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Conservation Service
Ecological site R040XA124AZ
Loamy Bottom, Woodland
10"-13" p.z.
Last updated: 10/17/2024
Accessed: 08/17/2026
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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
Major Land Resource Area (MLRA) 40 is the portion of Sonoran Desert that extends from northwest Mexico into southwestern Arizona and southeastern California. This MLRA is hot desert characterized by bimodal precipitation coupled with hot summers and mild winters. These conditions give rise to a rich biological diversity visually dominated by columnar cactus (saguaro) and leguminous trees (palo verde). 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 basin sediments are combinations of fluvial, lacustrine, colluvial and alluvial deposits.
LRU notes
Land Resource Unit (LRU) 40-1, Upper Sonoran Desert, is characterized by desert scrub vegetation with no desert pavement present. Trees grow on uplands as well as in washes and on hillslopes. Elevations range from 2000 to 3800 feet, and precipitation averages 10 to 13 inches per year. Vegetation includes saguaro, palo verde, mesquite, creosotebush, triangle bursage, prickly pear, cholla, limberbush, wolfberry, bush muhly, threeawns, ocotillo, and globe mallow. The soil temperature regime is thermic and the soil moisture regime is typic aridic.
Classification relationships
USDA-NRCS Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin: Western Range and Irrigated Region D Major Land Resource Area 40 - Sonoran Basin and Range Land Resource Unit 1 - Upper Sonoran Desert Ecological Site Loamy Bottom, Woodland, 10"-13" p.z.
U.S. Environmental Protection Agency, Ecological Regions of North America: Level I, Region 10 North American Deserts Level II, 10.2 Warm Deserts Level III, Ecoregion 81, Sonoran Basin and Range Level IV, 81l, 81n, 81o
USDA-USFS Ecological Subregions: Sections of the Conterminous United States Section 322 American Semidesert and Desert Province Section 322B, Sonoran DesertEcological site concept
Loamy Bottom, Woodland, 10"-13" p.z., occurs in a bottom position, receiving both rainfall and run-on moisture. The water table is available to the plant community. Soils do not have redoximorphic features within 80" of surface.
Associated sites
R040XA125AZ Sandy Bottom, Woodland 10"-13" p.z.
adjacent water flow channel, soils with redox features
R040XA112AZ Loamy Swale 10"-13" p.z.
non-saline bottom site without permanent, deep, water table; often associated adjacent opposite water channel
Similar sites
F040XB214AZ Loamy Bottom, Woodland 7"-10" p.z.
Elevations 1,200' - 2,000', lower precipitation, soil hyperthermic
F040XC328AZ Loamy Bottom, Woodland 3"-7" p.z.
Elevations 300' - 1,200', lower precipitation, soil hyperthermic
Table 1. Dominant plant species
Tree (1) Prosopis velutina
Shrub Not specified
Herbaceous (1) Sporobolus wrightii
Physiographic features
This site occurs on stream terraces of major drainageways. It does not experience regular overbank flooding. Some extra moisture may be received from valley side channel flooding. Water table depths are estimated to range from 10 to 50 feet. Stream channels are deeply entrenched.
Table 2. Representative physiographic features
Landforms (1) Stream terrace
Flooding duration Extremely brief (0.1 to 4 hours) to brief (2 to 7 days) Flooding frequency None to rare Ponding duration Very brief (4 to 48 hours) to brief (2 to 7 days) Ponding frequency None to rare Elevation 2000 – 3800 ft Slope 0 – 2 % Aspect Aspect is not a significant factor Climatic features
Annual precipitation ranges from 10 to 13 inches in the southern part of this LRU, with elevations between 1900 and 3200 feet. Annual precipitation in the northern part ranges from 11 to 14 inches, with elevations between 2000 and 3800 feet. Rainfall ratios range from 40:60 (winter:summer) in the southern part, 50:50 in the central portion, and 60:40 in the northern part.
Overall, average annual rainfall is variable, but increases in variability from east to west across the region. For long-term precipitation data, the coefficient of variation, the ratio of the standard deviation to the mean expressed as a percentage, increases from 29% at Tucson (east) to 36% at Carefree (west).
