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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): 041X–Madrean Archipelago
AZ 41.2 – Chihuahuan – Sonoran Desert Shrubs
Elevations range from 2600 to 4000 feet and precipitation ranges from 8 to 12 inches per year. Vegetation includes mesquite, palo verde, catclaw acacia, soaptree yucca, creosotebush, whitethorn, staghorn cholla, desert saltbush, Mormon tea, burroweed, snakeweed, tobosa, black grama, threeawns, bush muhly, dropseed, and burrograss. The soil temperature regime is thermic 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.Associated sites
R041XC312AZ Loamy Bottom 12-16" p.z.
R041XC313AZ Loamy Upland 12"-16" p.z.
R041XC319AZ Sandy Loam Upland 12-16" p.z.
Similar sites
R041XB211AZ Saline Bottom 8-12" p.z.
Table 1. Dominant plant species
Tree Not specified
Shrub (1) atriplex obovata
Herbaceous (1) sporobolus airoides
Physiographic features
This site occurs in the lowest elevations of the Madrean Basin and Range province in southeastern Arizona. It occurs on alluvial fans flanking the Gila and San Simon Rivers. It benefits on a sporadic basis from extra moisture received as runoff from the contributory watershed areas.
Table 2. Representative physiographic features
Landforms (1) Alluvial fan
(2) Flood plain
(3) Flood-plain playa
Flooding duration Very brief (4 to 48 hours) to brief (2 to 7 days) Flooding frequency Occasional to frequent Ponding duration Very brief (4 to 48 hours) to brief (2 to 7 days) Ponding frequency Rare to occasional Elevation 2600 – 4000 ft Slope 0 – 3 % Aspect Aspect is not a significant factor Climatic features
Precipitation ranges from 8-12 inches annually. More than half falls during Jul-Sep in brief, but often heavy, thunderstorms. The rest of the moisture comes as light rain or snow that falls slowly for a day or more, but rarely lasts more than a day. May and June are normally the driest months. Humidity is generally very low.
Temperatures are mild throughout most of the year. Freezing temperatures are common at night Dec-Feb; brief 0 F may be observed some nights. During June, July & August, some days may exceed 100 F.
In years of average or greater winter precipitation, annual grasses and forbs occur abundantly in the interspaces.Table 3 Representative climatic features
Frost-free period (average) 240 days Freeze-free period (average) 0 days Precipitation total (average) 0 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
There are no water features on this site.
Soil features
These soils are of various depth and textures. They have all formed in strongly saline and/or alkaline, basin floor alluvium. Plant-soil moisture relationships are fair to poor due to infrequent flooding.
Soils mapped on this site include: SSA-666 Cochise county Northwest part MU 50 Hantz; SSA-671 Cochise county Douglas-Tombstone part MU 85 Hantz SiL saline-sodic.Table 4. Representative soil features
Surface texture (1) Clay loam
(2) Silty clay loam
(3) Silty clay
Family particle size (1) Clayey
Drainage class Somewhat poorly drained to well drained Permeability class Moderately slow to very slow Soil depth 60 in Surface fragment cover <=3" 0 – 5 % Surface fragment cover >3" 0 – 1 % Available water capacity
(0-40in)3.6 – 6 in Calcium carbonate equivalent
(0-40in)1 – 20 % Electrical conductivity
(0-40in)4 – 20 mmhos/cm Sodium adsorption ratio
(0-40in)6 – 60 Soil reaction (1:1 water)
(0-40in)7.4 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)0 – 5 % Subsurface fragment volume >3"
(Depth not specified)0 – 1 % 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 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 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
Custom diagramStandard diagram
Figure 4. 41-2 Saline Bottom STM Diagram
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 2 submodel, plant communities
State 3 submodel, plant communities
State 4 submodel, plant communities
State 1
ReferenceCommunity 1.1
Savannah (HCPC)The potential plant community is dominated by a warm perennial grass; alkalai sacaton. Scattered trees give the site a savannah appearance. Several species of shrubs and perennial and annual forbs are unique to this site.
