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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): 040X–Sonoran Basin and Range
AZ 40.2 – Middle Sonoran Desert
Elevations range from 1200 to 2000 feet and precipitation averages 7 to 10 inches per year. Vegetation includes saguaro, palo verde, creosotebush, triangle bursage, brittlebush, prickly pear, cholla, desert saltbush, wolfberry bush muhly, threeawns, 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 Not specified
Shrub Not specified
Herbaceous Not specified
Physiographic features
This site occurs on fan terraces and stream terraces. Slopes are from 1% to 8%. Elevations range from 1000 to 2200.
Table 2. Representative physiographic features
Landforms (1) Fan
(2) Terrace
(3) Stream terrace
Elevation 1000 – 2200 ft Slope 1 – 8 % Climatic features
Precipitation in the sub-resource area ranges from 7 to 10 inches. Elevations range from 900 to 2050 feet. Winter-summer rainfall ratios range from 40% to 60% in the southern part along the international boundary, to 60% to 40% in the central and northern parts of the sub-resource area. 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 38% at Florence and 46% at Aguila. Summer rains fall July- September, originate in the Gulf of Mexico, and are convective, usually brief, intense thunderstorms. Summer precipitation is extremely erratic and undependable in this area. Cool season moisture tends to be frontal, originates in the Pacific and Gulf of California, and falls in widespread storms with long duration and low intensity. This is the dependable moisture supply for vegetation in the area. Snow is very rare and usually melts on contact. May-June is the driest time of the year. Humidity is very low.
Winter temperatures are very mild with very few days recording freezing for short periods of time. Summertime temperatures are hot to very hot with many days in June-July exceeding 105 degrees F. Frost-free days range from 280 at stations in major river valleys with cold air drainage to 320 to 350 days at upland stations.
Both the spring and the summer growing seasons are equally important for perennial grass, forb and shrub growth. Cool and warm season annual forbs and grasses can be common in their respective seasons with above average rainfall. Perennial forage species can remain green throughout the year with available moisture.Table 3 Representative climatic features
Frost-free period (average) 350 days Freeze-free period (average) 0 days Precipitation total (average) 10 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
These are deep soils formed in loamy alluvium of mixed origin. Surface textures range from sandy loam to very gravelly sandy loam and must be as thick or thicker than four inches (eight inches for GRV-SL). They have clay argillic or cambic horizons at shallow depths. They are non-calcareous in the surface, slightly below. Plant-soil moisture relationships are good. Soils mapped on this site include Mohall sandy loam and Tremant sandy loam.
Table 4. Representative soil features
Surface texture (1) Gravelly sandy loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately slow Soil depth 60 in Surface fragment cover <=3" 5 – 15 % Surface fragment cover >3" Not specified Available water capacity
(0-40in)7.2 – 9 in Calcium carbonate equivalent
(0-40in)2 – 25 % Electrical conductivity
(0-40in)Not specified Sodium adsorption ratio
(0-40in)Not specified Soil reaction (1:1 water)
(0-40in)7.4 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)5 – 15 % 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 the 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
Historical Climax Plant CommunityCommunity 1.1
Historical Climax Plant CommunityThe potential plant community on this site is a mixture of desert trees, shrubs and cacti with perennial and annual forbs and grasses. The aspect is shrubland.
Perennial, herbaceous, forage species like; bush muhly, big galleta, threeawn and globemallow are quickly removed from the plant community with heavy grazing. Continued heavy grazing use can result in a decrease in white bursage followed by an increase in triangle bursage or cacti species. A few introduced, cool season, annual grasses and forbs like; filaree, Mediterranean grass and London rocket mustard have become entrenched on areas of this site and compete with native annual grasses and forbs. Tree species on this site are shrubby in nature due to clayey horizons near the soil surface. The coarse textured (SL, GRSL) surfaces act to trap intense summer precipitation and let it slowly infiltrate the clayey textured subsurface horizons making the site a fairly good user of summer rainfall and suitable habitat for shallow rooted, warm season perennials. The surfaces of these soils usually lack an effective cover of gravels. Plant populations for major shrub species are; from 2 to 10 plants per acre for the tree group, 750 to 1000 plants per acre for white bursage, and 100 to 600 plants per acre for creosotebush.
