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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 microphylla
Shrub (1) Ambrosia dumosa
(2) Olneya tesotaHerbaceous (1) Muhlenbergia porteri
(2) Pleuraphis rigidaPhysiographic features
This site occurs as gently sloping to undulating uplands and pediments in and around the low desert mountains.
Table 2. Representative physiographic features
Landforms (1) Pediment
Elevation 75 – 1600 ft Slope 1 – 15 % 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 1. Monthly precipitation range
BarLineFigure 2. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
These soils are very shallow and shallow, loamy and slightly calcareous. Soils formed from both slope alluvium and resiuduum. They are underlain by highly weathered granitic and adesitic bedrock. Plant-soil moisture relationships are fair due to limited available water capacity and shallow depth.
Soil mapped on this site include: in SSA-653 Gila Bend-Ajo area MU's Quilotosa GrSL-61 & Vaiva GrXSL-61.Table 4. Representative soil features
Parent material (1) Slope alluvium – granite
(2) Residuum – gneiss
Surface texture (1) Gravelly loam
(2) Very gravelly fine sandy loam
(3) Sandy loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately rapid to rapid Soil depth 4 – 20 in Surface fragment cover <=3" 15 – 45 % Surface fragment cover >3" 3 – 10 % Available water capacity
(0-40in)0.32 – 2.2 in Calcium carbonate equivalent
(0-40in)1 – 10 % Electrical conductivity
(0-40in)0 – 1 mmhos/cm 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)15 – 45 % Subsurface fragment volume >3"
(Depth not specified)3 – 10 % 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 desert shrubs and trees with a sparse understory of perennial grasses and perennial forbs.
As the site deteriorates from lack of management, the palatable shrubs decline and are replaced by creosotebush, cacti and other unpalatable invader shrubs.Figure 3. 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 140 160 180 Tree 30 40 50 Forb 20 25 30 Grass/Grasslike 10 20 30 Total 200 245 290 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 10–20 bush muhly MUPO2 Muhlenbergia porteri 5–10 – big galleta PLRI3 Pleuraphis rigida 5–10 – threeawn ARIST Aristida 3–5 – 2 Annual Grasses 2–10 sixweeks fescue VUOC Vulpia octoflora 0–5 – low woollygrass DAPU7 Dasyochloa pulchella 0–4 – sixweeks threeawn ARAD Aristida adscensionis 0–2 – needle grama BOAR Bouteloua aristidoides 0–2 – sixweeks grama BOBA2 Bouteloua barbata 0–2 – Forb3 Perennial Forbs 10–20 cottongrass ERIOP Eriophorum 2–5 – Parry's false prairie-clover MAPA7 Marina parryi 2–5 – desert globemallow SPAM2 Sphaeralcea ambigua 1–5 – spurge EUPHO Euphorbia 1–3 – trailing windmills ALIN Allionia incarnata 1–3 – desert trumpet ERIN4 Eriogonum inflatum 1–3 – 4 Annual Forbs 2–10 desert Indianwheat PLOV Plantago ovata 0–5 – velvet turtleback PSRA Psathyrotes ramosissima 0–1 – New Mexico silverbush ARNE2 Argythamnia neomexicana 0–1 – brittle spineflower CHBR Chorizanthe brevicornu 0–1 – devil's spineflower CHRI Chorizanthe rigida 0–1 – Esteve's pincushion CHST Chaenactis stevioides 0–1 – cryptantha CRYPT Cryptantha 0–1 – hairy prairie clover DAMO Dalea mollis 0–1 – American wild carrot DAPU3 Daucus pusillus 0–1 – flatcrown buckwheat ERDE6 Eriogonum deflexum 0–1 – pepperweed LEPID Lepidium 0–1 – foothill deervetch LOHU2 Lotus humistratus 0–1 – strigose bird's-foot trefoil LOSTT Lotus strigosus var. tomentellus 0–1 – Coulter's lupine LUSP2 Lupinus sparsiflorus 0–1 – phacelia PHACE Phacelia 0–1 – Shrub/Vine5 Dominant Shrubs 70–90 burrobush AMDU2 Ambrosia dumosa 40–60 – desert ironwood OLTE Olneya tesota 20–30 – 6 Misc. Shrubs 35–60 San Felipe dogweed ADPO Adenophyllum porophylloides 2–5 – triangle bur ragweed AMDE4 Ambrosia deltoidea 3–5 – narrowleaf silverbush ARLA12 Argythamnia lanceolata 3–5 – brittlebush ENFA Encelia farinosa 3–5 – jointfir EPHED Ephedra 3–5 – California fagonbush FALA Fagonia laevis 3–5 – slender janusia JAGR Janusia gracilis 3–5 – littleleaf ratany KRER Krameria erecta 3–5 – white ratany KRGR Krameria grayi 3–5 – creosote bush LATRT Larrea tridentata var. tridentata 3–5 – desert-thorn LYCIU Lycium 2–5 – slender poreleaf POGR5 Porophyllum gracile 3–5 – American threefold TRCA8 Trixis californica 2–4 – sweetbush BEJU Bebbia juncea 2–4 – 7 Succulents 2–10 saguaro CAGI10 Carnegiea gigantea 1–2 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 1–2 – candy barrelcactus FEWI Ferocactus wislizeni 0–1 – ocotillo FOSP2 Fouquieria splendens 0–1 – Graham's nipple cactus MAGR9 Mammillaria grahamii 0–1 – buckhorn cholla CYACA2 Cylindropuntia acanthocarpa var. acanthocarpa 0–1 – teddybear cholla CYBI9 Cylindropuntia bigelovii 0–1 – Wiggins' cholla CYEC3 Cylindropuntia echinocarpa 0–1 – branched pencil cholla CYRA9 Cylindropuntia ramosissima 0–1 – Tree8 Tree 30–50 yellow paloverde PAMI5 Parkinsonia microphylla 30–50 – Interpretations
Animal community
Being nearly level and associated with steep, rough desert hills, this site if often overused. Adequate water development and fencing, together with the hills, will permit use of greater numbers of animals for shorter periods of time. This will help eliminate overuse of the site and force livestock to use steeper slopes.
Lack of natural water and scanty cover limit the value of the site for wildlife habitat. Forage diversity is good, however, and the site is associated with small canyons that provide needed cover. Water developments are very important to wildlife species in these areas.Recreational uses
This site is located on gently sloping to rolling uplands and pediments in and around the desert mountains. A mixture of an understory of desert shrubs and grass and a good overstory of desert trees enhances the aesthetics of this site. Very few days in the fall, winter or spring are too uncomfortable to enjoy outdoor activities, however, Jun-Aug after lunch heat restricts activity. Horseback riding, wildlife observation, hunting, hiking, photography, camping and picnicking are activities suited to this site.
Supporting information
Type locality
Location 1: Maricopa County, AZ General legal description Arnold Ranch - North end of Buckeye Hills. 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) Contact for lead author Date Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
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Presence of water flow patterns:
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Number and height of erosional pedestals or terracettes:
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Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
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Number of gullies and erosion associated with gullies:
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Extent of wind scoured, blowouts and/or depositional areas:
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Amount of litter movement (describe size and distance expected to travel):
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Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
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Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
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Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
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Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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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:
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):
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Average percent litter cover (%) and depth ( in):
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Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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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:
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Perennial plant reproductive capability:
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PrintThe Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.
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