Rainfall intensity differs between rainfall seasons. Winter frontal storms develop in the Pacific Ocean and Gulf of California, producing widespread, low-intensity and long duration precipitation events. Snowfall is rare and seldom last for more than a few hours. During summer months (July-September), atmospheric activity in the Gulf of Mexico produces convective thunderstorms of short duration, usually less than 30 minutes, but of moderate to heavy intensity. May and June are the driest months of the year. Humidity is generally very low.
Winter temperatures are mild, with only a few days of freezing temperatures overnight. Summer temperatures are warm to hot, with several days in June and July exceeding 105°F.
Spring and the summer growing seasons are equally important for perennial grass, forb and shrub growth. With above average precipitation, cool and warm season annual forbs and grasses can be common in their respective seasons. Perennial forage species can remain green throughout the year with sufficient available moisture.Table 3 Representative climatic features
Frost-free period (average) 270 days Freeze-free period (average) Precipitation total (average) 10 in BarLineFigure 1. Monthly precipitation range
BarLineFigure 2. Monthly average minimum and maximum temperature
">Influencing water features
There are no water features associated with this site.
Soil features
These are young soils formed in loamy or silty alluvium of mixed origin. Soils are deep, well drained and may be calcareous or slightly saline, and may contain 0%-5% gypsum. Plant-soil moisture relationships are excellent for deep rooted trees due to a deep ground water table.
Table 4. Representative soil features
Surface texture (1) Fine sandy loam
(2) Loam
(3) Silt loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderate to moderately slow Soil depth 60 in Surface fragment cover <=3" 0 – 10 % Surface fragment cover >3" 0 – 1 % Available water capacity
(0-40in)5.8 – 10.8 in Calcium carbonate equivalent
(0-40in)0 – 10 % Electrical conductivity
(0-40in)0 – 4 mmhos/cm Sodium adsorption ratio
(0-40in)0 – 13 Soil reaction (1:1 water)
(0-40in)7 – 8.2 Subsurface fragment volume <=3"
(Depth not specified)0 – 5 % Ecological dynamics
Loamy Bottom, Woodland, 10-13” p.z. supports a mixed plant community, with an overstory of mesquite and an understory of shrubs, perennial grasses and forbs. Leaf-out for mesquite occurs midspring, after the last frost, produces flowers in late spring or early summer, and mature fruits begin dropping by July. The trees lose their leaves with the first hard frost. The aspect is deciduous woodland.
The site is very susceptible to channel and streambank erosion. Drainageways are deeply entrenched and, if streamside vegetation is disturbed, bank cutting can greatly increase. If the mesquite overstory is reduced, shrub cover will readily expand and become dominant in the plant community. Herbaceous understory density varies with varying canopy cover. Mesquite canopy cover ranges from 30%–65%. Trees can reach maximum size and height on the site. Excessive groundwater pumping can, over time, lower water tables beyond the reach of tree roots and cause extensive tree loss. Tree species vigorously sprout after a fire or manual cutting. Natural fires may have been important in maintaining herbaceous understories. Saltcedar can invade and dominate following disturbance of the native tree cover. Bermudagrass, Johnson grass, foxtail barley and London rocket are introduced species commonly found on this site.State and transition model
Custom diagramStandard diagram
Figure 3. Loamy Bottom, Woodland STM
Figure 4. Loamy Bottom, woodland, 10-13" p.z. STM Legend
More interactive model formats are also available. View Interactive Models
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 1
Mesquite Bosque, Native StateCommunity 1.1
Mesquite, Native Community (Reference)Mesquite dominates the reference plant community with a mixed understory.
Figure 5. 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)Tree 300 475 650 Shrub/Vine 350 400 450 Grass/Grasslike 250 275 300 Forb 200 225 250 Total 1100 1375 1650 State 2
Mesquite Bosque, Exotics StateMesquite canopy intact, and groundwater table within normal range. Non-native annual forbs and grasses, such as London rocket and foxtail barley, dominate the understory. Shrubs and succulents are sparsely present. No flooding occurs.
