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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 florida
(2) Parkinsonia microphyllaShrub (1) Viguiera dentata
(2) Ambrosia dumosaHerbaceous (1) Pleuraphis rigida
(2) Muhlenbergia porteriPhysiographic features
This range site occurs in a bottom position. It benefits significantly from run-in moisture from adjacent areas and it suffers from moderate to rapid loss of run-off. It occurs on floodplains, alluvial fans and low terraces.
Table 2. Representative physiographic features
Landforms (1) Flood plain
(2) Alluvial fan
(3) Terrace
Elevation 23 – 305 m Slope 0 – 1 % 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) 180 mm BarLineFigure 1. Monthly precipitation range
BarLineFigure 2. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
Soils that are grouped together in this range site are deep to bedrock or other plant root restricting layers. Surface soil texture has a minimum depth of 10-15 inches and range in texture from loam to silty clay loam. Underlying layers have moderate to moderately slow permeability rates, but can absorb and hold all the moisture the climate supplies. Soluble salt accumulations are low. pH ranges from 7.9-8.4. With good vegetative cover, infiltration rates are high. Stability against erosion processes is moderate and plant-soil moisture relationships are good. Gravel may occur throughout the soil, but is less than 35% of the total soil volume.
Soils mapped on this site include: in SSA-649 Yuma-Wellton area MU's Gilman-9, Glenbar-10, Indio-16, Lagunita-19 & Ripley-16; SSA-653 Gila Bend-Ajo area MU Mohall Loam occasionally flooded-46.Table 4. Representative soil features
Parent material (1) Alluvium – granite
Surface texture (1) Loam
(2) Silty clay loam
Drainage class Well drained Permeability class Moderately slow to moderately rapid Soil depth 152 cm Surface fragment cover <=3" 0 – 35 % Surface fragment cover >3" Not specified Available water capacity
(0-101.6cm)21.34 – 28.96 cm Calcium carbonate equivalent
(0-101.6cm)1 – 10 % Electrical conductivity
(0-101.6cm)0 – 2 mmhos/cm Sodium adsorption ratio
(0-101.6cm)Not specified Soil reaction (1:1 water)
(0-101.6cm)7.9 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)Not specified 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 is a mixture of annual and perennial grasses and forbs, and scattered shrubs.
This site is favored by livestock due to accessibility, longer green period and nearness to water. When the plant cover is depleted, the site is very susceptible to sheet and gully erosion and woody plant invasion or increase, notably by mesquite and creosotebush. When gullied, much of the area once flooded no longer receives the extra moisture.Figure 3. Annual production by plant type (representative values) or group (midpoint values)
Table 5. Annual production by plant type
Plant type Low
(kg/hectare)Representative value
(kg/hectare)High
(kg/hectare)Grass/Grasslike 241 353 465 Shrub/Vine 56 95 135 Forb 39 59 78 Tree 4 13 22 Total 340 520 700 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 Perennial Grasses 196–353 bush muhly MUPO2 Muhlenbergia porteri 112–202 – big galleta PLRI3 Pleuraphis rigida 112–202 – 2 Threeawns 22–67 Santa Rita threeawn ARCAG Aristida californica var. glabrata 11–34 – poverty threeawn ARDI5 Aristida divaricata 11–34 – blue threeawn ARPUN Aristida purpurea var. nealleyi 11–34 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 11–34 – Wright's threeawn ARPUW Aristida purpurea var. wrightii 11–34 – spidergrass ARTE3 Aristida ternipes 11–34 – spidergrass ARTEG Aristida ternipes var. gentilis 11–34 – 3 Misc. Grasses 22–45 sixweeks threeawn ARAD Aristida adscensionis 0–11 – needle grama BOAR Bouteloua aristidoides 0–11 – sixweeks grama BOBA2 Bouteloua barbata 0–11 – Arizona brome BRAR4 Bromus arizonicus 0–11 – Arizona cottontop DICA8 Digitaria californica 