Natural Resources
Conservation Service
Ecological site R040XB225AZ
Loamy Upland, Saline 7"-10" p.z.
Accessed: 11/13/2024
General information
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.
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 |
(1) Atriplex polycarpa |
| Herbaceous |
(1) Sporobolus airoides |
Physiographic features
This site occurs as nearly level to gently sloping stream terraces and relict basin floors.
Table 2. Representative physiographic features
| Landforms |
(1)
Stream terrace
(2) Basin floor |
|---|---|
| Elevation | 1,000 – 2,050 ft |
| Slope | 5% |
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 |
Figure 2. Monthly precipitation range
Figure 3. Monthly average minimum and maximum temperature
Influencing water features
Soil features
Soils are deep, well drained saline and sodic soils. They are loamy to clayey with a surface of silt loam to loam. Surface texture may be clayloam. Subsurface texture may be fine silty, fine, fine or coarse loamy. Included are soils with a cap of fine sandy loam, but with textural change to heavier horizons at less than 20". Plant-soil moisture relationships are fair. Water infiltration rates are good, but saline-sodic conditions limit the amount of soil moisture available for plant growth. This site is mapped in 6 Soil Survey areas in Southwestern Arizona in the CRA D40-2.
Soils mapped on this site include: SSA-645 Aguila-Carefree area MU Sal-106; SSA-651 Central Maricopa county MU Casa Grande-Cg, Ch, Ck & Cm, Estrella-Et, Harqua-HAB, HAC, HLC, HM, HrB & RhB, La Palma-La & PvB, Laveen (saline)-Cm, Ld & Lf, and Perryville-Pb; SSA-658 Gila River Indian Reservation MU's Casa Grande-7, 8 & 30, Dateland (saline)-12, Indio (unflooded)-18, 19 & 37, Kamato (unflooded)-20 & 21, Laveen (saline)-23, Tatai (unflooded)-33; SSA-659 Western Pinal county MU's Casa Grande-3 & 4, Dateland (saline)-14, La Palma-27, Toltec (saline)-43; SSA-661 Eastern Pinal-Southern Gila counties MU Casa Grande-860; SSA-703 Tohono O'odham MU Casa Grande-8 & 9.
Table 4. Representative soil features
| Surface texture |
(1) Loam (2) Silt loam (3) Silty clay loam |
|---|---|
| Family particle size |
(1) Loamy |
| Drainage class | Well drained |
| Permeability class | Very slow to moderately rapid |
| Soil depth | 60 in |
| Surface fragment cover <=3" | 5% |
| Surface fragment cover >3" | Not specified |
| Available water capacity (0-40in) |
9.6 – 11.4 in |
| Calcium carbonate equivalent (0-40in) |
1 – 10% |
| Electrical conductivity (0-40in) |
2 – 16 mmhos/cm |
| Sodium adsorption ratio (0-40in) |
13 – 30 |
| Soil reaction (1:1 water) (0-40in) |
7.9 – 11 |
| Subsurface fragment volume <=3" (Depth not specified) |
5% |
| 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 grazing, fire, 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 shown for the group. Divide the resulting total by the total normal year production shown in the plant community description. If 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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Ecosystem states
State 1 submodel, plant communities
State 1
Historic Climax Plant Community
Community 1.1
Historic Climax Plant Community
The native plant community on this site is dominated by a mixture of low, salt tolerant shrubs. Winter annual forbs are fairly well represented on the site. Perennial grasses occur in trace amounts in the potential community. Cryptogam (lichen and moss) cover is high. With severe disturbance such as heavy continuous grazing, the saltbush species are replaced by less palatable perennials like dogturd cholla, seepweed and annuals. The Atriplex species are very sensitive to summer fires. Loss of shrub cover can lead to accellerated water erosion.