State 3
Abandoned Farmland StateMesquite bosque absent, and groundwater table within normal range. Initially, native annual forbs and grasses occupy the site, with some patches of non-native annuals. With time, desert broom, greythorn and other shrubs come to dominate the community, with patches of perennial grasses occurring in depressions.
State 4
Mesquite Scrubland StateWater table depleted. Mesquite bosque has altered to a shrubby aspect with a 5%-20% canopy, intermingled with greythorn and other large shrubs.
State 5
Non-Native Woodland StateSaltcedar dominates, becoming an impenetrable thicket.
Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 28–41 Arizona cottontop DICA8 Digitaria californica 28–41 – bush muhly MUPO2 Muhlenbergia porteri 28–41 – whiplash pappusgrass PAVA2 Pappophorum vaginatum 28–41 – plains bristlegrass SEVU2 Setaria vulpiseta 28–41 – spike dropseed SPCO4 Sporobolus contractus 28–41 – big sacaton SPWR2 Sporobolus wrightii 28–41 – 2 14–28 Santa Rita threeawn ARCAG Aristida californica var. glabrata 14–28 – Havard's threeawn ARHA3 Aristida havardii 14–28 – purple threeawn ARPU9 Aristida purpurea 14–28 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 14–28 – spidergrass ARTE3 Aristida ternipes 14–28 – low woollygrass DAPU7 Dasyochloa pulchella 14–28 – saltgrass DISP Distichlis spicata 14–28 – squirreltail ELELE Elymus elymoides ssp. elymoides 14–28 – vine mesquite PAOB Panicum obtusum 14–28 – tobosagrass PLMU3 Pleuraphis mutica 14–28 – cane bluestem BOBA3 Bothriochloa barbinodis 14–28 – sand dropseed SPCR Sporobolus cryptandrus 14–28 – sideoats grama BOCU Bouteloua curtipendula 14–28 – slim tridens TRMU Tridens muticus 14–28 – 3 28–41 prairie threeawn AROL Aristida oligantha 28–41 – needle grama BOAR Bouteloua aristidoides 28–41 – sixweeks grama BOBA2 Bouteloua barbata 28–41 – Rothrock's grama BORO2 Bouteloua rothrockii 28–41 – Arizona brome BRAR4 Bromus arizonicus 28–41 – brome BROMU Bromus 28–41 – feather fingergrass CHVI4 Chloris virgata 28–41 – bearded cupgrass ERAR5 Eriochloa aristata 28–41 – canyon cupgrass ERLE7 Eriochloa lemmonii 28–41 – desert lovegrass ERPEM Eragrostis pectinacea var. miserrima 28–41 – tufted lovegrass ERPEP2 Eragrostis pectinacea var. pectinacea 28–41 – little barley HOPU Hordeum pusillum 28–41 – Mexican sprangletop LEFUU Leptochloa fusca ssp. uninervia 28–41 – mucronate sprangeltop LEPAB Leptochloa panicea ssp. brachiata 28–41 – delicate muhly MUFR Muhlenbergia fragilis 28–41 – littleseed muhly MUMI Muhlenbergia microsperma 28–41 – witchgrass PACA6 Panicum capillare 28–41 – Bigelow's bluegrass POBI Poa bigelovii 28–41 – Arizona signalgrass URAR Urochloa arizonica 28–41 – sixweeks fescue VUOC Vulpia octoflora 28–41 – Forb4 2–11 bigseed alfalfa dodder CUIN Cuscuta indecora 2–11 – mesquite mistletoe PHCA8 Phoradendron californicum 2–11 – 5 23–34 dwarf desertpeony ACNA2 Acourtia nana 23–34 – wheelscale saltbush ATEL Atriplex elegans 23–34 – Wright's saltbush ATWR Atriplex wrightii 23–34 – hedge bamboo BAMU2 Bambusa multiplex 23–34 – New Mexico thistle CINE Cirsium neomexicanum 23–34 – fingerleaf gourd CUDI Cucurbita digitata 23–34 – Missouri gourd CUFO Cucurbita