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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
R035XE513AZ Sandy Loam Terrace 6-10" p.z.
Sandy Loam Terrace 610" pz Occasionally found in the larger interdune areas if the eolian sand is not present.
Table 1. Dominant plant species
Tree Not specified
Shrub Not specified
Herbaceous Not specified
Physiographic features
This site occurs primarily on eolian dunes ad interdunes. The depth of eolian deposit can vary considerably. Soil depth ranges from shallow to deep. This site can have a significant amount of warm and cool season perennial grasses, and the deeper sands support more grasses than when the sand is shallow. Various cactus species may also be plentiful. Ocassionally, the deepest-rooted species, such as mesquite and catclaw, may benefit from a fluctuating water table.
Table 2. Representative physiographic features
Landforms (1) Dune
(2) Interdune
Elevation 1600 – 4600 ft Slope 1 – 15 % Water table depth 60 – 72 in 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
Soil textures on this site range from fine sand to loamy fine sand with few gravels and cobbles, except where the eolian deposits are thin and the underlying material has been exposed. They are slightly to strongly effervescent on the surface. Soil pH range is 7.9-8 (moderately alkaline).
Typical taxonomic unit on this site includes:
SSA-701 Grand Canyon Area MU 145 Typic torripsamments.Table 4. Representative soil features
Surface texture (1) Fine sand
(2) Loamy fine sand
Family particle size (1) Sandy
Drainage class Well drained to excessively drained Permeability class Rapid Soil depth 20 – 60 in Surface fragment cover <=3" 0 – 5 % Available water capacity
(0-40in)0 – 2.5 in Calcium carbonate equivalent
(0-40in)2 – 15 % Electrical conductivity
(0-40in)0 – 2 mmhos/cm Soil reaction (1:1 water)
(0-40in)7.8 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)0 – 5 % 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 community has a significant component of warm and cool season grasses, especially in areas where the sand is deepest. Cacti are common, usually various Opuntias. Fourwing saltbush and Ephedras are well represented, with occasional thickets of mesquite and catclaw.
Figure 3. 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 170 – 245 Shrub/Vine 55 – 110 Forb 20 – 75 Total 245 – 430 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 5–110 big galleta PLRI3 Pleuraphis rigida 20–55 – spike dropseed SPCO4 Sporobolus contractus 20–55 – sand dropseed SPCR Sporobolus cryptandrus 20–55 – mesa dropseed SPFL2 Sporobolus flexuosus 20–55 – 2 0–10 Grass, perennial 2GP Grass, perennial 0–4 – sand bluestem ANHA Andropogon hallii 0–4 – cane bluestem BOBA3 Bothriochloa barbinodis 0–4 – vine mesquite PAOB Panicum obtusum 0–4 – 3 0–5 Grass, perennial 2GP Grass, perennial 0–3 – red grama BOTR2 Bouteloua trifida 0–3 – low woollygrass DAPU7 Dasyochloa pulchella 0–3 – 4 55–110 Indian ricegrass ACHY Achnatherum hymenoides 40–75 – purple threeawn ARPU9 Aristida purpurea 20–40 – blue threeawn ARPUN Aristida purpurea var. nealleyi 20–40 – 5 0–20 Grass, annual 2GA Grass, annual 5–10 – sixweeks grama BOBA2 Bouteloua barbata 5–10 – sixweeks fescue VUOC Vulpia octoflora 5–10 – 6 0–10 Forb, perennial 2FP Forb, perennial 0–4 – desert trumpet ERIN4 Eriogonum inflatum 0–4 – pepperweed LEPID Lepidium 0–4 – globemallow SPHAE Sphaeralcea 0–4 – Forb7 10–30 Forb, perennial 2FP Forb, perennial 0–10 – fragrant white sand verbena ABEL Abronia elliptica 0–10 – trailing windmills ALIN Allionia incarnata 0–10 – tansyaster MACHA Machaeranthera 0–10 – brownplume wirelettuce STPA4 Stephanomeria pauciflora 0–10 – 8 0–40 Forb, annual 2FA Forb, annual 0–20 – milkvetch ASTRA Astragalus 0–20 – buckwheat ERIOG Eriogonum 0–20 – desertdandelion MALAC3 Malacothrix 0–20 – birdcage evening primrose OEDE2 Oenothera deltoides 0–20 – desert Indianwheat PLOV Plantago ovata 0–20 – Shrub/Vine9 0–10 Shrub, other 2S Shrub, other 0–2 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–2 – alkali goldenbush ISAC2 Isocoma acradenia 0–2 – mountain phlox PHAU3 Phlox austromontana 0–2 – slender poreleaf POGR5 Porophyllum gracile 0–2 – pricklyleaf dogweed THAC Thymophylla acerosa 0–2 – Mojave woodyaster XYTO2 Xylorhiza tortifolia 0–2 – 10 5–40 catclaw acacia ACGR Acacia greggii 5–20 – honey mesquite PRGL2 Prosopis glandulosa 5–20 – 11 20–40 fourwing saltbush ATCA2 Atriplex canescens 10–25 – jointfir EPHED Ephedra 5–20 – 12 0–10 Shrub, other 2S Shrub, other 0–5 – burrobush AMDU2 Ambrosia dumosa 0–5 – shortleaf baccharis BABR Baccharis brachyphylla 0–5 – sweetbush BEJU Bebbia juncea 0–5 – brittlebush ENFA Encelia farinosa 0–5 – rubber rabbitbrush ERNA10 Ericameria nauseosa 0–5 – skunkbush sumac RHTR Rhus trilobata 0–5 – Mojave seablite SUMO Suaeda moquinii 0–5 – 13 5–40 Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 0–5 – cactus apple OPEN3 Opuntia engelmannii 5–2 – twistspine pricklypear OPMA2 Opuntia macrorhiza 5–2 – plains pricklypear OPPO Opuntia polyacantha 5–2 – 14 0–5 Utah agave AGUT Agave utahensis 0–3 – soaptree yucca YUEL Yucca elata 0–3 – Interpretations
Supporting information
Type locality
Location 1: Coconino County, AZ Latitude 36° 22′ 25″ Longitude 112° 28′ 14″ General legal description In the interior of the Grand Canyon; 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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