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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 (1) atriplex polycarpa
Herbaceous (1) Trichloris crinita
(2) Pleuraphis rigidaPhysiographic features
This site occurs as nearly level to gently sloping fan terraces, stream terraces and relict basin floors.
Table 2. Representative physiographic features
Landforms (1) Fan
(2) Stream terrace
(3) Basin floor
Elevation 900 – 2050 ft Slope 0 – 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 BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
Soils are deep, well to somewhat excessively drained, saline and sodic soils. They are sandy to loamy with a surface cap of loamy fine sand to sandy loam. Surface textures can range to fine sandy loam, but in these instances, textural change to a heavier horizon must be greater than 20". Subsurface texture may also be coarse or fine loamy. The plant-soil moisture relationship is fair. These soils take water readily, but water available for plant growth is limited by the saline, sodic conditions. pH ranges from 8.0-9.6.
Soils mapped on this site include: SSA-651 Central Maricopa county MU's Antho-Ac & Lf, Valencia-Vb; SSA-658 Gila River Indian Reservation MU's Lagunita (saline)-22, Redun-28 & 32, Shontik-28 & 32, Vint-19 & 35.
Table 4. Representative soil features
Surface texture (1) Sandy loam
(2) Loamy sand
Family particle size (1) Sandy
Drainage class Well drained to somewhat excessively drained Permeability class Moderately slow to rapid Soil depth 60 in Surface fragment cover <=3" 0 – 5 % Surface fragment cover >3" Not specified Available water capacity
(0-40in)4.8 – 12 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)0 – 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 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 ben 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 native plant community on this site is dominated by salt tolerant shrubs. Winter and summer annual forbs and grasses are well represented on this site. Perennial grasses and forbs were present in minor amounts in the potential vegetative community.
With severe disturbance (such as fire or heavy, continuous grazing) the saltbush species are replaced by annual grasses and forbs. Loss of shrub cover can result in accelerated water and wind erosion. The Atriplex spp. are very sensitibe to summer fires on this range site.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 280 310 340 Forb 20 50 80 Grass/Grasslike 20 30 40 Total 320 390 460 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 0–2 Havard's threeawn ARHA3 Aristida havardii 0–2 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 0–2 – spidergrass ARTE3 Aristida ternipes 0–2 – bush muhly MUPO2 Muhlenbergia porteri 0–2 – big galleta PLRI3 Pleuraphis rigida 0–2 – spike dropseed SPCO4 Sporobolus contractus 0–2 – 2 0–2 sixweeks threeawn ARAD Aristida adscensionis 0–2 – prairie threeawn AROL Aristida oligantha 0–2 – needle grama BOAR Bouteloua aristidoides 0–2 – sixweeks grama BOBA2 Bouteloua barbata 0–2 – Rothrock's grama BORO2 Bouteloua rothrockii 0–2 – Arizona brome BRAR4 Bromus arizonicus 0–2 – feather fingergrass CHVI4 Chloris virgata 0–2 – spreading fleabane ERDI4 Erigeron divergens 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 – Bigelow's bluegrass POBI Poa bigelovii 0–2 – sixweeks fescue VUOC Vulpia octoflora 0–2 – Forb3 5–20 desert Indianwheat PLOV Plantago ovata 5–20 – 4 5–60 weakleaf bur ragweed AMCO3 Ambrosia confertiflora 0–1 – fringed amaranth AMFI Amaranthus fimbriatus 0–1 – common fiddleneck AMMEI2 Amsinckia menziesii var. intermedia 0–1 – wheelscale saltbush ATEL Atriplex elegans 0–1 – wheelscale saltbush ATELF Atriplex elegans var. fasciculata 0–1 – hoary bowlesia BOIN3 Bowlesia incana 0–1 – yellow tackstem CAPA7 Calycoseris parryi 0–1 – white tackstem CAWR Calycoseris wrightii 0–1 – whitemargin sandmat CHAL11 Chamaesyce albomarginata 0–1 – aridland goosefoot CHDE Chenopodium desiccatum 0–1 – cryptantha CRYPT Cryptantha 0–1 – American wild carrot DAPU3 Daucus pusillus 0–1 – miniature woollystar ERDI2 Eriastrum diffusum 0–1 – Gordon's bladderpod LEGO Lesquerella gordonii 0–1 – pepperweed LEPID Lepidium 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 – bristly nama NAHI Nama hispidum 0–1 – combseed PECTO Pectocarya 0–1 – phacelia PHACE Phacelia 0–1 – New Mexico plumeseed RANE Rafinesquia neomexicana 0–1 – canaigre dock RUHY Rumex hymenosepalus 0–1 – smooth threadleaf ragwort SEFLM Senecio flaccidus var. monoensis 0–1 – sleepy silene SIAN2 Silene antirrhina 0–1 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 0–1 – woollyhead neststraw STMI2 Stylocline micropoides 0–1 – woolly tidestromia TILA2 Tidestromia lanuginosa 0–1 – Shrub/Vine5 200–240 cattle saltbush ATPO Atriplex polycarpa 200–240 – 6 20–60 fourwing saltbush ATCA2 Atriplex canescens 16–47 – water jacket LYAN Lycium andersonii 16–47 – velvet mesquite PRVE Prosopis velutina 16–47 – 7 20–40 burrobush AMDU2 Ambrosia dumosa 16–31 – thinleaf fourwing saltbush ATCAL4 Atriplex canescens var. linearis 16–31 – creosote bush LATRT Larrea tridentata var. tridentata 16–31 – Arizona desert-thorn LYEX Lycium exsertum 16–31 – Torrey wolfberry LYTO Lycium torreyi 16–31 – greasewood SAVE4 Sarcobatus vermiculatus 16–31 – seepweed SUAED Suaeda 16–31 – 8 Succulents 5–20 Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 3–16 – candy barrelcactus FEWI Ferocactus wislizeni 3–16 – 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 from Jun-Jan (except when summer rains are sufficient to produce a crop of summer annual grasses and forbs). Spring is the main season for plant growth and production of annual species. Proper use of the shrub species should be no more than 50% of the spring production of twigs and leaves. Water developments are very important. Grazing can be controlled by controlling livestock access to water.
Lack of natural water and poor cover limits the value of this site as wildlife habitat. Large areas of this site have no inclusions of washes or bottom sites to provide the needed cover for larger desert animals. Forage diversity is fair. The site is mainly home to small desert animals and a forage area for birds.Other information
T&E Species: Tumamoc globe berry (Tumamoca macdougalii) and Sonoran pronghorn (Antilocapra Americana sonoriensis)
Supporting information
Contributors
Dan Robinett
DGR
Larry D. EllicottRangeland 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:
None present due to low slopes. -
Presence of water flow patterns:
Water flow patterns are uncommon 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 and 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 mdoerate 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 and 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 > crytogams (in El Nino years, the production of winter annuals can exceed all other plants.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):
0-50% canopy mortality. 90-100% mortality of perennial grasses. -
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 precipitation; 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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