foetidissima 23–34 – coyote gourd CUPA Cucurbita palmata 23–34 – desert thorn-apple DADI2 Datura discolor 23–34 – pricklyburr DAIN2 Datura inoxia 23–34 – Indian rushpea HOGL2 Hoffmannseggia glauca 23–34 – redstar IPCO3 Ipomoea coccinea 23–34 – Gila manroot MAGI Marah gilensis 23–34 – lacy tansyaster MAPIP4 Machaeranthera pinnatifida ssp. pinnatifida var. pinnatifida 23–34 – desert tobacco NIOBO Nicotiana obtusifolia var. obtusifolia 23–34 – Mexican passionflower PAME2 Passiflora mexicana 23–34 – doubleclaw PRPA2 Proboscidea parviflora 23–34 – canaigre dock RUHY Rumex hymenosepalus 23–34 – silverleaf nightshade SOEL Solanum elaeagnifolium 23–34 – 6 23–34 brownfoot ACWR5 Acourtia wrightii 23–34 – trailing windmills ALIN Allionia incarnata 23–34 – weakleaf bur ragweed AMCO3 Ambrosia confertiflora 23–34 – carelessweed AMPA Amaranthus palmeri 23–34 – bristly fiddleneck AMTE3 Amsinckia tessellata 23–34 – rockcress ARABI Arabidopsis 23–34 – milkvetch ASTRA Astragalus 23–34 – scarlet spiderling BOCO Boerhavia coccinea 23–34 – Coulter's spiderling BOCO2 Boerhavia coulteri 23–34 – hoary bowlesia BOIN3 Bowlesia incana 23–34 – Arizona wrightwort CAAR7 Carlowrightia arizonica 23–34 – whitemargin sandmat CHAL11 Chamaesyce albomarginata 23–34 – goosefoot CHENO Chenopodium 23–34 – hyssopleaf sandmat CHHY3 Chamaesyce hyssopifolia 23–34 – cryptantha CRYPT Cryptantha 23–34 – hairy prairie clover DAMO Dalea mollis 23–34 – American wild carrot DAPU3 Daucus pusillus 23–34 – western tansymustard DEPI Descurainia pinnata 23–34 – Palmer's spectaclepod DICA31 Dimorphocarpa candicans 23–34 – flatcrown buckwheat ERDE6 Eriogonum deflexum 23–34 – miniature woollystar ERDI2 Eriastrum diffusum 23–34 – buckwheat ERIOG Eriogonum 23–34 – California poppy ESCAM Eschscholzia californica ssp. mexicana 23–34 – Mexican fireplant EUHE4 Euphorbia heterophylla 23–34 – hairy desertsunflower GECA2 Geraea canescens 23–34 – redstar IPCO3 Ipomoea coccinea 23–34 – Arizona poppy KAGR Kallstroemia grandiflora 23–34 – Gordon's bladderpod LEGO Lesquerella gordonii 23–34 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 23–34 – Coulter's lupine LUSP2 Lupinus sparsiflorus 23–34 – lacy tansyaster MAPIP4 Machaeranthera pinnatifida ssp. pinnatifida var. pinnatifida 23–34 – Nuttall's povertyweed MONU Monolepis nuttalliana 23–34 – glandular threadplant NEGL Nemacladus glanduliferus 23–34 – Florida pellitory PAFL3 Parietaria floridana 23–34 – manybristle chinchweed PEPA2 Pectis papposa 23–34 – phacelia PHACE Phacelia 23–34 – desert Indianwheat PLOV Plantago ovata 23–34 – purslane PORTU Portulaca 23–34 – sage SALVI Salvia 23–34 – sleepy silene SIAN2 Silene antirrhina 23–34 – desert globemallow SPAM2 Sphaeralcea ambigua 23–34 – scarlet globemallow SPCO Sphaeralcea coccinea 23–34 – woollyhead neststraw STMI2 Stylocline micropoides 23–34 – brownplume wirelettuce STPA4 Stephanomeria pauciflora 23–34 – sand fringepod THCU Thysanocarpus curvipes 23–34 – woolly tidestromia TILA2 Tidestromia lanuginosa 23–34 – Shrub/Vine7 100–140 fourwing saltbush ATCA2 Atriplex canescens 100–140 – Palmer's cock's comb CEPA5 Celosia palmeri 100–140 – Drummond's clematis CLDR Clematis drummondii 