Natural Resources
Conservation Service
Ecological site R040XB203AZ
Clayey Swale 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 |
(1) Parkinsonia florida |
|---|---|
| Shrub |
(1) Prosopis velutina |
| Herbaceous |
(1) Pleuraphis mutica |
Physiographic features
This site occurs on floodplains and alluvial fans. Slopes are from 0 to 2%. This site benefits on a regular basis from extra moisture received as runoff from adjacent uplands. Elevations range from 1100 to 2200 feet.
Table 2. Representative physiographic features
| Landforms |
(1)
Flood plain
(2) Alluvial fan |
|---|---|
| Elevation | 335 – 671 m |
| Slope | 0 – 2% |
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) | 254 mm |
Figure 2. Monthly precipitation range
Figure 3. Monthly average minimum and maximum temperature
Influencing water features
Soil features
These are deep soils on clayey alluvium of mixed origin. They are dark colored and have high shrink-swell potentials. Cracking and churning cause very rough surfaces. Plant-soil moisture relationships are very good.
Soils mapped on this site include: in
SSA-645 Aguila-Carefree area MU Gadsden-53;
SSA-651 Central Maricopa County MU's Gadsden-Gc & Vecont-Vf;
SSA-653 Gila Bend-Ajo area MU Gadsden-24;
SSA-659 Western Pinal County MU's Cashion-5, Gadsden-20, Ginland-23 & Pirner-36;
SSA-661 Eastern Pinal-Southern Gila Counties MU's Gadsden-355, Cashion-370 & Contine-830;
SSA-669 Eastern Pima County MU Vecont-83;
SSA-703 Gadsden-24, Ginland-26 & Vecont-61.
Table 4. Representative soil features
| Surface texture |
(1) Clay loam (2) Silty clay loam (3) Clay |
|---|---|
| Family particle size |
(1) Clayey |
| Drainage class | Well drained |
| Permeability class | Very slow |
| Soil depth | 152 cm |
| Surface fragment cover <=3" | 0% |
| Surface fragment cover >3" | 0% |
| Available water capacity (0-101.6cm) |
21.34 – 27.43 cm |
| Calcium carbonate equivalent (0-101.6cm) |
1 – 10% |
| Electrical conductivity (0-101.6cm) |
0 – 2 mmhos/cm |
| Sodium adsorption ratio (0-101.6cm) |
0 |
| Soil reaction (1:1 water) (0-101.6cm) |
7.9 – 8.4 |
| Subsurface fragment volume <=3" (Depth not specified) |
0% |
| Subsurface fragment volume >3" (Depth not specified) |
0% |
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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Ecosystem states
State 1 submodel, plant communities
State 1
Historical Climax Plant Community
Community 1.1
Historical Climax Plant Community
The potential plant community on this site is dominated by tobosa grass. Annual forbs and grasses are common. Shrubs are not common. Ths aspect is open grassland. With continuous, heavy grazing the cover of tobosa grass is depleted. The site is very suscepetible to gully erosion once the perennial grass cover has been removed. Gully formation acts to rapidly drain flood waters from the site. This reduces potential productivity and allows shrubs like; mesquite, whitethorn, jimmyweed and goldenweed to invade and increase.
