Natural Resources
Conservation Service
Ecological site R040XB231AZ
Lithic Hills 7"-10" p.z.
Last updated: 10/17/2024
Accessed: 11/21/2024
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.
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) 40-2, Middle Sonoran Desert, is characterized by desert scrub vegetation. A moderate amount of desert pavement is present on fan remnants. Trees are common in washes, bottoms and hillslopes. 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.
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 2 - Middle Sonoran Desert Ecological Site Lithic Hills, 7"-10" 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 Desert
Ecological site concept
Lithic Hills, 7"-10" p.z., occur on steep terrain, with slopes greater than 15%. Soils are calcareous, loamy textured, and very shallow to shallow over hard, unweathered bedrock. Exposed bedrock often covers more than 20% of the surface area. This ecological site was renamed from Limestone Hills, 7"-10" p.z., as parent materials are not limited to limestone.
Associated sites
| R040XB216AZ |
Sandy Wash 7"-10" p.z. Sandy Wash ecological site benefits from run-off originating on Lithic Hills |
|---|---|
| R040XB208AZ |
Limy Upland, Deep 7"-10" p.z. Limy Upland Deep ecological site situated on uplands below Lithic Hills |
| R040XB210AZ |
Limy Upland 7"-10" p.z. Limy Upland ecological site situated on upland below Lithic Hills |
Similar sites
| R040XB210AZ |
Limy Upland 7"-10" p.z. |
|---|
Table 1. Dominant plant species
| Tree |
Not specified |
|---|---|
| Shrub |
(1) Encelia farinosa |
| Herbaceous |
Not specified |
Physiographic features
This site occurs on steep hill-slopes and ridge-tops. Rock outcrops can cover more than 20% of the area.
Table 2. Representative physiographic features
| Landforms |
(1)
Mountain
(2) Hill (3) Mountain slope |
|---|---|
| Flooding frequency | None |
| Ponding frequency | None |
| Elevation | 366 – 610 m |
| Slope | 15 – 75% |
| Aspect | Aspect is not a significant factor |
Climatic features
Annual precipitation ranges from 7 to 10 inches. Annual rainfall is bimodal, with distinct rainy seasons occurring from December to March (winter) and July to September (summer). Rainfall ratios range from 40:60 (winter:summer) in the southern part, and 60:40 in the central and northern parts. 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. Winter precipitation is the most dependable water source for vegetation, and snowfall is very rare. During summer months, atmospheric activity in the Gulf of Mexico produces convective thunderstorms when crossing over the mountains in the afternoon. These storms travel across the plains and valleys, producing precipitation of short duration, usually less than 30 minutes, but of moderate to heavy intensity. Between these two seasons, little to no effective precipitation can occur for several months at a time. May and June are the driest months, and overall humidity is very low.
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 38% at Florence (east) to 46% at Aguila (west).
Winter temperatures are very mild, with very few days having short periods of freezing temperatures. Summertime temperatures are hot to very hot, with many days in June and July exceeding 105°F. The number of frost-free days ranges from 280 in major river valleys with cold air drainage to between 320 and 350 in upland areas.
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) | 291 days |
|---|---|
| Freeze-free period (average) | 344 days |
| Precipitation total (average) | 330 mm |
Figure 1. Monthly precipitation range
Figure 2. Monthly average minimum and maximum temperature
Influencing water features
Soil features
These shallow and very shallow soils form over bedrock. Parent material varies from sedimentary to igneous sources. Soils are calcareous throughout, and are very gravelly to cobbly. Plant-soil moisture relationships are poor, though the large rock outcrops concentrate precipitation to areas with soil.
Table 4. Representative soil features
| Surface texture |
(1) Very gravelly sandy loam (2) Gravelly sandy loam (3) Gravelly loam |
|---|---|
| Family particle size |
(1) Loamy |
| Drainage class | Somewhat excessively drained |
| Permeability class | Rapid to moderately rapid |
| Soil depth | 13 – 51 cm |
| Surface fragment cover <=3" | 30 – 60% |
| Surface fragment cover >3" | 5 – 20% |
| Available water capacity (0-101.6cm) |
1.27 – 5.08 cm |
| Calcium carbonate equivalent (0-101.6cm) |
0 – 20% |
| Electrical conductivity (0-101.6cm) |
0 – 2 mmhos/cm |
| Sodium adsorption ratio (0-101.6cm) |
0 – 2 |
| Soil reaction (1:1 water) (0-101.6cm) |
7.9 – 8.4 |
| Subsurface fragment volume <=3" (Depth not specified) |
35 – 65% |
| Subsurface fragment volume >3" (Depth not specified) |
0 – 10% |
Ecological dynamics
The potential plant community is a diverse mixture of desert trees, shrubs, cacti, half-shrubs and shrub-like perennial forbs. Drought conditions frequently occur. The sparse plant community and exposed bedrock effectively eliminate the occurrence of fire. The shallow, course-textured soils dry very quickly, greatly limiting the occurrence of shallow-rooted perennials. Rainfall infiltrates cracks in the bedrock, and plants become deeply rooted within these cracks. Shrubland is the only ecological state for this site. Plant-soil moisture relationships are poor. The aspect is open shrubland.