This site is not flooded on a regular basis. Production will vary from what rainfall can produce in one year, to several times that when the site floods in another year. In large areas of this site there will be places where water concentrates and larger areas where runoff occurs. Flooding in "El Nino" years will be widespread and of long duration.
As the plant community deteriorates from continuous heavy grazing and/or repeated burning alkalai sacaton can decrease in cover. Mesquite can increase to densities of 20-30 percent canopy without a noticeable decline in grass under-story. Tree size varies with soil texture and depth. Areas of the site flanking the Willcox playa are not subject to gully erosion as base level is controlled by the closed drainage system. However, areas which flank stream floodplains are subject to severe gully erosion if the base level of the stream is lowered and the grass cover is depleted by improper management. Natural fire was a feature of this and helped maintain the shrub free aspect of the potential plant community.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)Grass/Grasslike 406 1000 1750 Forb 6 30 125 Tree 5 10 100 Shrub/Vine 5 20 95 Total 422 1060 2070 Figure 6. Plant community growth curve (percent production by month). AZ4134 , 41.3 12-16" p.z. other sites. Growth begins in the spring, semi-dormancy occurs during the May through June drought, most growth occurs during the summer rains..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 5 10 0 0 30 35 15 5 0 0 Community 1.2
Annual Forbs and GrassesPathway 1.1a
Community 1.1 to 1.2Natural fire controls canopy growth of mesquite and whitethorn acacia. Annual forbs and grasses populate the exposed plant interspaces among alkali sacaton.
Conservation practices
Prescribed Burning Upland Wildlife Habitat Management Prescribed Grazing Pathway 1.2a
Community 1.2 to 1.1In the 10-20 year interval between natural fire events, alkali sacaton resumes dominance of plant community. Mesquite re-sprout after fire to return savannah aspect to landscape.
Conservation practices
Upland Wildlife Habitat Management Prescribed Grazing State 2
Mesquite, native grassCommunity 2.1
Mesquite, native grassMesquite increases in the absence of fire for long periods of time. Alkalai sacaton can maintain good cover with up to 25% canopy of mesquite in occasionally flooded situations.
State 3
Annual grasses and forbsCommunity 3.1
Annual grasses and forbsThis state occurs where the native plant community has been plowed and the site brought under cultivation (irrigated agriculture) and subsequently abandoned. Native and non-native annual forbs and grasses dominate the plant community. Shrubs like desert broom, jimmyweed and burroweed can be present.
State 4
Eroded, w/wo mesquiteCommunity 4.1
Eroded, w/wo mesquiteThis state occurs where the site has been depleted of grass cover either due to cultivation or due to the interactions of fire, drought and continuous grazing. Base level changes of associated stream systems will cause gulling of the site in this condition. Areas of this state around the Willcox playa will not have gullies due to the base level control of the playa, but will have severe sheet and rill erosion due to lack of plant cover, soil compaction and trailing. This state can have moderate to high amounts of mesquite present. Erosion networks cause large amounts of water to be rapidly drained from the site.
Transition T1A
State 1 to 2Long fire-free periods, fire suppression or due to grazing/consumption of fine fuel, allows mesquite unhindered growth.
Transition T1B
State 1 to 3Conversion to and subsequent abdonment of irrigated cultivation.
Restoration pathway R2A
State 2 to 1Returning fire to the ecosytem will not control mesquite in this State. Mechanical or chemical woody species management is needed. Grazing management and prescribed fire will maintain herbaceous community after brush control is applied.
Conservation practices
Brush Management Prescribed Burning Upland Wildlife Habitat Management Prescribed Grazing Transition T2A
State 2 to 3Conversion to and subsequent abdonment of irrigated cultivation.
Transition T2B
State 2 to 4Long-term unmanaged grazing affects soil site stability and hydrologic functioning. Animal trailing and soil surface compaction compound the affect of plant community changes (increased trees/decreased perennial grass community) to increase surface water run-off rather than infiltration.
Transition T3A
State 3 to 4Long-term unmanaged grazing affects soil site stability and hydrologic functioning. Animal trailing and soil surface compaction compound the affect of plant community changes (increased shrub/decreased perennial grass community) to increase surface water run-off rather than infiltration.