6–11 – little barley HOPU Hordeum pusillum 0–11 – Mexican sprangletop LEFUU Leptochloa fusca ssp. uninervia 6–11 – Devils Canyon muhly MUAP Muhlenbergia appressa 0–11 – littleseed muhly MUMI Muhlenbergia microsperma 0–11 – Bigelow's bluegrass POBI Poa bigelovii 0–11 – plains bristlegrass SEVU2 Setaria vulpiseta 6–11 – spike dropseed SPCO4 Sporobolus contractus 6–11 – sand dropseed SPCR Sporobolus cryptandrus 6–11 – mesa dropseed SPFL2 Sporobolus flexuosus 6–11 – sixweeks fescue VUOC Vulpia octoflora 0–11 – Forb4 Misc. Forbs 22–45 blazingstar MENTZ Mentzelia 3–6 – wishbone-bush MILAV Mirabilis laevis var. villosa 3–6 – evening primrose OENOT Oenothera 3–6 – desert globemallow SPAM2 Sphaeralcea ambigua 3–6 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 3–6 – spear globemallow SPHA Sphaeralcea hastulata 3–6 – globemallow SPHAE Sphaeralcea 3–6 – brownplume wirelettuce STPA4 Stephanomeria pauciflora 3–6 – Louisiana vetch VILUL2 Vicia ludoviciana ssp. ludoviciana 3–6 – 5 Other Forbs 8–39 dwarf desertpeony ACNA2 Acourtia nana 0–1 – trailing windmills ALIN Allionia incarnata 0–1 – weakleaf bur ragweed AMCO3 Ambrosia confertiflora 0–1 – Menzies' fiddleneck AMME Amsinckia menziesii 0–1 – carelessweed AMPA Amaranthus palmeri 0–1 – milkvetch ASTRA Astragalus 0–1 – spiderling BOERH2 Boerhavia 0–1 – hoary bowlesia BOIN3 Bowlesia incana 0–1 – sand pygmyweed CRCOC Crassula connata var. connata 0–1 – cryptantha CRYPT Cryptantha 0–1 – fingerleaf gourd CUDI Cucurbita digitata 0–1 – desert thorn-apple DADI2 Datura discolor 0–1 – American wild carrot DAPU3 Daucus pusillus 0–1 – sacred thorn-apple DAWR2 Datura wrightii 0–1 – western tansymustard DEPI Descurainia pinnata 0–1 – bluedicks DICA14 Dichelostemma capitatum 0–1 – touristplant DIWI2 Dimorphocarpa wislizeni 0–1 – fetid marigold DYPA Dyssodia papposa 0–1 – miniature woollystar ERDI2 Eriastrum diffusum 0–1 – buckwheat ERIOG Eriogonum 0–1 – spurge EUPHO Euphorbia 0–1 – gilia GILIA Gilia 0–1 – Indian rushpea HOGL2 Hoffmannseggia glauca 0–1 – Gordon's bladderpod LEGO Lesquerella gordonii 0–1 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 0–1 – pepperweed LEPID Lepidium 0–1 – desert deervetch LOMI Lotus micranthus 0–1 – coastal bird's-foot trefoil LOSA Lotus salsuginosus 0–1 – Coulter's lupine LUSP2 Lupinus sparsiflorus 0–1 – Nuttall's povertyweed MONU Monolepis nuttalliana 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 – sleepy silene SIAN2 Silene antirrhina 0–1 – London rocket SIIR Sisymbrium irio 0–1 – woollyhead neststraw STMI2 Stylocline micropoides 0–1 – woolly tidestromia TILA2 Tidestromia lanuginosa 0–1 – Shrub/Vine6 Misc. Shrubs 39–78 San Felipe dogweed ADPO Adenophyllum porophylloides 6–12 – ambrosia leaf bur ragweed AMAM2 Ambrosia ambrosioides 6–12 – burrobush AMDU2 Ambrosia dumosa 6–12 – narrowleaf silverbush ARLA12 Argythamnia lanceolata 6–12 – fourwing saltbush ATCA2 Atriplex canescens 6–12 – cattle saltbush ATPO Atriplex polycarpa 6–12 – desertbroom BASA2 Baccharis sarothroides 6–12 – Coulter's brickellbush BRCO Brickellia coulteri 6–12 – Nevada jointfir EPNE Ephedra nevadensis 6–12 – longleaf jointfir EPTR Ephedra trifurca 6–12 – slender janusia JAGR Janusia gracilis 6–12 – white ratany KRGR Krameria grayi 6–12 – Mexican bladdersage SAME Salazaria mexicana 6–12 – toothleaf goldeneye VIDE3 Viguiera dentata 6–12 – 7 Succulents 4–13 saguaro CAGI10 Carnegiea gigantea 1–3 – buckhorn cholla CYACA2 Cylindropuntia acanthocarpa var. acanthocarpa 1–3 – Arizona pencil cholla CYAR14 Cylindropuntia arbuscula 1–3 – teddybear cholla CYBI9 Cylindropuntia bigelovii 1–3 – Wiggins' cholla CYEC3 Cylindropuntia echinocarpa 1–3 – Christmas cactus CYLE8 Cylindropuntia leptocaulis 1–3 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 1–3 – candy barrelcactus FEWI Ferocactus wislizeni 1–3 – 8 Other Shrubs 8–39 whitethorn acacia ACCO2 Acacia constricta 1–6 – catclaw acacia ACGR Acacia greggii 1–6 – crucifixion thorn CAEM4 Castela emoryi 1–6 – snakewood CONDA Condalia 1–6 – brittlebush ENFA Encelia farinosa 1–6 – Berlandier's wolfberry LYBE Lycium berlandieri 1–6 – desert-thorn LYCIU Lycium 1–6 – pale desert-thorn LYPA Lycium pallidum 1–6 – desert ironwood OLTE Olneya tesota 1–6 – honey mesquite PRGL2 Prosopis glandulosa 1–6 – Tree9 Tree 4–22 blue paloverde PAFL6 Parkinsonia florida 2–11 – yellow paloverde PAMI5 Parkinsonia microphylla 2–11 – Interpretations