State and transition model
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Ecosystem states
State 1 submodel, plant communities
State 1
Shrubland
Community 1.1
Shrub-Cactus
The potential plant community is a diverse mixture of desert trees, shrubs, cacti, and perennial grasses and forbs. The large amount of rock outcrop on this site tends to concentrate precipitation onto adjacent soil areas. Brittlebush predominates on north-facing slopes while teddybear cholla predominates on south-facing slopes. Plant populations of range from 110 to 150 individuals per acre for brittlebush, 200 to 250 for teddybear cholla, 50 to 100 for creosotebush, 35 to 50 for ocotillo, and 1 to 10 for saguaro. Cryptogam cover on bare ground ranges from low to moderate. Plant-soil moisture relationships are poor. The aspect is shrubland.
Figure 3. 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) |
|---|---|---|---|
| Shrub/Vine | 112 | 252 | 387 |
| Forb | 11 | 13 | 28 |
| Grass/Grasslike | – | 2 | 11 |
| Total | 123 | 267 | 426 |
Table 6. Soil surface cover
| Tree basal cover | 0-1% |
|---|---|
| Shrub/vine/liana basal cover | 1-3% |
| Grass/grasslike basal cover | 0-1% |
| Forb basal cover | 0-1% |
| Non-vascular plants | 0% |
| Biological crusts | 0-15% |
| Litter | 0-20% |
| Surface fragments >0.25" and <=3" | 30-60% |
| Surface fragments >3" | 5-25% |
| Bedrock | 20-60% |
| Water | 0% |
| Bare ground | 5-25% |
Table 7. Canopy structure (% cover)
| Height Above Ground (m) | Tree | Shrub/Vine | Grass/ Grasslike |
Forb |
|---|---|---|---|---|
| <0.15 | – | 0-2% | 0-10% | 1-10% |
| >0.15 <= 0.3 | – | 0-2% | 1-5% | 1-10% |
| >0.3 <= 0.6 | – | 1-5% | 0-1% | 0-2% |
| >0.6 <= 1.4 | 0-1% | 1-5% | 0-1% | 0-1% |
| >1.4 <= 4 | 5-10% | – | – | – |
| >4 <= 12 | 0-1% | – | – | – |
| >12 <= 24 | – | – | – | – |
| >24 <= 37 | – | – | – | – |
| >37 | – | – | – | – |
Additional community tables
Table 8. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (kg/hectare) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Grass/Grasslike
|
||||||
| 1 | Miscellaneous perennial grasses | 0–6 | ||||
| slim tridens | TRMU | Tridens muticus | 0–2 | – | ||
| Parish's threeawn | ARPUP5 | Aristida purpurea var. parishii | 0–2 | – | ||
| Wright's threeawn | ARPUW | Aristida purpurea var. wrightii | 0–2 | – | ||
| spidergrass | ARTE3 | Aristida ternipes | 0–2 | – | ||
| cane bluestem | BOBA3 | Bothriochloa barbinodis | 0–2 | – | ||
| Arizona cottontop | DICA8 | Digitaria californica | 0–2 | – | ||
| desert needlegrass | ACSP12 | Achnatherum speciosum | 0–2 | – | ||
| Havard's threeawn | ARHA3 | Aristida havardii | 0–2 | – | ||
| 2 | Annual grasses | 0–50 | ||||
| sixweeks threeawn | ARAD | Aristida adscensionis | 0–11 | – | ||
| Rothrock's grama | BORO2 | Bouteloua rothrockii | 0–11 | – | ||
| sixweeks fescue | VUOC | Vulpia octoflora | 0–11 | – | ||
| prairie threeawn | AROL | Aristida oligantha | 0–6 | – | ||
| delicate muhly | MUFR | Muhlenbergia fragilis | 0–3 | – | ||
| Arizona signalgrass | URAR | Urochloa arizonica | 0–2 | – | ||
| desert lovegrass | ERPEM | Eragrostis pectinacea var. miserrima | 0–2 | – | ||
| Arizona brome | BRAR4 | Bromus arizonicus | 0–1 | – | ||
| needle grama | BOAR | Bouteloua aristidoides | 0–1 | – | ||
| sixweeks grama | BOBA2 | Bouteloua barbata | 0–1 | – | ||
|
Forb
|
||||||
| 3 | Dominant perennial forbs | 11–56 | ||||
| California fagonbush | FALA | Fagonia laevis | 1–6 | – | ||
| slender poreleaf | POGR5 | Porophyllum gracile | 1–6 | – | ||