Figure 4. 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 | 717 | – | 807 |
| Forb | 45 | – | 90 |
| Shrub/Vine | 18 | – | 45 |
| Tree | 18 | – | 45 |
| Total | 798 | – | 987 |
Additional community tables
Table 6. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (kg/hectare) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Grass/Grasslike
|
||||||
| 1 | 534–610 | |||||
| tobosagrass | PLMU3 | Pleuraphis mutica | 534–610 | – | ||
| 2 | 8–38 | |||||
| purple threeawn | ARPU9 | Aristida purpurea | 8–38 | – | ||
| Parish's threeawn | ARPUP5 | Aristida purpurea var. parishii | 8–38 | – | ||
| Wright's threeawn | ARPUW | Aristida purpurea var. wrightii | 8–38 | – | ||
| spidergrass | ARTE3 | Aristida ternipes | 8–38 | – | ||
| spidergrass | ARTEG | Aristida ternipes var. gentilis | 8–38 | – | ||
| bush muhly | MUPO2 | Muhlenbergia porteri | 8–38 | – | ||
| vine mesquite | PAOB | Panicum obtusum | 8–38 | – | ||
| big galleta | PLRI3 | Pleuraphis rigida | 8–38 | – | ||
| 3 | 38–76 | |||||
| sixweeks threeawn | ARAD | Aristida adscensionis | 38–76 | – | ||
| needle grama | BOAR | Bouteloua aristidoides | 38–76 | – | ||
| sixweeks grama | BOBA2 | Bouteloua barbata | 38–76 | – | ||
| Rothrock's grama | BORO2 | Bouteloua rothrockii | 38–76 | – | ||
| Arizona brome | BRAR4 | Bromus arizonicus | 38–76 | – | ||
| feather fingergrass | CHVI4 | Chloris virgata | 38–76 | – | ||
| canyon cupgrass | ERLE7 | Eriochloa lemmonii | 38–76 | – | ||
| Arizona barley | HOAR | Hordeum arizonicum | 38–76 | – | ||
| little barley | HOPU | Hordeum pusillum | 38–76 | – | ||
| bearded sprangletop | LEFUF | Leptochloa fusca ssp. fascicularis | 38–76 | – | ||
| mucronate sprangletop | LEPA6 | Leptochloa panicea | 38–76 | – | ||
| sticky sprangletop | LEVI5 | Leptochloa viscida | 38–76 | – | ||
| delicate muhly | MUFR | Muhlenbergia fragilis | 38–76 | – | ||
| littleseed muhly | MUMI | Muhlenbergia microsperma | 38–76 | – | ||
| Bigelow's bluegrass | POBI | Poa bigelovii | 38–76 | – | ||
| Arizona signalgrass | URAR | Urochloa arizonica | 38–76 | – | ||
| Eastwood fescue | VUMIC | Vulpia microstachys var. ciliata | 38–76 | – | ||
| Pacific fescue | VUMIP | Vulpia microstachys var. pauciflora | 38–76 | – | ||
| sixweeks fescue | VUOC | Vulpia octoflora | 38–76 | – | ||
| 4 | 0–1 | |||||
| Alga | 2ALGA | Alga | 0–1 | – | ||
| Fungus | 2FUNGI | Fungus | 0–1 | – | ||
| Moss | 2MOSS | Moss | 0–1 | – | ||
|
Forb
|
||||||
| 5 | 45–90 | |||||
| dwarf desertpeony | ACNA2 | Acourtia nana | 0–1 | – | ||
| weakleaf bur ragweed | AMCO3 | Ambrosia confertiflora | 0–1 | – | ||
| common fiddleneck | AMMEI2 | Amsinckia menziesii var. intermedia | 0–1 | – | ||
| carelessweed | AMPA | Amaranthus palmeri | 0–1 | – | ||
| bristly fiddleneck | AMTE3 | Amsinckia tessellata | 0–1 | – | ||
| tuber anemone | ANTU | Anemone tuberosa | 0–1 | – | ||
| milkweed | ASCLE | Asclepias | 0–1 | – | ||
| milkvetch | ASTRA | Astragalus | 0–1 | – | ||
| Coulter's spiderling | BOCO2 | Boerhavia coulteri | 0–1 | – | ||
| hoary bowlesia | BOIN3 | Bowlesia incana | 0–1 | – | ||
| fringed redmaids | CACI2 | Calandrinia ciliata | 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 | – | ||
| brittle spineflower | CHBR | Chorizanthe brevicornu | 0–1 | – | ||
| New Mexico thistle | CINE | Cirsium neomexicanum | 0–1 | – | ||
| sand pygmyweed | CRCO34 | Crassula connata | 0–1 | – | ||