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 | 300 | 340 | 380 |
| Forb | 8 | 34 | 60 |
| Grass/Grasslike | 8 | 24 | 40 |
| Total | 316 | 398 | 480 |
Additional community tables
Table 6. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (lb/acre) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Grass/Grasslike
|
||||||
| 1 | 8–40 | |||||
| sixweeks threeawn | ARAD | Aristida adscensionis | 0–2 | – | ||
| Havard's threeawn | ARHA3 | Aristida havardii | 0–2 | – | ||
| prairie threeawn | AROL | Aristida oligantha | 0–2 | – | ||
| spidergrass | ARTE3 | Aristida ternipes | 0–2 | – | ||
| needle grama | BOAR | Bouteloua aristidoides | 0–2 | – | ||
| sixweeks grama | BOBA2 | Bouteloua barbata | 0–2 | – | ||
| Rothrock's grama | BORO2 | Bouteloua rothrockii | 0–2 | – | ||
| feather fingergrass | CHVI4 | Chloris virgata | 0–2 | – | ||
| tufted lovegrass | ERPEP2 | Eragrostis pectinacea var. pectinacea | 0–2 | – | ||
| little barley | HOPU | Hordeum pusillum | 0–2 | – | ||
| Mexican sprangletop | LEFUU | Leptochloa fusca ssp. uninervia | 0–2 | – | ||
| mucronate sprangeltop | LEPAB | Leptochloa panicea ssp. brachiata | 0–2 | – | ||
| littleseed muhly | MUMI | Muhlenbergia microsperma | 0–2 | – | ||
| bush muhly | MUPO2 | Muhlenbergia porteri | 0–2 | – | ||
| Bigelow's bluegrass | POBI | Poa bigelovii | 0–2 | – | ||
| alkali sacaton | SPAI | Sporobolus airoides | 0–2 | – | ||
| sixweeks fescue | VUOC | Vulpia octoflora | 0–2 | – | ||
|
Forb
|
||||||
| 2 | 8–20 | |||||
| desert Indianwheat | PLOV | Plantago ovata | 8–20 | – | ||
| 3 | 8–40 | |||||
| weakleaf bur ragweed | AMCO3 | Ambrosia confertiflora | 0–3 | – | ||
| fringed amaranth | AMFI | Amaranthus fimbriatus | 0–3 | – | ||
| common fiddleneck | AMMEI2 | Amsinckia menziesii var. intermedia | 0–3 | – | ||
| wheelscale saltbush | ATEL | Atriplex elegans | 0–3 | – | ||
| wheelscale saltbush | ATELF | Atriplex elegans var. fasciculata | 0–3 | – | ||
| Coulter's spiderling | BOCO2 | Boerhavia coulteri | 0–3 | – | ||
| hoary bowlesia | BOIN3 | Bowlesia incana | 0–3 | – | ||
| yellow tackstem | CAPA7 | Calycoseris parryi | 0–3 | – | ||
| white tackstem | CAWR | Calycoseris wrightii | 0–3 | – | ||
| aridland goosefoot | CHDE | Chenopodium desiccatum | 0–3 | – | ||
| cryptantha | CRYPT | Cryptantha | 0–3 | – | ||
| American wild carrot | DAPU3 | Daucus pusillus | 0–3 | – | ||
| miniature woollystar | ERDI2 | Eriastrum diffusum | 0–3 | – | ||
| Gordon's bladderpod | LEGO | Lesquerella gordonii | 0–3 | – | ||
| pepperweed | LEPID | Lepidium | 0–3 | – | ||
| coastal bird's-foot trefoil | LOSA | Lotus salsuginosus | 0–3 | – | ||
| Coulter's lupine | LUSP2 | Lupinus sparsiflorus | 0–3 | – | ||
| Nuttall's povertyweed | MONU | Monolepis nuttalliana | 0–3 | – | ||
| combseed | PECTO | Pectocarya | 0–3 | – | ||
| phacelia | PHACE | Phacelia | 0–3 | – | ||
| New Mexico plumeseed | RANE | Rafinesquia neomexicana | 0–3 | – | ||
| canaigre dock | RUHY | Rumex hymenosepalus | 0–3 | – | ||
| sleepy silene | SIAN2 | Silene antirrhina | 0–3 | – | ||
| Coulter's globemallow | SPCO2 | Sphaeralcea coulteri | 0–3 | – | ||
| woollyhead neststraw | STMI2 | Stylocline micropoides | 0–3 | – | ||
| woolly tidestromia | TILA2 | Tidestromia lanuginosa | 0–3 | – | ||
|
Shrub/Vine
|
||||||
| 4 | 204–272 | |||||
| thinleaf fourwing saltbush | ATCAL4 | Atriplex canescens var. linearis | 204–272 | – | ||
| cattle saltbush | ATPO | Atriplex polycarpa | 204–272 | – | ||
| 5 | 34–68 | |||||
| iodinebush | ALOC2 | Allenrolfea occidentalis | 34–68 | – | ||