| desert trumpet | ERIN4 | Eriogonum inflatum | 1–6 | – | ||
| trailing windmills | ALIN | Allionia incarnata | 0–6 | – | ||
| desert globemallow | SPAM2 | Sphaeralcea ambigua | 1–6 | – | ||
| slender janusia | JAGR | Janusia gracilis | 0–6 | – | ||
| Coues' cassia | SECO10 | Senna covesii | 0–3 | – | ||
| brownplume wirelettuce | STPA4 | Stephanomeria pauciflora | 0–2 | – | ||
| plains blackfoot | MELE2 | Melampodium leucanthum | 0–1 | – | ||
| scarlet spiderling | BOCO | Boerhavia coccinea | 0–1 | – | ||
| Parry's beardtongue | PEPA24 | Penstemon parryi | 0–1 | – | ||
| rosemallow | HIBIS2 | Hibiscus | 0–1 | – | ||
| paleface | HIDE | Hibiscus denudatus | 0–1 | – | ||
| narrowleaf silverbush | ARLA12 | Argythamnia lanceolata | 0–1 | – | ||
| glandleaf milkwort | POMA7 | Polygala macradenia | 0–1 | – | ||
| desert marigold | BAMU | Baileya multiradiata | 0–1 | – | ||
| leatherweed | CRPOP | Croton pottsii var. pottsii | 0–1 | – | ||
| dense ayenia | AYMI | Ayenia microphylla | 0–1 | – | ||
| New Mexico silverbush | ARNE2 | Argythamnia neomexicana | 0–1 | – | ||
| weakleaf bur ragweed | AMCO3 | Ambrosia confertiflora | 0–1 | – | ||
| 4 | Annual forbs and minor perennials | 1–73 | ||||
| phacelia | PHACE | Phacelia | 0–17 | – | ||
| desert Indianwheat | PLOV | Plantago ovata | 0–11 | – | ||
| lyreleaf jewelflower | STCA5 | Streptanthus carinatus | 0–11 | – | ||
| western tansymustard | DEPI | Descurainia pinnata | 0–11 | – | ||
| cryptantha | CRYPT | Cryptantha | 0–11 | – | ||
| California poppy | ESCAM | Eschscholzia californica ssp. mexicana | 0–11 | – | ||
| Gordon's bladderpod | LEGO | Lesquerella gordonii | 0–11 | – | ||
| Coulter's lupine | LUSP2 | Lupinus sparsiflorus | 0–11 | – | ||
| exserted Indian paintbrush | CAEXE | Castilleja exserta ssp. exserta | 0–11 | – | ||
| shaggyfruit pepperweed | LELA | Lepidium lasiocarpum | 0–6 | – | ||
| hairy prairie clover | DAMO | Dalea mollis | 0–6 | – | ||
| Texas stork's bill | ERTE13 | Erodium texanum | 0–6 | – | ||
| chia | SACO6 | Salvia columbariae | 0–2 | – | ||
| wishbone-bush | MILAV | Mirabilis laevis var. villosa | 0–2 | – | ||
| Florida pellitory | PAFL3 | Parietaria floridana | 0–1 | – | ||
| whitestem blazingstar | MEAL6 | Mentzelia albicaulis | 0–1 | – | ||
| foothill deervetch | LOHU2 | Lotus humistratus | 0–1 | – | ||
| Mexican fireplant | EUHE4 | Euphorbia heterophylla | 0–1 | – | ||
| Parish's larkspur | DEPAP3 | Delphinium parishii ssp. parishii | 0–1 | – | ||
| flatcrown buckwheat | ERDE6 | Eriogonum deflexum | 0–1 | – | ||
| sleepy silene | SIAN2 | Silene antirrhina | 0–1 | – | ||
| slimjim bean | PHFI3 | Phaseolus filiformis | 0–1 | – | ||
| Arizona popcornflower | PLAR | Plagiobothrys arizonicus | 0–1 | – | ||
| woolly tidestromia | TILA2 | Tidestromia lanuginosa | 0–1 | – | ||
| pricklyleaf dogweed | THAC | Thymophylla acerosa | 0–1 | – | ||
| sand fringepod | THCU | Thysanocarpus curvipes | 0–1 | – | ||
| desert mariposa lily | CAKE | Calochortus kennedyi | 0–1 | – | ||
| whitemargin sandmat | CHAL11 | Chamaesyce albomarginata | 0–1 | – | ||
| brittle spineflower | CHBR | Chorizanthe brevicornu | 0–1 | – | ||
| hyssopleaf sandmat | CHHY3 | Chamaesyce hyssopifolia | 0–1 | – | ||
| Palmer's Indian mallow | ABPA | Abutilon palmeri | 0–1 | – | ||
| brownfoot | ACWR5 | Acourtia wrightii | 0–1 | – | ||
| San Felipe dogweed | ADPO | Adenophyllum porophylloides | 0–1 | – | ||
| tuber anemone | ANTU | Anemone tuberosa | 0–1 | – | ||
