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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.
MLRA notes
Major Land Resource Area (MLRA): 040X–Sonoran Basin and Range
AZ 40.3 – Colorado Sonoran Desert
Elevations range from 300 to 1200 feet and precipitation averages 3 to 7 inches per year. Vegetation includes creosotebush, white bursage, brittlebush, Mormon tea, teddybear cholla, elephant tree, smoke tree, ocotillo, and big galleta. The soil temperature regime is hyperthermic and the soil moisture regime is typic aridic. This unit occurs within the Basin and Range Physiographic Province and is characterized by numerous mountain ranges that rise abruptly from broad, plain-like valleys and basins. Igneous and metamorphic rock classes dominate the mountain ranges and sediments filling the basins represent combinations of fluvial, lacustrine, colluvial and alluvial deposits.Table 1. Dominant plant species
Tree (1) Parkinsonia microphylla
Shrub (1) Ambrosia dumosa
(2) Larrea tridentata var. tridentataHerbaceous (1) Pleuraphis rigida
(2) Muhlenbergia porteriPhysiographic features
This site occurs as nearly level to gently sloping fan terraces.
Table 2. Representative physiographic features
Landforms (1) Terrace
(2) Fan
Elevation 75 – 1000 ft Slope 1 – 3 % Climatic features
Precipitation in this common resource area ranges from 3-7 inches yearly. Despite historical averages in rainfall amounts, as one moves from east to west in this resource area rains become more unpredictable and variable with Coefficients of Variation of annual rainfall equal to 44% at Gila Bend and 65% at Mohawk. Winter-Summer rainfall ratios are 40-60%. Summer rains fall July-September, originate in the Gulf of Mexico and are convective, usually brief intense thunderstorms. Summer thunderstorms usually form over the mountains in the afternoon and spread to the valleys and plains in the evening. The intensity of this precipitation is moderate to heavy, but rarely lasts more than half an hour. Many times these storms produce little more than gusty winds and light showers. Cool season moisture tends to be frontal, originate in the Pacific and Gulf of California and falls in widespread storms with long duration and low intensity. Snow is very rare and falls normally only in the higher mountains.
Mean temperatures for the hottest month (Jul) is 93 F; the coldest month (Jan) is 53 F. Extreme temperatures of 125 F and 10 F have been recorded. Long periods with little or no effective moisture occur frequently.
The winter-spring precipitation is the most dependable on the site. Perennial grasses, though classed as warm season growers, grow actively year-round when moisture is available. Shrubs and trees generally respond to seasonal moisture. The two rainy periods bring about their respective production of either winter or summer annual grasses and forbs.Table 3 Representative climatic features
Frost-free period (average) 360 days Freeze-free period (average) 0 days Precipitation total (average) 10 in BarLineFigure 1. Monthly precipitation range
BarLineFigure 2. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
These are deep soils. They are calcareous throughout. They may either be sandy throughout, or coarse loamy with a surface cap of sand or loamy sand. Plant soil-moisture relationships are fair.
Soils mapped on this site include: in SSA-627 Southern Mohave county MU Superstition-108; SSA-649 Yuma-Wellton area MU's Superstition-28, Wellton-33 & 34, Dateland-34; SSA-653 Gila Bend-Ajo area MU's Coolidge LFS-11 & Denure LFS-57; SSA-656 Colorado River Indian Reservation MU Superstition-28 & 29.Table 4. Representative soil features
Surface texture (1) Sand
(2) Loam
(3) Loamy fine sand
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately rapid to very rapid Soil depth 60 in Surface fragment cover <=3" 0 – 3 % Surface fragment cover >3" Not specified Available water capacity
(0-40in)4.2 – 7.2 in Calcium carbonate equivalent
(0-40in)3 – 10 % Electrical conductivity
(0-40in)0 – 4 mmhos/cm Sodium adsorption ratio
(0-40in)Not specified Soil reaction (1:1 water)
(0-40in)7.9 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)0 – 10 % Subsurface fragment volume >3"
(Depth not specified)Not specified Ecological dynamics
The plant communities found on an ecological site are naturally variable. Composition and production will vary with yearly conditions, location, aspect, and the natural variability of the soils. The Historical Climax Plant Community represents the natural potential plant communities found on relict or relatively undisturbed sites. Other plant communities described here represent plant communities that are known to occur when the site is disturbed by factors such as fire, grazing, or drought.
Production data provided in this site description is standardized to air dry weight at the end of the summer growing season. The plant communities described in this site description are based on near normal rainfall years.