| cryptantha | CRYPT | Cryptantha | 0–1 | – | ||
| fingerleaf gourd | CUDI | Cucurbita digitata | 0–1 | – | ||
| Missouri gourd | CUFO | Cucurbita foetidissima | 0–1 | – | ||
| coyote gourd | CUPA | Cucurbita palmata | 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 | – | ||
| bluedicks | DICA14 | Dichelostemma capitatum | 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 | – | ||
| hairy desertsunflower | GECA2 | Geraea canescens | 0–1 | – | ||
| gilia | GILIA | Gilia | 0–1 | – | ||
| Indian rushpea | HOGL2 | Hoffmannseggia glauca | 0–1 | – | ||
| Arizona poppy | KAGR | Kallstroemia grandiflora | 0–1 | – | ||
| California goldfields | LACA7 | Lasthenia californica | 0–1 | – | ||
| Gordon's bladderpod | LEGO | Lesquerella gordonii | 0–1 | – | ||
| shaggyfruit pepperweed | LELA | Lepidium lasiocarpum | 0–1 | – | ||
| pepperweed | LEPID | Lepidium | 0–1 | – | ||
| Bigelow's linanthus | LIBI2 | Linanthus bigelovii | 0–1 | – | ||
| flax | LINUM | Linum | 0–1 | – | ||
| coastal bird's-foot trefoil | LOSA | Lotus salsuginosus | 0–1 | – | ||
| Arizona lupine | LUAR4 | Lupinus arizonicus | 0–1 | – | ||
| Coulter's lupine | LUSP2 | Lupinus sparsiflorus | 0–1 | – | ||
| Texas bluebonnet | LUSU | Lupinus subcarnosus | 0–1 | – | ||
| disc mayweed | MADI6 | Matricaria discoidea | 0–1 | – | ||
| Nuttall's povertyweed | MONU | Monolepis nuttalliana | 0–1 | – | ||
| bristly nama | NAHI | Nama hispidum | 0–1 | – | ||
| evening primrose | OENOT | Oenothera | 0–1 | – | ||
| lineleaf whitepuff | OLLI | Oligomeris linifolia | 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 | – | ||
| Arizona popcornflower | PLAR | Plagiobothrys arizonicus | 0–1 | – | ||
| desert Indianwheat | PLOV | Plantago ovata | 0–1 | – | ||
| redseed plantain | PLRH | Plantago rhodosperma | 0–1 | – | ||
| desert unicorn-plant | PRAL4 | Proboscidea althaeifolia | 0–1 | – | ||
| New Mexico plumeseed | RANE | Rafinesquia neomexicana | 0–1 | – | ||
| sleepy silene | SIAN2 | Silene antirrhina | 0–1 | – | ||
| tube tongue | SIPHO | Siphonoglossa | 0–1 | – | ||
| desert globemallow | SPAM2 | Sphaeralcea ambigua | 0–1 | – | ||
| Coulter's globemallow | SPCO2 | Sphaeralcea coulteri | 0–1 | – | ||
| woollyhead neststraw | STMI2 | Stylocline micropoides | 0–1 | – | ||
| cutleaf thelypody | THLA | Thelypodium laciniatum | 0–1 | – | ||
| woolly tidestromia | TILA2 | Tidestromia lanuginosa | 0–1 | – | ||
| Louisiana vetch | VILU | Vicia ludoviciana | 0–1 | – | ||
|
Shrub/Vine
|
||||||
| 6 | 0–1 | |||||
| whitemargin sandmat | CHAL11 | Chamaesyce albomarginata | 3–7 | – | ||
| brittle spineflower | CHBR | Chorizanthe brevicornu | 3–7 | – | ||
| hairy prairie clover | DAMO | Dalea mollis | 3–7 | – | ||
| western tansymustard | DEPI | Descurainia pinnata | 3–7 | – | ||
| touristplant | DIWI2 | Dimorphocarpa wislizeni | 3–7 | – | ||
| flatcrown buckwheat | ERDE6 | Eriogonum deflexum | 3–7 | – | ||
| common woolly sunflower | ERLA6 | Eriophyllum lanatum | 3–7 | – | ||
| California poppy | ESCAM | Eschscholzia californica ssp. mexicana | 3–7 | – | ||
| pygmy poppy | ESMI | Eschscholzia minutiflora | 3–7 | – | ||
| flax | LINUM | Linum | 3–7 | – | ||
| Arizona lupine | LUAR4 | Lupinus arizonicus | 3–7 | – | ||
| Coulter's lupine | LUSP2 | Lupinus sparsiflorus | 3–7 | – | ||
| Texas bluebonnet | LUSU | Lupinus subcarnosus | 3–7 | – | ||
