Natural Resources
Conservation Service
Ecological site R041XA120AZ
Shallow Hills
20-23" p.z.
(QUEM, QUAR, JUDE2)
Last updated: 4/09/2021
Accessed: 09/17/2026
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Draft. A draft ecological site description is either incomplete or has not undergone quality control and quality assurance review.
MLRA notes
Major Land Resource Area (MLRA): 041X–Madrean Archipelago
AZ 41.1 – Mexican Oak-Pine Forest and Oak Savannah
Elevations range from 4500 to 10,700 feet and precipitation ranges from 16 to 30 inches. Vegetation includes Emory oak, Mexican blue oak, Arizona white oak, one-seed juniper, alligator juniper, sacahuista, California bricklebush, skunkbush sumac, Arizona rosewood, wait-a-bit mimosa, sideoats grama, blue grama, purple grama, wooly bunchgrass, plains lovegrass, squirreltail, and pinyon ricegrass. The soil temperature regime ranges from thermic to mesic and the soil moisture regime ranges from aridic ustic to typic ustic. 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) Quercus emoryi
(2) Quercus arizonicaShrub (1) Juniperus deppeana
Herbaceous (1) Muhlenbergia emersleyi
Physiographic features
This site occurs on hills and mountains. Slope aspect is site differentiating at elevations near land resource subarea boundaries.
Table 2. Representative physiographic features
Landforms (1) Hill
(2) Mountain
Flooding frequency None Ponding frequency None Elevation 5600 – 7000 ft Slope 25 – 60 % Aspect N, E, S Climatic features
Precipitation in this zone of the common resource area ranges from 16-20 inches per year with elevations from 4700-5500 feet. Approximately 40% of this moisture comes as gentle rain or snow during the winter-spring (Oct-Apr) season; originates in the north Pacific and Gulf of California and comes as frontal storms with long duration and low intensity. The remaining 60% falls in the summer season (May-Sep); originates in the Gulf of Mexico and are convective, usually brief, intense thunderstorms. Snow is common Dec-Mar, averaging 5-15 inches per year, but rarely lasts more than a week. May and June are the driest months. Humidity is low.
Temperatures are mild. Freezing temperatures are common at night from Oct-May, but daytime temperatures are almost always over 40 F. Below 0 F temperatures can occur Dec-Feb. Daytime summer highs rarely exceed 95 F.
Species like plains lovegrass, bottlebrush squirreltail, Arizona white oak and Emory oak begin growth in late March to April. Warm season grasses begin growth in July or August with receipt of the first summer rains.Table 3 Representative climatic features
Frost-free period (average) 200 days Freeze-free period (average) Precipitation total (average) 20 in BarLineFigure 1. Monthly precipitation range
BarLineFigure 2. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
These are shallow to moderately deep soils formed on acid to neutral igneous rocks and related metamorphic rocks like schist, gneiss, arkose adn quartzite. They can also occur on non-calcareous sedimentary rocks like sandstone and conglomerate. These soils are dark colored in the surface and bedrock is slightly weathered into grus material (5-10 inches) at the soil juncture. Surfaces are well protected by covers of cobbles, rocks and gravels. Plant-soil moisture relationships are good. Numerous areas of rock outcrop occur intermingled with soil areas.
Soils mapped on this unit include: SSA-667 Santa Cruz area MU's FrE FrF & FtF Faraway, HoF Telephone Steep; SSA-669 Pima county Eastern part MU 28 Far & Spudrock; SSA-671 Cochise county Douglas-Tombstone part MU's 62 & 63 Far; SSA-703 Tohono O'odham Nation MU 22 Far & Spudrock.Table 4. Representative soil features
Surface texture (1) Very gravelly sandy loam
(2) Stony fine sandy loam
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Moderate to moderately rapid Soil depth 10 – 20 in Surface fragment cover <=3" 5 – 10 % Surface fragment cover >3" 10 – 20 % Available water capacity
(0-40in)0 – 2.5 in Soil reaction (1:1 water)
(0-40in)0 – 6 Subsurface fragment volume <=3"
(Depth not specified)15 – 20 % Subsurface fragment volume >3"
(Depth not specified)20 – 30 % 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 historic native state includes the native plant communities that occur on the site, including the historic climax plant community. This state includes other plant communities that naturally occupy the site following fire, drought, flooding, herbivores, and other natural disturbances. The historic climax plant community represents the natural climax community that eventually reoccupies the site with proper management.
Forest understory. Understory vegetation in areas that have experienced wildfire with the last ten years is dominated by perennial grasses. Forbs are most common sites that have recently burned. On areas that have not burned in a long time (20-30 years), the understory vegetation is dominated by shrubs.<br /> <br /> The potential plant community on this site is dominated by evergreen liveoak species, jniper and pinyon., Canopy cover ranges from 20-50%. An understory of perennial and annual forbs and grasses greatly diminishes as canopy cover increases. Large evergreen shrubs form a sub-canopy on the site. The aspect is evergreen woodland.<br /> <br /> Naturally occuring wildfires in June-Aug are an important factor in shaping these plant communities. Natural fire-free periods were probably quite long (20-30 years) because woody fuels take a long time to recover to preburn levels. Liveoak species nad large shrubs like sacahuista and silktassel resprout from root crowns after burning. Seeds of some species, especially manzanita, are scarified by fire, increasing the number of young plants greatly after a fire. Soil erosion on steep slopes can be severe after large-scale burns because understory vegetation is lacking at higher canopy covers. This acts to lengthen the fire-free intervals as new soil is slowly weathered from parent materials and trees and shrubs recover. Tree stems per acre range from 200-600. Lifespans for liveoaks range from 200-300 years. Above-ground annual growth of trees averages about 1% of net live volume in mature stands.<br /> <br /> Periodic severe drought can occur in this region. Severe drought, identified in tree ring chronologies, in southern Arizona i the 1670s and again in the 1950s, resulted in widespread tree mortality either due to drought alone or in combination with large scale forest fires which followed. A less severe drought in 1988-89 resulted in localized mortality of manzanita and a distinct late spring deciduous period for Emory and Arizona white oak on this site. Another drought in 1993-94 resulted in large-scale wildfires in some areas of these woodlands.