| rockcress | ARABI2 | Arabis | 0–1 | – | ||
| aster | ASTER | Aster | 0–1 | – | ||
| Coulter's spiderling | BOCO2 | Boerhavia coulteri | 0–1 | – | ||
| hoary bowlesia | BOIN3 | Bowlesia incana | 0–1 | – | ||
| Arizona wrightwort | CAAR7 | Carlowrightia arizonica | 0–1 | – | ||
|
Shrub/Vine
|
||||||
| 5 | Dominant low shrubs | 45–163 | ||||
| white ratany | KRGR | Krameria grayi | 6–28 | – | ||
| brittlebush | ENFA | Encelia farinosa | 17–28 | – | ||
| burrobush | AMDU2 | Ambrosia dumosa | 6–17 | – | ||
| whitestem paperflower | PSCO2 | Psilostrophe cooperi | 1–11 | – | ||
| littleleaf ratany | KRER | Krameria erecta | 1–11 | – | ||
| pelotazo | ABIN | Abutilon incanum | 0–11 | – | ||
| triangle bur ragweed | AMDE4 | Ambrosia deltoidea | 0–11 | – | ||
| woody crinklemat | TICAC | Tiquilia canescens var. canescens | 0–11 | – | ||
| desert zinnia | ZIAC | Zinnia acerosa | 0–6 | – | ||
| broom snakeweed | GUSA2 | Gutierrezia sarothrae | 0–2 | – | ||
| American threefold | TRCA8 | Trixis californica | 0–2 | – | ||
| 6 | Dominant large shrubs | 45–112 | ||||
| ocotillo | FOSP2 | Fouquieria splendens | 17–56 | – | ||
| creosote bush | LATR2 | Larrea tridentata | 11–28 | – | ||
| whitethorn acacia | ACCO2 | Acacia constricta | 0–11 | – | ||
| yellow paloverde | PAMI5 | Parkinsonia microphylla | 2–11 | – | ||
| 7 | Miscellaneous shrubs | 6–28 | ||||
| Nevada jointfir | EPNE | Ephedra nevadensis | 0–2 | – | ||
| Warnock's snakewood | COWA | Condalia warnockii | 0–2 | – | ||
| lotebush | ZIOB | Ziziphus obtusifolia | 0–1 | – | ||
| javelina bush | COER5 | Condalia ericoides | 0–1 | – | ||
| knifeleaf condalia | COSP3 | Condalia spathulata | 0–1 | – | ||
| desert lavender | HYEM | Hyptis emoryi | 0–1 | – | ||
| water jacket | LYAN | Lycium andersonii | 0–1 | – | ||
| Arizona desert-thorn | LYEX | Lycium exsertum | 0–1 | – | ||
| algerita | MATR3 | Mahonia trifoliolata | 0–1 | – | ||
| 8 | Cactus | 17–84 | ||||
Interpretations
Supporting information
Other references
Griffith, G.E., Omernik, J.M., Johnson, C.B., and Turner, D.S., 2014, Ecoregions of Arizona (poster): U.S. Geological Survey Open-File Report 2014-1141, with map, scale 1:1,325,000, https://dx.doi.org/10.3133/ofr20141141. ISSN 2331-1258 (online)
United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296.
Approval
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 | 11/21/2024 |
| Approved by | Kendra Moseley |
| Approval date | |
| Composition (Indicators 10 and 12) based on | Annual Production |
Indicators
-
Number and extent of rills:
-
Presence of water flow patterns:
-
Number and height of erosional pedestals or terracettes:
-
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
-
Number of gullies and erosion associated with gullies:
-
Extent of wind scoured, blowouts and/or depositional areas:
-
Amount of litter movement (describe size and distance expected to travel):
-
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
-
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
-
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
-
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
-
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:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
-
Average percent litter cover (%) and depth ( in):
-
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
-
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:
-
Perennial plant reproductive capability:
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