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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 40.3 – 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 Not specified
Shrub (1) Krameria grayi
(2) Ambrosia dumosaHerbaceous (1) Pleuraphis rigida
(2) Muhlenbergia porteriPhysiographic features
This range site always occurs in an upland position on floodplains, low terraces and broad old alluvial plains. The Wellton and dateland soils do not benefit from moisture from adjacent areas, whereas the Antho soil does. Soils do not suffer from excessive loss from runoff.
Table 2. Representative physiographic features
Landforms (1) Flood plain
(2) Terrace
(3) Alluvial flat
Elevation 75 – 1200 ft Slope 0 – 3 % Aspect Aspect is not a significant factor 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 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
Soils are deep to bedrock or other plant root restricting layers. Surface soils range in depth of 4-8 inches, with textures of sandy loam, fine sandy loam and loamy sand. The subsoil and underlying layers have a moderate to moderately rapid permeability, but can absorb and hold the moisture the climate supplies. Soluble salt accumulations ae low. the pH ranges from 7.9-8.4. With good vegetation cover, infiltration rates are high. Stability against erosion processes is good. Plant-Soil moisture relationships ae good. Percent coarse fragment ranges from 15-35% in Denure and Pahaka, and less than 15% in the Dateland soils.
Soils mapped on this site include: in SSA-627 Southern Mohave county MU's Coolidge-38 & Denure-38; SSA-645 Aguila-Carefree area MU's Antho-4, Carrizo-15 & 30, Denure-30, Maripo-4, Momoli-30; SSA-653 Gila Bend-Ajo area MU's Dateland-13 & Denure SL-16.Table 4. Representative soil features
Surface texture (1) Sandy loam
(2) Fine sandy loam
(3) Loamy sand
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately slow to moderately rapid Soil depth 60 in Surface fragment cover <=3" 5 – 15 % Surface fragment cover >3" Not specified Available water capacity
(0-40in)7.2 – 10.2 in Calcium carbonate equivalent
(0-40in)1 – 25 % Electrical conductivity
(0-40in)Not specified 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)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 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 plant community on this site is a mixture of desert shrubs and trees with an understory of perennial grasses. Winter and summer annual grasses and forbs are abundant in years with above average moisture in their respective seasons.
Continued grazing use furing the various growing seaasons results in a decline in perennial grasses and an increase of woody species such as triangle bursage and creosotebush. The absence of natural fires may also be responsible for woody plant increases.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 130 185 240 Grass/Grasslike 100 160 220 Forb 40 50 60 Total 270 395 520 Figure 5. 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/Grasslike0 Dominant Perennial Grasses 70–150 big galleta PLRI3 Pleuraphis rigida 60–120 – bush muhly MUPO2 Muhlenbergia porteri 10–30 – 1 Misc. Perennial Grasses 10–30 sand dropseed SPCR Sporobolus cryptandrus 2–7 – mesa dropseed SPFL2 Sporobolus flexuosus 2–7 – California threeawn ARCA9 Aristida californica 2–3 – Santa Rita threeawn ARCAG Aristida californica var. glabrata 2–3 – poverty threeawn ARDI5 Aristida divaricata 2–3 – blue threeawn ARPUN Aristida purpurea var. nealleyi 2–3 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 2–3 – Wright's threeawn ARPUW Aristida purpurea var. wrightii 2–3 – spidergrass ARTE3 Aristida ternipes 2–3 – spidergrass ARTEG Aristida ternipes var. gentilis 2–3 – 2 Annual Grasses 20–40 needle grama BOAR Bouteloua aristidoides 3–6 – sixweeks grama BOBA2 Bouteloua barbata 3–6 – Arizona brome BRAR4 Bromus arizonicus 3–6 – low woollygrass DAPU7 Dasyochloa pulchella 2–5 – littleseed muhly MUMI Muhlenbergia microsperma 2–5 – Bigelow's bluegrass POBI Poa bigelovii 2–5 – sixweeks threeawn ARAD Aristida adscensionis 2–5 – Forb3 Forbs 40–60 glandular threadplant NEGL Nemacladus glanduliferus 5–8 – evening primrose OENOT Oenothera 5–8 – globemallow SPHAE Sphaeralcea 5–8 – milkweed ASCLE Asclepias 5–8 – milkvetch ASTRA Astragalus 5–8 – spiderling BOERH2 Boerhavia 5–8 – cryptantha CRYPT Cryptantha 5–8 – erigenia ERIGE Erigenia 5–8 – buckwheat ERIOG Eriogonum 5–8 – cottongrass ERIOP Eriophorum 5–8 – spurge EUPHO Euphorbia 5–8 – gilia GILIA Gilia 5–8 – pepperweed LEPID Lepidium 5–8 – Coulter's lupine LUSP2 Lupinus sparsiflorus 5–8 – pellitory PARIE Parietaria 1–5 – strigose bird's-foot trefoil LOSTT Lotus strigosus var. tomentellus 0–5 – orphniospora lichen ORPHN Orphniospora 0–3 – woollyhead neststraw STMI2 Stylocline micropoides 1–3 – cutleaf thelypody THLA Thelypodium laciniatum 1–3 – woolly tidestromia TILA2 Tidestromia lanuginosa 1–3 – combseed PECTO Pectocarya 0–3 – manybristle chinchweed PEPA2 Pectis papposa 1–3 – phacelia PHACE Phacelia 0–3 – desert Indianwheat PLOV Plantago ovata 1–3 – New Mexico plumeseed RANE Rafinesquia neomexicana 1–3 – sleepy silene SIAN2 Silene antirrhina 1–3 – London rocket SIIR Sisymbrium irio 0–3 – desert globemallow SPAM2 Sphaeralcea ambigua 1–3 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 1–3 – Emory's globemallow SPEM Sphaeralcea emoryi 0–3 – Lindley's silverpuffs MILI5 Microseris lindleyi 1–3 – foothill deervetch LOHU2 Lotus humistratus 1–3 – Gordon's bladderpod LEGO Lesquerella gordonii 1–3 