Animal community
This site produces forage for year-round use and is easily traversed by all classes of cattle. Because of these factors and water availability, these areas are often overused. Mesquite readily increases on this site when the plant cover has bene depleted. Invader species include creosotebush. These areas are often productive enough to warrant fencing and water development and use as special use pastures. When scattered areas of this site occur with larger areas of unproductive areas (i.e., limy uplands, saline terraces), the entire area should be managed for the loamy bottom inclusions.
This site, being predominantly a grassland area, meets habitat requirements for small mammals and ground birds. Use by larger desert mammals is restricted to feeding and watering.Recreational uses
Land form consists of large swales, flats in canyon bottoms, components of large desert plains and loamy floodplains of the drainageways. This site is an open grassland with scattered trees and shrubs. In good winter precipitation years, spring wildflowers lend color. Very few days in the fall, winter or spring are too uncomfortable to enjoy outdoor activities. Afternoons Jun-Aug, however, are restricted due to heat. Horseback riding, wildlife observation, hunting, hiking, picnicking and photography are the main uses suited to the site.
Other information
Extensively used for cropland where irrigation water is available.
Supporting information
Type locality
Location 1: Mohave County, AZ Township/Range/Section T11N R12W S9 General legal description Eagle Tail Ranch Contributors
Larry D. Ellicott
Stephen Cassady
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:
Uncommon. -
Presence of water flow patterns:
Water flow patterns are uncommon, highly variable and a function of upland runoff. -
Number and height of erosional pedestals or terracettes:
None. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
5-50%. Lower values expected in El Nino years. -
Number of gullies and erosion associated with gullies:
Uncommon. -
Extent of wind scoured, blowouts and/or depositional areas:
No evidence of soil movement by wind. -
Amount of litter movement (describe size and distance expected to travel):
Herbaceous litter can move by water when high flows are received. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil surface resisitance to erosion is good. Expect values of 1-3 in plant interspaces, 4-6 in plant canopies. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Weak thin platy to granular to subangular blocky with depth; 7.5-10YR6/4 dry, 7.5-10YR4/4 moist; thickness to 6 inches. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
15-25% canopy; 70-75% shrubs, 25-30% trees. -
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:
shrubs > trees > winter annuals > summer annuals > perennial forbs.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. -
Average percent litter cover (%) and depth ( in):
Hervaceous litter is not persistent on the site and may be 35-60% in El Nino years. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
304 lbs/ac unfavorable precipitation; 465 lbs/ac normal precipitation; 625 lbs/ac favorable precipitation. -
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), London Rocket, Cheeseweed. -
Perennial plant reproductive capability:
Not impaired for trees and shrubs.
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