Restoration pathway R3A
State 3 to 4No restoration pathway known at this time. Perhaps development of enhanced native seeding techniques will occur.
Conservation practices
Brush Management Mulching Grazing Land Mechanical Treatment Range Planting Recreation Area Improvement Recreation Land Grading and Shaping Upland Wildlife Habitat Management Prescribed Grazing Road/Trail/Landing Closure and Treatment 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 grass 400–1500 alkali sacaton SPAI Sporobolus airoides 400–1500 – 2 Miscellaneous perennial grasses 5–150 big sacaton SPWR2 Sporobolus wrightii 0–75 – saltgrass DISP Distichlis spicata 1–50 – vine mesquite PAOB Panicum obtusum 0–30 – scratchgrass MUAS Muhlenbergia asperifolia 0–25 – creeping muhly MURE Muhlenbergia repens 0–25 – spidergrass ARTE3 Aristida ternipes 0–15 – spidergrass ARTEG Aristida ternipes var. gentilis 0–15 – blue grama BOGR2 Bouteloua gracilis 0–15 – tobosagrass PLMU3 Pleuraphis mutica 0–15 – knotgrass PADI6 Paspalum distichum 0–10 – hairy grama BOHI2 Bouteloua hirsuta 0–10 – Rothrock's grama BORO2 Bouteloua rothrockii 0–10 – sedge CAREX Carex 0–5 – flatsedge CYPER Cyperus 0–5 – Parish's threeawn ARPUP5 Aristida purpurea var. parishii 0–5 – burrograss SCBR2 Scleropogon brevifolius 0–5 – plains bristlegrass SEVU2 Setaria vulpiseta 0–5 – spike dropseed SPCO4 Sporobolus contractus 0–5 – sand dropseed SPCR Sporobolus cryptandrus 0–5 – 3 Annual grasses 1–100 feather fingergrass CHVI4 Chloris virgata 1–25 – prairie threeawn AROL Aristida oligantha 1–25 – needle grama BOAR Bouteloua aristidoides 0–15 – tapertip cupgrass ERACA Eriochloa acuminata var. acuminata 0–15 – mucronate sprangletop LEPA6 Leptochloa panicea 0–15 – sticky sprangletop LEVI5 Leptochloa viscida 0–15 – Mexican sprangletop LEFUU Leptochloa fusca ssp. uninervia 0–10 – Arizona brome BRAR4 Bromus arizonicus 0–5 – tufted lovegrass ERPE Eragrostis pectinacea 0–5 – little barley HOPU Hordeum pusillum 0–5 – sixweeks threeawn ARAD Aristida adscensionis 0–5 – delicate muhly MUFR Muhlenbergia fragilis 0–5 – littleseed muhly MUMI Muhlenbergia microsperma 0–5 – witchgrass PACA6 Panicum capillare 0–5 – Mexican panicgrass PAHI5 Panicum hirticaule 0–5 – Bigelow's bluegrass POBI Poa bigelovii 0–5 – poverty dropseed SPVA Sporobolus vaginiflorus 0–5 – Arizona signalgrass URAR Urochloa arizonica 0–5 – sixweeks fescue VUOC Vulpia octoflora 0–5 – Forb4 Perennial forbs 5–50 fingerleaf gourd CUDI Cucurbita digitata 1–15 – Missouri gourd CUFO Cucurbita foetidissima 0–15 – weakleaf bur ragweed AMCO3 Ambrosia confertiflora 1–15 – alkali marsh aster ALPA14 Almutaster pauciflorus 0–5 – scarlet spiderling BOCO Boerhavia coccinea 0–5 – spiny chloracantha CHSP11 Chloracantha spinosa 0–5 – coyote gourd CUPA Cucurbita palmata 0–5 – beeblossom GAURA Gaura 0–5 – southwestern mock vervain GLGO Glandularia gooddingii 0–5 – small matweed GUDE Guilleminea densa 0–5 – Indian rushpea HOGL2 Hoffmannseggia glauca 0–5 – lacy tansyaster MAPI Machaeranthera pinnatifida 0–5 – camphor pluchea PLCA7 Pluchea camphorata 0–5 – canaigre dock RUHY Rumex hymenosepalus 0–5 – earleaf fanpetals SITR Sida tragiifolia 0–5 – silverleaf nightshade SOEL Solanum elaeagnifolium 0–5 – silky sophora SONU Sophora nuttalliana 0–5 – gooseberryleaf globemallow SPGR2 Sphaeralcea grossulariifolia 