| lineleaf whitepuff | OLLI | Oligomeris linifolia | 3–7 | – | ||
| Florida pellitory | PAFL3 | Parietaria floridana | 3–7 | – | ||
| Engelmann's hedgehog cactus | ECEN | Echinocereus engelmannii | 0–1 | – | ||
| candy barrelcactus | FEWI | Ferocactus wislizeni | 0–1 | – | ||
| dollarjoint pricklypear | OPCH | Opuntia chlorotica | 0–1 | – | ||
| limestone adderstongue | OPEN | Ophioglossum engelmannii | 0–1 | – | ||
Interpretations
Animal community
Due to seasonal availability of free water in natural charcos and discontinuous gullies, a long green season and easy accessibility, areas of this site are often overused. Tobosa, the dominant grass, is unpalatable when dry and should be grazed in the spring and summer growing season. Prescribed burning to freshen tobosa should not be used in this MLRA. The plant community is deficient in digestible protein in the fall and winter. Stock ponds constructed on this site should be carefully designed to avoid drying up downstream areas and altering base levels allowing gully formation to occur.
This site is mainly a foraging area for the larger desert mammals. Free water is available in the rainy seasons in natural charcos and discontinuous gullies. Water developments to provide water throughout the year will help some species of wildlife on the site. Being a grassland site, it is home to mainly a variety of small mammals and their predators.
Other information
T&E: Antilocapra Americana sonoriensis
(Sonoran pronghorn)
Supporting information
Type locality
| Location 1: Maricopa County, AZ | |
|---|---|
| Township/Range/Section | T5N R2E S4 |
| General legal description | Phoenix FO - Black Canyon Shooting Range |
| Location 2: Pima County, AZ | |
| Township/Range/Section | T9S R2E S16 |
| General legal description | Sells FO - Headwaters of Vekol Wash |
Contributors
Dan Robinett
Dan Robinett, JN
Larry D. Ellicott
Stephen Cassady
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:
Uncommon. -
Presence of water flow patterns:
Water flow patterns are uncommon, highly variable and a function of upland runoff. Vertic soil properties (high shrink-swell) continually reshape the surface. -
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):
20-60%. Lower values expected in El Nino years. -
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 water shen 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 resistance 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 subgranular blocky with depth; 7.5-10YR5/2 dry, 7.5-10YR3/2 moist, to 20+ inches thick. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Canopy 20-30%; 85-90% perennial grasses, 5-10% annual forbs and grasses, and <2-3% trees and shrubs. 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:
perennial grasses > winter annuals > summer annuals > trees & shrubs > perennial forbs > cryptogamsSub-dominant:
Other:
Additional:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
0-50% canopy mortality -
Average percent litter cover (%) and depth ( in):
Herbaceous 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):
400 lbs/ac unfavorable precipitation; 800 lbs/ac normal precipitation; 1500 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, mesquite -
Perennial plant reproductive capability:
Not impaired for shrubs, drought impaired for perennial grasses and forbs.
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