
(0-40in)0 – 2 mmhos/cm Sodium adsorption ratio
(0-40in)0 – 2 Soil reaction (1:1 water)
(0-40in)7.8 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)0 – 20 % Subsurface fragment volume >3"
(Depth not specified)0 – 40 % Ecological dynamics
The historic climax plant community (HCPC) for a site in North America is the plant community that existed at the time of European immigration and settlement. It is the plant community that was best adapted to the unique combination of environmental factors associated with the site at that time. The HCPC was in dynamic equilibrium with its environment and was able to avoid displacement by the suite of disturbances and disturbance patterns (magnitude and frequency) that naturally occurred within the area occupied by the site. Natural disturbances, such as drought, fire, grazing of native fauna, and insects, were inherent in the development and maintenance of the plant community. The effects of these disturbances are part of the range of characteristics of the site that contribute to the dynamic equilibrium. Fluctuations in the plant community’s structure and function caused by the effects of these natural disturbances establish the boundaries of dynamic equilibrium. They are accounted for as part of the range of characteristics for the ecological site. The HCPC is not a precise assemblage of species for which the proportions are the same from place to place or from year to year. Variability is apparent in productivity and occurrence of individual species.
The HCPC for this ecological site has been estimated by sampling relict or relatively undisturbed sites and/or reviewing historic records.
A plant community that is subjected to abnormal disturbances and physical site deterioration or that is protected from natural influences, such as fire and grazing, for long periods seldom typifies the HCPC. Any physical site deterioration caused by the abnormal disturbance may result in the crossing of a threshold or irreversible boundary to another state, or equilibrium, for the ecological site. There may be multiple thresholds and states possible for an ecological site, determined by the type and or severity of abnormal disturbance. The known states and transition pathways for this ecological site are described in the accompanying state and transition model.
The “Plant Community Plant Species Composition” table provides a list of species and each species or group of species’ annual production in pounds per acre (air-dry weight) expected in a normal rainfall year. Low and high production yields represent the modal range of variability for that species or group of species across the extent of the ecological site.
The “Annual Production by Plant Type” table provides the median air-dry production and the fluctuations to be expected during favorable, normal, and unfavorable years.
The present plant community on an ecological site can be compared to the various common vegetation states that can exist on the site. The degree of similarity is expressed through a similarity index. To determine the similarity index, compare the production of each species to that shown in the plant community description. For each species, count no more than the maximum amount shown for the species, and for each group, count no more than the maximum shown for the group. Divide the resulting total by the total representative value shown in the “Annual Production by Plant Type” table for the reference plant community. Variations in production due to above or below normal rainfall, incomplete growing season or utilization must be corrected before comparing it to the site description. The “Worksheet for Determining Similarity Index” is useful in making these corrections. The accompanying growth curve can be used as a guide for estimating percent of growth completed.
State and transition model
Custom diagramStandard diagram
More interactive model formats are also available. View Interactive Models
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 1
Historic Climax Plant CommunityCommunity 1.1
Historic Climax Plant CommunityThis plant communiy is dominated by blackbrush. Other shrubs are scattered across the site in small amounts, notably Ephedras. There are small amounts of cool and warm season perennial grasses.
Figure 3. Annual production by plant type (representative values) or group (midpoint values)
Additional community tables
Table 5. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 15–40 Indian ricegrass ACHY Achnatherum hymenoides 5–15 – desert needlegrass ACSP12 Achnatherum speciosum 5–15 – needle and thread HECOC8 Hesperostipa comata ssp. comata 5–15 – slim tridens TRMU Tridens muticus 5–15 – 2 15–40 black grama BOER4 Bouteloua eriopoda 5–15 – bush muhly MUPO2 Muhlenbergia porteri 5–15 – sand dropseed SPCR Sporobolus cryptandrus 5–15 – James' galleta PLJA Pleuraphis jamesii 5–10 – big galleta PLRI3 Pleuraphis rigida 5–10 – 3 5–15 Grass, annual 2GA Grass, annual 2–7 – sixweeks grama BOBA2 Bouteloua barbata 2–7 – sixweeks fescue VUOC Vulpia octoflora 2–7 – Forb4 0–10 desert trumpet ERIN4 Eriogonum inflatum 2–4 – globemallow SPHAE Sphaeralcea 2–4 – Forb, perennial 2FP Forb, perennial 1–4 – winding mariposa lily CAFL Calochortus flexuosus 1–4 – desert trumpet ERIN4 Eriogonum inflatum 1–4 – globemallow SPHAE Sphaeralcea 1–4 – 5 0–10 Forb, perennial 2FP Forb, perennial 0–5 – Colorado four o'clock MIMU Mirabilis multiflora 0–5 – 6 0–1 Forb, annual 2FA Forb, annual 0–15 – Shrub/Vine7 5–15 Shrub, other 2S Shrub, other 0–5 – dyssodia DYSSO Dyssodia 0–5 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–5 – whitestem paperflower PSCO2 Psilostrophe cooperi 0–5 – Parish's goldeneye VIPA14 Viguiera parishii 0–5 – 8 165–220 blackbrush CORA Coleogyne ramosissima 140–195 – Nevada jointfir EPNE Ephedra nevadensis 15–40 – 9 5–15 Shrub, other 2S Shrub, other 0–5 – catclaw acacia ACGR Acacia greggii 0–5 – fourwing saltbush ATCA2 Atriplex canescens 0–5 – winterfat KRLA2 Krascheninnikovia lanata 0–5 – desert-thorn LYCIU Lycium 0–5 – mariola PAIN2 Parthenium incanum 0–5 – 10 0–10 plains pricklypear OPPO Opuntia polyacantha 0–5 – 11 0–10 Utah agave AGUT Agave utahensis 0–5 – banana yucca YUBA Yucca baccata 0–5 – Interpretations
Supporting information
Type locality
Location 1: Mohave County, AZ Latitude 36° 5′ 19″ Longitude 112° 7′ 47″ General legal description On the Tonto Platform; 1,300 feet southwest of Plateau Point Contributors
Larry D. Ellicott
Steve BarkerRangeland 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 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
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Presence of water flow patterns:
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Number and height of erosional pedestals or terracettes:
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Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
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Number of gullies and erosion associated with gullies:
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Extent of wind scoured, blowouts and/or depositional areas:
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Amount of litter movement (describe size and distance expected to travel):
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Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
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Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
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Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
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Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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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:
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Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
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Average percent litter cover (%) and depth ( in):
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Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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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:
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Perennial plant reproductive capability:
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PrintThe Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.
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