Table 5. Soil surface cover
Tree basal cover 0% Shrub/vine/liana basal cover 0-0% Grass/grasslike basal cover 10-20% Forb basal cover 0-0% Non-vascular plants 0-0% Biological crusts 0-10% Litter 30-60% Surface fragments >0.25" and <=3" 0-20% Surface fragments >3" 0-10% Bedrock 0% Water 0% Bare ground 10-20% Table 6. Canopy structure (% cover)
Height Above Ground (ft) Tree Shrub/Vine Grass/
GrasslikeForb <0.5 – 0-1% 0-5% 0-5% >0.5 <= 1 – 0-1% 5-15% 1-10% >1 <= 2 – 0-1% 30-45% 0-2% >2 <= 4.5 – 0-1% 0-10% 0-1% >4.5 <= 13 0-1% – – – >13 <= 40 – – – – >40 <= 80 – – – – >80 <= 120 – – – – >120 – – – – Additional community tables
Table 7. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
This site is not suited to summertime grazing by cattle. It is suitable to grazing by cattle in the winter-spring period when cool weather and free water permit more even use of the rugged terrain. It is suited to other species of livestock at any season (horses, goats), however, yearlong grazing should not be practiced on this site. Mountain lion predation on calves is severe on this site. Cows should be removed from areas of this site when they calve in the spring to avoid mountain lion predation.
A very productive and widely used habitat by wildlife. This moderately open woodland supports high densities of Coues whitetail deer. Water developments are very important to whitetail deer on this site. Natural water occurs infrequently as springs or seeps except in areas adjacent to perennial springs. Acorn production can be very high on this site, with mature trees of Emory or Arizona white oak producing up to 10,000 nuts per tree. Mountain lion use this site extensively, has all its habitat elements met and occusa in high densities in southern Arizona on this site. Black bear use the site as foraging habitat, especially when acorns and manzanita berries are available.Wood products
Net annual growth of oaks on this site averages about 1% of total volumn. Heart-rot sets in on stems at 20+ years of age. If harvested on a 25-30 year rotation, production of coppice volume will be much higher (3% of total volume) than yearly production of old age stands (due to lack of heartrot). CMAI for coppice rotation on this site ranges from 5-15 ft3/ac/yr. These species take a long time to reach sexual maturity. Emory oak does not bear acorns until 40 yrs old. Arizona white oak does not bear acorns until 80 yrs old. Productivity declines rapidly after 160 yrs of age. Livespan of these species are from 200-300 years. Dead limbs in mature stands range from 10-15% of total volume. Trees with 12-inch diameter stems are probably between 60-80 yrs old. Emory oak grows rapidly from 0-10 yrs, moderately from 10-20 yrs and slowly from 20 yrs on.
Equipment is limited by severe slopes (25%+), and unsurfaced roads on steep grades. Soils are moderately stony. Flooding probability is slight. Cleared areas/bare ground are subject to severe erosion due to shallow soils, high rainfall factors and steep slopes. The same is true for roads and trails.
Compaction potential is slight to moderate since soils are shallow and coarse textured. Workability for roads is moderate to severe due to shallow soils and hard bedrock. Rutting potential is severe due to steep slopes and shallow soils. Revegetation potential is good due to excellent climate.
Harvest cutting should be limited to areas with slopes less than 15%. A 25-30 year rotation on coppice sprouts will result in maximum wood products. Prescriptions should be designed to preserve other values like wildlife, scenic, forage, and hydrologic.
Prescribed buring in the cool season can reduce woody fuels and open tree canopies. Fire breaks need to be designed to keep grades below 20% and have water control features at regular intervals as needed to reduce roadway erosion.
Coppice harvest at 25-30 year intervals will avoid loss of productivity from heart rot fungus.
Natural regeneration is very good. Oak species and alligator juniper sprout readily after fire or cutting. Plant competition is slight. Thin understory vegetation offers little competition to either sprouts or seedlings of major tree species.Other products
Beargrass fiber is used for basket and broom makeing. Bellotas (acorns) from Emory oak are used for human consumption, as are pinyon nuts from the Mexican Pinyon. Young pinyon trees are used for Christmas trees. Manzanita, rosewood, and mahogany are used as novelty woods.
Supporting information
Type locality
Location 1: Cochise County, AZ Township/Range/Section T21S R19E S33 General legal description Ft. Huachuca - Coyote Canyon Location 2: Pinal County, AZ Township/Range/Section T14S R16E S36 General legal description Saguaro National Monument - Rincon Mountains Location 3: Cochise County, AZ Township/Range/Section T23S R23E S11 General legal description Douglas FO - Escabrosa Ridge, Mule Mountains Location 4: Graham County, AZ Township/Range/Section T9S R24E S19 General legal description Safford FO - Fort Grant, Graham Mountains Contributors
Karlynn Huling
Larry D. EllicottApproval
Curtis Talbot, 4/09/2021
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 09/17/2026 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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