0–5 – spear globemallow SPHA Sphaeralcea hastulata 0–5 – dwarf desertpeony ACNA2 Acourtia nana 0–2 – clasping milkweed ASAM Asclepias amplexicaulis 0–1 – 5 Annual forbs 1–75 common sunflower HEAN3 Helianthus annuus 0–50 – common sunflower HEAN3 Helianthus annuus 0–50 – San Pedro matchweed XAGY Xanthocephalum gymnospermoides 0–30 – Nuttall's povertyweed MONU Monolepis nuttalliana 0–30 – salt heliotrope HECU3 Heliotropium curassavicum 0–25 – wheelscale saltbush ATEL Atriplex elegans 0–25 – carelessweed AMPA Amaranthus palmeri 0–25 – wheelscale saltbush ATEL Atriplex elegans 1–25 – Wright's saltbush ATWR Atriplex wrightii 0–25 – salt heliotrope HECU3 Heliotropium curassavicum 0–25 – seaside heliotrope HECUO Heliotropium curassavicum var. oculatum 0–25 – western tansymustard DEPI Descurainia pinnata 1–25 – Nuttall's povertyweed MONU Monolepis nuttalliana 0–25 – San Pedro matchweed XAGY Xanthocephalum gymnospermoides 0–25 – intermediate pepperweed LEVIM Lepidium virginicum var. medium 0–15 – hairy desertsunflower GECA2 Geraea canescens 0–15 – longleaf false goldeneye HELOA2 Heliomeris longifolia var. annua 0–15 – longleaf false goldeneye HELOL Heliomeris longifolia var. longifolia 0–15 – camphorweed HESU3 Heterotheca subaxillaris 0–15 – goosefoot CHENO Chenopodium 0–15 – Wright's saltbush ATWR Atriplex wrightii 0–15 – goosefoot CHENO Chenopodium 0–15 – carelessweed AMPA Amaranthus palmeri 0–15 – bristly fiddleneck AMTE3 Amsinckia tessellata 0–15 – intermediate pepperweed LEVIM Lepidium virginicum var. medium 0–15 – western tansymustard DEPI Descurainia pinnata 0–15 – longleaf false goldeneye HELOA2 Heliomeris longifolia var. annua 0–15 – hairy desertsunflower GECA2 Geraea canescens 0–10 – slender goldenweed MAGR10 Machaeranthera gracilis 0–10 – tanseyleaf tansyaster MATA2 Machaeranthera tanacetifolia 0–10 – golden crownbeard VEEN Verbesina encelioides 0–10 – cryptantha CRYPT Cryptantha 0–10 – golden crownbeard VEEN Verbesina encelioides 0–10 – purslane PORTU Portulaca 0–5 – desert Indianwheat PLOV Plantago ovata 0–5 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 0–5 – sleepy silene SIAN2 Silene antirrhina 0–5 – crestrib morning-glory IPCO2 Ipomoea costellata 0–5 – Thurber's morning-glory IPTH Ipomoea thurberi 0–5 – spurge EUPHO Euphorbia 0–5 – slender goldenweed MAGR10 Machaeranthera gracilis 0–5 – tanseyleaf tansyaster MATA2 Machaeranthera tanacetifolia 0–5 – New Mexico thistle CINE Cirsium neomexicanum 0–5 – fewflower beggarticks BILE Bidens leptocephala 0–5 – Coulter's spiderling BOCO2 Boerhavia coulteri 0–5 – crested anoda ANCR2 Anoda cristata 0–5 – New Mexico thistle CINE Cirsium neomexicanum 0–5 – Coulter's spiderling BOCO2 Boerhavia coulteri 0–5 – aridland goosefoot CHDE Chenopodium desiccatum 0–5 – sleepy silene SIAN2 Silene antirrhina 0–5 – purslane PORTU Portulaca 0–5 – seaside heliotrope HECUO Heliotropium curassavicum var. oculatum 0–5 – longleaf false goldeneye HELOL Heliomeris longifolia var. longifolia 0–5 – crestrib morning-glory IPCO2 Ipomoea costellata 0–5 – Thurber's morning-glory IPTH Ipomoea thurberi 0–5 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 0–5 – sacred thorn-apple DAWR2 Datura wrightii 0–2 – spurge EUPHO Euphorbia 0–2 – green carpetweed MOVE Mollugo verticillata 0–2 – manybristle chinchweed PEPA2 Pectis