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 1–3 – California poppy ESCAM Eschscholzia californica ssp. mexicana 1–3 – pygmy poppy ESMI Eschscholzia minutiflora 1–3 – desert trumpet ERIN4 Eriogonum inflatum 1–3 – brownfoot ACWR5 Acourtia wrightii 1–3 – common fiddleneck AMMEI2 Amsinckia menziesii var. intermedia 1–3 – bristly fiddleneck AMTE3 Amsinckia tessellata 1–3 – American wild carrot DAPU3 Daucus pusillus 1–3 – western tansymustard DEPI Descurainia pinnata 1–3 – miniature woollystar ERDI2 Eriastrum diffusum 1–3 – hoary bowlesia BOIN3 Bowlesia incana 1–3 – exserted Indian paintbrush CAEXE Castilleja exserta ssp. exserta 1–3 – brittle spineflower CHBR Chorizanthe brevicornu 1–3 – devil's spineflower CHRI Chorizanthe rigida 1–3 – Shrub/Vine4 Dominant Shrubs 100–180 burrobush AMDU2 Ambrosia dumosa 40–80 – white ratany KRGR Krameria grayi 60–80 – creosote bush LATRT Larrea tridentata var. tridentata 20–40 – 5 Misc. Shrubs 20–40 whitethorn acacia ACCO2 Acacia constricta 5–8 – catclaw acacia ACGR Acacia greggii 5–8 – cattle saltbush ATPO Atriplex polycarpa 5–8 – longleaf jointfir EPTR Ephedra trifurca 4–8 – lotebush ZIOBO Ziziphus obtusifolia var. obtusifolia 3–7 – 6 Succulents 4–20 crucifixion thorn CAEM4 Castela emoryi 1–2 – saguaro CAGI10 Carnegiea gigantea 1–2 – buckhorn cholla CYACA2 Cylindropuntia acanthocarpa var. acanthocarpa 1–2 – Wiggins' cholla CYEC3 Cylindropuntia echinocarpa 1–2 – Christmas cactus CYLE8 Cylindropuntia leptocaulis 1–2 – branched pencil cholla CYRA9 Cylindropuntia ramosissima 1–2 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 1–2 – Emory's barrel cactus FEEM Ferocactus emoryi 1–2 – candy barrelcactus FEWI Ferocactus wislizeni 1–2 – crown of thorns KOSP Koeberlinia spinosa 1–2 – globe cactus MAMMI Mammillaria 1–2 – beavertail pricklypear OPBA2 Opuntia basilaris 1–2 – Interpretations
Animal community
This site produces year-round forage in good or better condition and is suited to year-long use. It is easily traversed by cows, calves, or stocker cattle. This site will be one of the first upland sites to respond to grazing management. Fencing and water developments (well & pipeline) are important on these areas to permit grazing management.
This site doesn't provide all the elements for good wildlife habitat; however, the site is usually near bottom sites or cultivated areas that provide feed, cover and water.Recreational uses
This site is located on large, relatively flat, plains and alluvial fans. It has an abundance of wild flowers following both good winter and summer rainy seasons. The mixture of grasses, trees and shrubs enhances the aesthetics of the area. Very few days in the fall, winter or spring are too uncomfortable to enjoy outdoor activities; however, Jun-Aug after lunch heat restricts activity. The site is suited to horseback riding, wildlife observation, hunting, hiking, photography, camping and picnicking.
Supporting information
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) Dave Womack, Dan Robinett, Emilio Carrillo. Contact for lead author NRCS Tucson Area Office Date 03/07/2005 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
Rills are common, widely spaced, and coninuous in absence of high gravel cover. -
Presence of water flow patterns:
Water flow patterns are common, continuous and occupy 15-20% of area. -
Number and height of erosional pedestals or terracettes:
Shrubs have symmetrical mounds caused by actions of splash, erosion, and rodent activity. There are no pedestals on rock or gravel fragments and no terracettes. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground is 10-60%. Expect low values in dry years. -
Number of gullies and erosion associated with gullies:
None. -
Extent of wind scoured, blowouts and/or depositional areas:
No evidence. -
Amount of litter movement (describe size and distance expected to travel):
Herbaceous litter can move by wind and water. Woody litter remains under shrub canopies. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil surface resistance to erosion is good under shrub canopies to moderate in interspaces due to crusts formed by raindrop impact. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Weak thin platy to granular; 7.5-10YR5/3 dry; 7.5-10YR4/3 moist, to 6 inches. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Canopy 10-15%. Herbaceous litter is present in some years and absent in others. Large shrubs with large coppice mounds with high infiltration rates. Subshrubs with small mounds with high infiltration rates. Mounds occupy 10-15% of the surface and are evenly spaced over the area. -
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:
Large shrubs > subshrubs > perennial grasses > winter annuals > summer annuals > succulents (note: in El Nino years, annual forbs and grasses are #1 in above ground weight.)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):
30-70% canopy mortality on trees and shrubs; 90-100% mortality on perennial grasses. -
Average percent litter cover (%) and depth ( in):
Herbaceous litter is not persistent on the site, but may be in El Nino years. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
270 lbs/ac unfavorable precipitation; 395 lbs/ac normal precipitation; 520 lbs/ac favorable precipitatio. -
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:
Sahara mustard (potential), schismus -
Perennial plant reproductive capability:
Not impaired for shrubs; drought impaired for perennial grasses and forbs.
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