| fourwing saltbush | ATCA2 | Atriplex canescens | 34–68 | – | ||
| water jacket | LYAN | Lycium andersonii | 34–68 | – | ||
| Arizona desert-thorn | LYEX | Lycium exsertum | 34–68 | – | ||
| Torrey wolfberry | LYTO | Lycium torreyi | 34–68 | – | ||
| mesquite | PRJU3 | Prosopis juliflora | 34–68 | – | ||
| seepweed | SUAED | Suaeda | 34–68 | – | ||
| 6 | Succulents | 17–34 | ||||
| Engelmann's hedgehog cactus | ECEN | Echinocereus engelmannii | 17–34 | – | ||
| candy barrelcactus | FEWI | Ferocactus wislizeni | 17–34 | – | ||
Interpretations
Animal community
This site produces forage for year-round use by livestock. Salt desert shrub species will provide adequate protein throughout the year, however energy will usually be lacking on this site from Jun-Jan (except when summer rainfall is sufficient to produce a crop of summer annual grasses and forbs). Spring is the main season for shrub growth and production of annual species. Proper use of the shrubs should be no more than 50% of the spring production of leaves and twigs. Water developments are very important on this site and grazing can be controlled by livestock access to water.
The lack of natural water and poor cover limits the value of this site for wildlife habitat. Large areas of this site have no inclusions of washes or bottom sites needed for cover for the larger mammals. Forage diversity is poor; it is mainly a forage site for birds and desert mammals.
Other information
T&E Species: Tumamoc globe berry (Tumamoca macdougalii) and Sonoran pronghorn (Antilocapra Americana Sonoriensis)
Supporting information
Contributors
DGR
Larry D. Ellicott
Steve Barker
Rangeland 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 | S. Cassady |
| Approval date | |
| Composition (Indicators 10 and 12) based on | Annual Production |
Indicators
-
Number and extent of rills:
None present due to high slopes. -
Presence of water flow patterns:
Water flow patterns are common, but discontinuous and empty into mini-playa areas due to low slopes. -
Number and height of erosional pedestals or terracettes:
All shrubs have symmetrical mounds 2-5 inches tall formed by combined action of splash, erosion adn rodents. There are no pedestals on rock or gravel fragments and no terracettes are present. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
60-70% -
Number of gullies and erosion associated with gullies:
none -
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 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; 7.5-10YR6/4 dry, 7.5-10YR4/4 moist, to 5 inches thick -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Canopy 10-15%: 70-80% shrubs, 5% trees, 10-15% succulents. Cover is well dispersed throughout the site. -
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 > winter annuals > trees > summer annuals > succulents = perennial grasses and forbs > crytogamsSub-dominant:
Other:
Additional:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
0-50% canopy mortality; 90-100% perennial grass mortality. -
Average percent litter cover (%) and depth ( in):
Herbaceous litter is not persistent on the site. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
200 lbs/ac unfavorable precipitation; 300 lbs/ac normal years; 400 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), schismus, filaree -
Perennial plant reproductive capability:
Not impaired for shrubs; drought impaired for perennial grasses and forbs.
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