Figure 4. 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 275 – 375 Grass/Grasslike 50 – 125 Forb 50 – 75 Total 375 – 575 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 50–75 bush muhly MUPO2 Muhlenbergia porteri 30–50 – big galleta PLRI3 Pleuraphis rigida 10–20 – 2 5–25 purple threeawn ARPU9 Aristida purpurea 0–5 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 0–5 – Wright's threeawn ARPUW Aristida purpurea var. wrightii 0–3 – spidergrass ARTE3 Aristida ternipes 0–1 – spidergrass ARTEG Aristida ternipes var. gentilis 0–1 – low woollygrass DAPU7 Dasyochloa pulchella 0–1 – Arizona cottontop DICA8 Digitaria californica 0–1 – plains bristlegrass SEVU2 Setaria vulpiseta 0–1 – sand dropseed SPCR Sporobolus cryptandrus 0–1 – mesa dropseed SPFL2 Sporobolus flexuosus 0–1 – slim tridens TRMU Tridens muticus 0–1 – blue threeawn ARPUN Aristida purpurea var. nealleyi 0–1 – Santa Rita threeawn ARCAG Aristida californica var. glabrata 0–1 – 3 5–50 sixweeks threeawn ARAD Aristida adscensionis 0–10 – needle grama BOAR Bouteloua aristidoides 0–10 – sixweeks grama BOBA2 Bouteloua barbata 0–10 – Rothrock's grama BORO2 Bouteloua rothrockii 0–10 – prairie threeawn AROL Aristida oligantha 0–5 – Eastwood fescue VUMIC Vulpia microstachys var. ciliata 0–5 – Pacific fescue VUMIP Vulpia microstachys var. pauciflora 0–5 – sixweeks fescue VUOC Vulpia octoflora 0–5 – Arizona brome BRAR4 Bromus arizonicus 0–1 – feather fingergrass CHVI4 Chloris virgata 0–1 – canyon cupgrass ERLE7 Eriochloa lemmonii 0–1 – desert lovegrass ERPEM Eragrostis pectinacea var. miserrima 0–1 – tufted lovegrass ERPEP2 Eragrostis pectinacea var. pectinacea 0–1 – Mexican sprangletop LEFUU Leptochloa fusca ssp. uninervia 0–1 – mucronate sprangletop LEPA6 Leptochloa panicea 0–1 – delicate muhly MUFR Muhlenbergia fragilis 0–1 – littleseed muhly MUMI Muhlenbergia microsperma 0–1 – Bigelow's bluegrass POBI Poa bigelovii 0–1 – Arizona signalgrass URAR Urochloa arizonica 0–1 – Forb4 50–75 Emory's globemallow SPEM Sphaeralcea emoryi 0–5 – desert globemallow SPAM2 Sphaeralcea ambigua 0–5 – buckwheat ERIOG Eriogonum 0–5 – bristly fiddleneck AMTE3 Amsinckia tessellata 0–3 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 0–3 – desert trumpet ERIN4 Eriogonum inflatum 0–3 – globemallow SPHAE Sphaeralcea 0–2 – woollyhead neststraw STMI2 Stylocline micropoides 0–1 – brownplume wirelettuce STPA4 Stephanomeria pauciflora 0–1 – sand fringepod THCU Thysanocarpus curvipes 0–1 – cutleaf thelypody THLA Thelypodium laciniatum 0–1 – woolly tidestromia TILA2 Tidestromia lanuginosa 0–1 – brownfoot ACWR5 Acourtia wrightii 0–1 – weakleaf bur ragweed AMCO3 Ambrosia confertiflora 0–1 – fringed amaranth AMFI Amaranthus fimbriatus 0–1 – common fiddleneck AMMEI2 Amsinckia menziesii var. intermedia 0–1 – carelessweed AMPA Amaranthus palmeri 0–1 – milkweed ASCLE Asclepias 0–1 – milkvetch ASTRA Astragalus 0–1 – wheelscale saltbush ATEL Atriplex elegans 0–1 – wheelscale saltbush ATELF Atriplex elegans var. fasciculata 0–1 – Wright's saltbush ATWR Atriplex wrightii 0–1 – desert marigold BAMU Baileya multiradiata 0–1 – Coulter's spiderling BOCO2 Boerhavia coulteri 0–1 – spiderling BOERH2 Boerhavia 0–1 – hoary bowlesia BOIN3 Bowlesia incana 0–1 – exserted Indian paintbrush CAEXE Castilleja exserta ssp. exserta 0–1 – yellow tackstem CAPA7 Calycoseris parryi 0–1 – white tackstem CAWR Calycoseris wrightii 0–1 – whitemargin sandmat CHAL11 Chamaesyce albomarginata 0–1 – lambsquarters CHAL7 Chenopodium album 0–1 – brittle spineflower CHBR Chorizanthe brevicornu 0–1 – aridland goosefoot CHDE Chenopodium desiccatum 0–1 – hyssopleaf sandmat CHHY3 Chamaesyce hyssopifolia 0–1 – devil's spineflower CHRI Chorizanthe rigida 0–1 – sand pygmyweed CRCOC Crassula connata var. connata 0–1 – cryptantha CRYPT Cryptantha 0–1 – hairy prairie clover DAMO Dalea mollis 0–1 – American wild carrot DAPU3 Daucus pusillus 0–1 – western tansymustard DEPI Descurainia pinnata 0–1 – touristplant DIWI2 Dimorphocarpa wislizeni 0–1 – flatcrown buckwheat ERDE6 Eriogonum deflexum 0–1 – miniature woollystar ERDI2 Eriastrum diffusum 0–1 – erigenia ERIGE Erigenia 0–1 – woolly sunflower ERIOP2 Eriophyllum 0–1 – Texas stork's bill ERTE13 Erodium texanum 0–1 – California poppy ESCAM Eschscholzia californica ssp. mexicana 0–1 – pygmy poppy ESMI Eschscholzia minutiflora 0–1 – spurge EUPHO Euphorbia 0–1 – hairy