100–140 – western white clematis CLLI2 Clematis ligusticifolia 100–140 – longleaf jointfir EPTR Ephedra trifurca 100–140 – water jacket LYAN Lycium andersonii 100–140 – desert-thorn LYCIU Lycium 100–140 – Arizona desert-thorn LYEX Lycium exsertum 100–140 – lotebush ZIOB Ziziphus obtusifolia 100–140 – 8 2–40 whitethorn acacia VACO9 Vachellia constricta 20–40 – iodinebush ALOC2 Allenrolfea occidentalis 20–40 – cattle saltbush ATPO Atriplex polycarpa 20–40 – desertbroom BASA2 Baccharis sarothroides 20–40 – singlewhorl burrobrush HYMO Hymenoclea monogyra 20–40 – alkali goldenbush ISACA2 Isocoma acradenia var. acradenia 20–40 – southern goldenbush ISPL Isocoma pluriflora 20–40 – burroweed ISTE2 Isocoma tenuisecta 20–40 – creosote bush LATRT Larrea tridentata var. tridentata 20–40 – nightblooming cereus PEGRT Peniocereus greggii var. transmontanus 20–40 – soaptree yucca YUEL Yucca elata 20–40 – Tree9 5–24 catclaw acacia SEGR4 Senegalia greggii 5–24 – Jerusalem thorn PAAC3 Parkinsonia aculeata 5–24 – honey mesquite PRGLG Prosopis glandulosa var. glandulosa 5–24 – 10 143–285 velvet mesquite PRVE Prosopis velutina 143–285 – 11 5–24 netleaf hackberry CELAR Celtis laevigata var. reticulata 5–24 – desert willow CHLI2 Chilopsis linearis 5–24 – Jerusalem thorn PAAC3 Parkinsonia aculeata 5–24 – screwbean mesquite PRPU Prosopis pubescens 5–24 – American black elderberry SANIC4 Sambucus nigra ssp. canadensis 5–24 – Interpretations
Animal community
This site produces good quantities of spring annual forbs and grasses prior to canopy leaf-out in April. If summer bean crops are harvested, care should be taken to avoid overgrazing the warm season perennial grasses. Horses should not be grazed when a bean crop exists in the trees or on the ground in the summer rainy season.
This site is extremely important to a variety of wildlife, offering well-wooded habitat adjacent to free water in the streambeds for part or all of the year.Wood products
Fuelwood harvest should not reduce canopy cover to less than 20% to limit an increase in undesirable shrub cover. Coppice sprouts achieve canopy dominance faster if stumps are greater than 30 inches in height. Coppice production cuts should occur every 20 to 30 years. Trees should not be cut near streambanks. There are no soil-site factors limiting wood production.
Supporting information
Type locality
Location 1: Pima County, AZ Township/Range/Section T8S R17E S7 General legal description Tucson FO - San Pedro River - 7B Ranch at Mammoth, SW 1/4 Sec. 7 Location 2: Cochise County, AZ Township/Range/Section T11S R18E S23 General legal description Willcox FO - San Pedro River Location 3: Pinal County, AZ Township/Range/Section T4S R12E S6 General legal description Casa Grande FO - Gila River - 15 Ranch Location 4: Pima County, AZ Township/Range/Section T15S R13E S35 General legal description Sells FO - San Xavier Contributors
Dan Robinett
Larry D. Ellicott
Wilma J RenkenApproval
Kendra Moseley, 10/17/2024
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) Contact for lead author Date 08/17/2026 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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