papposa 0–2 – woolly plantain PLPA2 Plantago patagonica 0–2 – desert unicorn-plant PRAL4 Proboscidea althaeifolia 0–2 – doubleclaw PRPA2 Proboscidea parviflora 0–2 – spreading fanpetals SIAB Sida abutifolia 0–2 – Wright's thistle CIWR Cirsium wrightii 0–2 – southwestern pricklypoppy ARPL3 Argemone pleiacantha 0–2 – southwestern pricklypoppy ARPL3 Argemone pleiacantha 0–2 – green carpetweed MOVE Mollugo verticillata 0–2 – curlytop gumweed GRNUA Grindelia nuda var. aphanactis 0–2 – Coulter's horseweed LACO13 Laennecia coulteri 0–2 – woolly plantain PLPA2 Plantago patagonica 0–2 – desert unicorn-plant PRAL4 Proboscidea althaeifolia 0–2 – doubleclaw PRPA2 Proboscidea parviflora 0–2 – spreading fanpetals SIAB Sida abutifolia 0–2 – vervain VERBE Verbena 0–2 – Wright's thistle CIWR Cirsium wrightii 0–1 – sacred thorn-apple DAWR2 Datura wrightii 0–1 – American wild carrot DAPU3 Daucus pusillus 0–1 – Shrub/Vine6 Miscellaneous shrubs 5–75 fourwing saltbush ATCA2 Atriplex canescens 1–25 – Mojave seablite SUMO Suaeda moquinii 0–25 – Griffiths' saltbush ATGR2 Atriplex griffithsii 0–15 – cattle saltbush ATPO Atriplex polycarpa 0–15 – iodinebush ALOC2 Allenrolfea occidentalis 0–15 – shadscale saltbush ATCO Atriplex confertifolia 0–5 – mule-fat BASA4 Baccharis salicifolia 0–5 – rubber rabbitbrush ERNAL Ericameria nauseosa ssp. consimilis var. leiosperma 0–5 – pale desert-thorn LYPA Lycium pallidum 0–5 – broom dalea PSSC6 Psorothamnus scoparius 0–5 – southern goldenbush ISPL Isocoma pluriflora 0–2 – fringed twinevine FUCYC Funastrum cynanchoides ssp. cynanchoides 0–2 – Drummond's clematis CLDR Clematis drummondii 0–2 – longleaf jointfir EPTR Ephedra trifurca 0–2 – lotebush ZIOB Ziziphus obtusifolia 0–2 – broom snakeweed GUSA2 Gutierrezia sarothrae 0–1 – burroweed ISTE2 Isocoma tenuisecta 0–1 – desertbroom BASA2 Baccharis sarothroides 0–1 – 7 Succulents 0–20 candy barrelcactus FEWI Ferocactus wislizeni 0–5 – cactus apple OPEN3 Opuntia engelmannii 0–5 – hedgehog cactus ECHIN3 Echinocereus 0–1 – Tree8 Trees 5–100 western honey mesquite PRGLT Prosopis glandulosa var. torreyana 5–100 – velvet mesquite PRVE Prosopis velutina 0–25 – western soapberry SASAD Sapindus saponaria var. drummondii 0–15 – catclaw acacia ACGR Acacia greggii 0–15 – Table 7. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 8. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 9. Community 3.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 10. Community 4.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
Alkalai sacaton usually does not green up until the first summer rains in July, so the green season is the summer rainy season. Grazing must be concentrated in the summer to effectively utilize the forage resource. Areas of the site should be fenced exclusively for best management of alkalai sacaton. Herbaceous forage on the site will be deficient in digestible protein in the fall-winter-spring period. Burning or mowing can be used to freshen old growth alkalai sacaton. Burning should only be used in years with good winter-spring rainfall and should be done in late February to early March. Spring re-growth should not be grazed until the first summer rains. Several species of atriplex occur on the site but in such small quantities that the site is not valuable as winter forage area.