desertsunflower GECA2 Geraea canescens 0–1 – gilia GILIA Gilia 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 – pepperweed LEPID Lepidium 0–1 – foothill deervetch LOHU2 Lotus humistratus 0–1 – desert deervetch LOMI Lotus micranthus 0–1 – Arizona lupine LUAR4 Lupinus arizonicus 0–1 – Coulter's lupine LUSP2 Lupinus sparsiflorus 0–1 – disc mayweed MADI6 Matricaria discoidea 0–1 – lacy tansyaster MAPIP4 Machaeranthera pinnatifida ssp. pinnatifida var. pinnatifida 0–1 – bristly nama NAHI Nama hispidum 0–1 – glandular threadplant NEGL Nemacladus glanduliferus 0–1 – evening primrose OENOT Oenothera 0–1 – Florida pellitory PAFL3 Parietaria floridana 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 – doubleclaw PRPA2 Proboscidea parviflora 0–1 – New Mexico plumeseed RANE Rafinesquia neomexicana 0–1 – sleepy silene SIAN2 Silene antirrhina 0–1 – 5 5–25 Alga 2ALGA Alga 5–15 – Lichen 2LICHN Lichen 1–5 – Moss 2MOSS Moss 1–3 – Fungus 2FUNGI Fungus 1–2 – Shrub/Vine6 100–150 burrobush AMDU2 Ambrosia dumosa 100–150 – 8 100–150 creosote bush LATR2 Larrea tridentata 75–100 – cattle saltbush ATPO Atriplex polycarpa 25–50 – 9 25–50 triangle bur ragweed AMDE4 Ambrosia deltoidea 5–15 – white ratany KRGR Krameria grayi 5–10 – littleleaf ratany KRER Krameria erecta 2–5 – Nevada jointfir EPNE Ephedra nevadensis 0–2 – water jacket LYAN Lycium andersonii 0–2 – Berlandier's wolfberry LYBE Lycium berlandieri 0–2 – Arizona desert-thorn LYEX Lycium exsertum 0–2 – whitestem paperflower PSCO2 Psilostrophe cooperi 0–1 – Mexican bladdersage SAME Salazaria mexicana 0–1 – arrow poision plant SEBI9 Sebastiania bilocularis 0–1 – lotebush ZIOB Ziziphus obtusifolia 0–1 – ocotillo FOSP2 Fouquieria splendens 0–1 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–1 – alkali goldenbush ISACA2 Isocoma acradenia var. acradenia 0–1 – southern goldenbush ISPL Isocoma pluriflora 0–1 – burroweed ISTE2 Isocoma tenuisecta 0–1 – fourwing saltbush ATCA2 Atriplex canescens 0–1 – desertbroom BASA2 Baccharis sarothroides 0–1 – crucifixion thorn CAEM4 Castela emoryi 0–1 – whitethorn acacia ACCO2 Acacia constricta 0–1 – rayless goldenhead ACSP Acamptopappus sphaerocephalus 0–1 – Tucson bur ragweed AMCO4 Ambrosia cordifolia 0–1 – 10 5–25 Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 0–2 – candy barrelcactus FEWI Ferocactus wislizeni 0–2 – senita cactus PASC14 Pachycereus schottii 0–1 – nightblooming cereus PEGR3 Peniocereus greggii 0–1 – organpipe cactus STTH3 Stenocereus thurberi 0–1 – beavertail pricklypear OPBA2 Opuntia basilaris 0–1 – Tree7 25–50 yellow paloverde PAMI5 Parkinsonia microphylla 5–20 – velvet mesquite PRVE Prosopis velutina 5–15 – desert ironwood OLTE Olneya tesota 5–15 – Interpretations
Animal community
This site produces forage for year round use when in excellent or good range condition. Perennial grasses like bush muhly and big galleta provide energy and useable browse species like white bursage provide protein and complement each other in the diets of range livestock. In wet winters the production of cool season annual forbs and grasses can be high and provides for considerable extra grazing capacity in the March-May season.
Water developments are very important to wildlife species on this site. Cover and diversity are lacking for the larger desert mammals. The site is home to a large variety of small mammals, reptiles and their predators.Other information
T&E: Antilocapra Americana sonoriensis
(Sonoran pronghorn)
Leptonycteris curasoae yerbebuena
(Lessser long-nosed bat)Supporting information
Type locality
Location 1: Maricopa County, AZ Township/Range/Section T7N R15W S12 General legal description Phoenix FO - Butler Valley SE 1/4 Sec. 12 Location 2: Pima County, AZ Township/Range/Section T15S R2W S29 General legal description Sells FO - Pisinimo Dist. Location 3: Maricopa County, AZ Township/Range/Section T4N R3W S35 General legal description Phoenix FO - north of White Tank Mtns. Location 4: Pima County, AZ Township/Range/Section T14S R6W S20 General legal description Tucson FO - Organ Pipe National Monument Location 5: Pinal County, AZ Township/Range/Section T5S R8E S16 General legal description Casa Grande FO - Casa Grande National Monument Contributors
Dan Robinett
Dan Robinett, J. Norris
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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