NRCS uses a Similarity Index to compare existing plant communities to the plant communities described here. Similarity index is determined by comparing the production and composition of a plant community to the production and composition of a plant community described in this site description. To determine Similarity index, compare the production (air dry weight) 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 amount shown for each group. Divide the resulting total by the total normal year production shown in the plant community description. If the rainfall has been significantly above or below normal, use the total production shown for above or below normal years. If field data is not collected at the end of the summer growing season, then the field data must be corrected to the end of the year production before comparing it to the site description. The growth curve can be used as a guide for estimating production at the end of the summer growing season.
State and transition model
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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 CommunityThe potential plant community is a mixture of desert shrubs with an understory of perennial grasses and forbs. Winter and summer annual grasses and forbs are abundant in years with above-average moisture in their respective seasons.
Continued grazing during the various growing seasons results in a decline in perennial grasses and an increase in creosotebush. The sandy surface of these soils is subject to severe wind erosion as the perennial plant cover is depleted.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)Shrub/Vine 250 288 325 Grass/Grasslike 150 175 200 Forb 25 37 50 Tree 5 10 15 Total 430 510 590 Figure 4. Plant community growth curve (percent production by month). AZ4041 , 40.3 3-7" p.z. all sites. Most growth occurs in the winter to early spring, plants are dormant May through October..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 5 20 40 25 0 0 0 0 0 0 5 5 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 Dominant Grass 125–150 big galleta PLRI3 Pleuraphis rigida 125–150 – 2 Misc. Perennial Grasses 15–25 bush muhly MUPO2 Muhlenbergia porteri 5–10 – sand dropseed SPCR Sporobolus cryptandrus 2–5 – California threeawn ARCA9 Aristida californica 2–5 – threeawn ARIST Aristida 2–5 – 3 Annual Grasses 5–25 sixweeks fescue VUOC Vulpia octoflora 0–10 – littleseed muhly MUMI Muhlenbergia microsperma 0–5 – Bigelow's bluegrass POBI Poa bigelovii 0–3 – sixweeks threeawn ARAD Aristida adscensionis 0–3 – needle grama BOAR Bouteloua aristidoides 0–3 – sixweeks grama BOBA2 Bouteloua barbata 0–3 – low woollygrass DAPU7 Dasyochloa pulchella 0–1 – Forb4 Misc. Forbs 25–50 Texas pipewort ERTE8 Eriocaulon texense 1–5 – Thomas' buckwheat ERTH Eriogonum thomasii 0–1 – spurge EUPHO Euphorbia 0–1 – hairy desertsunflower GECA2 Geraea canescens 0–1 – desert lily HEUN2 Hesperocallis undulata 0–1 – Arizona poppy KAGR Kallstroemia grandiflora 0–1 – Gordon's bladderpod LEGO Lesquerella gordonii 0–1 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 0–1 – Bigelow's linanthus LIBI2 Linanthus bigelovii 0–1 – foothill deervetch LOHU2 Lotus humistratus 0–1 – strigose bird's-foot trefoil LOSTT Lotus strigosus var. tomentellus 0–1 – Coulter's lupine LUSP2 Lupinus sparsiflorus 0–1 – California desertdandelion MACA6 Malacothrix californica 0–1 – blazingstar MENTZ Mentzelia 0–1 – bristly nama NAHI Nama hispidum 0–1 – glandular threadplant NEGL Nemacladus glanduliferus 0–1 – evening primrose OENOT Oenothera 0–1 – desert evening primrose OEPR Oenothera primiveris 0–1 – lineleaf whitepuff OLLI Oligomeris linifolia 0–1 – combseed PECTO Pectocarya 0–1 – manybristle chinchweed PEPA2 Pectis papposa 0–1 – phacelia PHACE Phacelia 0–1 – desert Indianwheat PLOV Plantago ovata 0–1 – desert unicorn-plant PRAL4 Proboscidea althaeifolia 0–1 – New Mexico plumeseed RANE Rafinesquia neomexicana 0–1 – desert globemallow SPAM2 Sphaeralcea ambigua 0–1 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 0–1 – small wirelettuce STEX Stephanomeria exigua 0–1 – longbeak streptanthella STLO4 Streptanthella longirostris 0–1 – woolly tidestromia TILA2 Tidestromia lanuginosa 0–1 – carelessweed AMPA Amaranthus palmeri 0–1 – bristly fiddleneck AMTE3 Amsinckia tessellata 0–1 – New Mexico silverbush ARNE2 Argythamnia neomexicana 0–1 – milkvetch ASTRA Astragalus 0–1 – desert marigold BAMU Baileya multiradiata 0–1 – Spanish needles BIBI7 Bidens bipinnata 0–1 – spiderling BOERH2 Boerhavia 0–1 – yellow tackstem CAPA7 Calycoseris parryi 0–1 – white tackstem CAWR Calycoseris wrightii 0–1 – brittle spineflower CHBR Chorizanthe brevicornu 0–1 – devil's spineflower CHRI Chorizanthe rigida 0–1 – Esteve's pincushion CHST Chaenactis stevioides 0–1 – cryptantha CRYPT Cryptantha 0–1 – hairy prairie clover DAMO Dalea mollis 0–1 – western tansymustard DEPI Descurainia pinnata 0–1 – California shieldpod DICA7 Dithyrea californica 0–1 – flatcrown buckwheat ERDE6 Eriogonum deflexum 0–1 – miniature woollystar ERDI2 Eriastrum diffusum 0–1 – desert trumpet ERIN4 Eriogonum inflatum 0–1 – common woolly sunflower ERLA6 Eriophyllum lanatum 0–1 – kidneyleaf buckwheat ERRE3 Eriogonum reniforme 0–1 – desert sand verbena ABVI Abronia villosa 0–1 – onyxflower ACCO3 Achyronychia cooperi 0–1 – common fiddleneck AMMEI2 Amsinckia menziesii var. intermedia 0–1 – Shrub/Vine5 Dominant Shrubs 200–275 burrobush AMDU2 Ambrosia dumosa 150–200 – creosote bush LATRT Larrea tridentata var. tridentata 50–75 – 6 Misc. Shrubs 15–25 creosote bush LATR2 Larrea tridentata 50–75 – white ratany KRGR Krameria grayi 2–10 – whitestem paperflower PSCO2 Psilostrophe cooperi 1–3 – triangle bur ragweed AMDE4 Ambrosia deltoidea 1–3 – cattle saltbush ATPO Atriplex polycarpa 1–3 – button brittlebush ENFR Encelia frutescens 1–3 – littleleaf ratany KRER Krameria erecta 1–3 – 7 Other Shrubs 5–10 California croton CRCA5 Croton californicus 0–2 – longleaf jointfir EPTR Ephedra trifurca 0–1 – ocotillo FOSP2 Fouquieria splendens 0–1 – crown of thorns KOSP Koeberlinia spinosa 0–1 – water jacket LYAN Lycium andersonii 0–1 – desert ironwood OLTE Olneya tesota 0–1 – crucifixion thorn CAEM4 Castela emoryi 0–1 – 8 Succulents 15–25 branched pencil cholla CYRA9 Cylindropuntia ramosissima 2–5 – Wiggins' cholla CYEC3 Cylindropuntia echinocarpa 2–4 – devil cholla GREM Grusonia emoryi 1–4 – beavertail pricklypear OPBA2 Opuntia basilaris 1–3 – Christmas cactus CYLE8 Cylindropuntia leptocaulis 1–3 – saguaro CAGI10 Carnegiea gigantea 1–3 – buckhorn cholla CYACA2 Cylindropuntia acanthocarpa var. acanthocarpa 1–3 – Arizona pencil cholla CYAR14 Cylindropuntia arbuscula 1–2 – nightblooming cereus PEGRG Peniocereus greggii var. greggii 1–2 – Graham's nipple cactus MAGR9 Mammillaria grahamii 1–2 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 1–2 – Johnson's fishhook cactus ECJO3 Echinomastus johnsonii 1–2 – candy barrelcactus FEWI Ferocactus wislizeni 1–2 – Tree9 Trees 5–15 blue paloverde PAFL6 Parkinsonia florida 5–10 – yellow paloverde PAMI5 Parkinsonia microphylla 5–10 – Interpretations
Animal community
This site is usable for all classes of livestock. In areas where the site is not associated with sandy bottoms, summertime use by any livestock is not practical, due to lack of shady travel routes. The site produces year-round browse and grass for livestock. Water developments and fencing may be needed to permit grazing control.
Natural waters do not exist on the site. Water developments are very important to all wildlife species on the site. The sandy surfaces make this site home to a variety of burrowing birds, mammals and reptiles.Recreational uses
This site is located on large, nearly-level fan terraces. It has an abundance of wildflowers following both good winter and summer rainy seasons. The mixture of grasses, trees and shrubs enhances the aesthetics of these areas. Very few days in the fall, winter, or spring are too uncomfortable to enjoy outdoor activities. Jun-Aug afternoons, however, restrict activity. Horsebakc riding, wildlife observation, hunting, hiking, photography, camping and picnicking are activities suited to this site.
Supporting information
Type locality
Location 1: Maricopa County, AZ Township/Range/Section T7N R19W S36 General legal description La Posa Plain, Nine Mile Ranch Location 2: Maricopa County, AZ Township/Range/Section T8N R17W S34 General legal description La Posa Plain, Nine Mile Ranch Contributors
Larry D. Ellicott
Steve Barker
UnknownRangeland 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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