Free water is available some of the year in playa areas, natural charcos, and discontinuous gullies. This factor, in combination with the mixture of wooded areas and open grassland, make the site home to a variety of wildlife, and important for a variety of migratory waterfowl including sandhill cranes.Hydrological functions
This site occurs as grassy alluvial fans flanking the Willcox playa and as grassy floodplains along streams. It acts to absorb water and catch sediment from large flood events.
Recreational uses
Hunting, hiking, horseback riding, bird watching, photography
Wood products
In areas where mesquite has increased to moderate canopy levels (15-30%) there can be considerable fuel-wood available.
Supporting information
Inventory data references
Range 417s include 3 in good condition and 4 in fair condition.
Type locality
Location 1: Cochise County, AZ Township/Range/Section T13S R25E S31 General legal description Willcox Playa Contributors
Dan Robinett
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) Wilma Renken, Dan Robinett, Larry Humphrey, Gwen Dominguez, Scott Stratton Contact for lead author Tucson MLRA Soil Survey Office Date 08/07/2013 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
-
Number and extent of rills:
None. However, this site can have a few rills (discontinuous, 30-50 feet long) when an associated feature such as an adjacent road drains water from the site. -
Presence of water flow patterns:
Water flow paths occupy 40-50% of the surface area. They are discontinuous, 20-50 feet in length and show signs of strengthening with recent drought. -
Number and height of erosional pedestals or terracettes:
Pedestals are common on alkalai sacaton and mound saltbush. They are between 1-2 inches in height. Terracettes are uncommon on the site. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground from the pace frequency transect (300 pts) done on site was 63%. Gravel cover was 0% and basal cover of live perennial grasses was 5%. Vegetation occurs in patches with bare areas up to 5-8’ diameter. Bare areas are generally connected. -
Number of gullies and erosion associated with gullies:
None -
Extent of wind scoured, blowouts and/or depositional areas:
None -
Amount of litter movement (describe size and distance expected to travel):
Fine litter size classes are moving a few feet in bare areas and water flow areas. Coarse litter staying in place under grass and shrubs. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Values from a soil slake test average 3.3. About 50% of the ratings were 1-3s and 50% of the ratings were 4-6s. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
An1 horizon is a sandy clayloam, 1 inch thick with weak medium and thin platy structure and low organic matter. The An2 horizon (bisquit caps on columnar structure) is sandyloam with vesicular structure. Colors are 7.5 YR 7/2 dry and 7.5 YR 4/4 moist. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
A shrub, mound saltbush, and perennial grasses dominate the site. Alkalai sacaton grass canopy is 16.7% and mound saltbush canopy is 14% on this site. Annual forbs/grass canopy fluctuates with rainfall. Vegetation presents in a patchy distribution. Bare areas act as a watershed supplementing soil moisture of perennial vegetation patches. -
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
None present, average depth of penetration from an ARS field penetrometer with a 2.2 kg. sliding hammer, set at 20 inches fall height, is 6.4 cm. The dense (massive structure) siltyclay Btknz1 horizon at 3 inches can feel like a compacted layer. -
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 = shrubs >Sub-dominant:
annual grasses > annual forbs > perennial forbs > trees > succulentsOther:
Additional:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Mortality estimated at about 20% on perennial grasses, likely due to drought and grazing. Mortality on shrubs is estimated at 10%, also likely due to drought and grazing. -
Average percent litter cover (%) and depth ( in):
Litter cover ranged from 13-32%. Litter was generally confined to vegetation patches. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
422 lbs/ac. in a below average year; 1060 lbs/ac. in an average year; 2070 lbs/ac. in an above average year. Production of summer annual grasses can exceed expected on years with above average seasonal 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:
mesquite, tumbleweed and cocklebur -
Perennial plant reproductive capability:
Not impaired.
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