Natural Resources
Conservation Service
Ecological site F041XA129AZ
Mountains
25-30" p.z.
(PSME, PIPO)
Last updated: 4/09/2021
Accessed: 08/25/2026
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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) Pseudotsuga menziesii
(2) Pinus ponderosaShrub Not specified
Herbaceous (1) Muhlenbergia
Physiographic features
This site occurs on hillslopes, toeslopes and ridgetops. Slope aspect is site differentiating at elevations near land resource area boundaries.
Table 2. Representative physiographic features
Landforms (1) Mountain slope
(2) Hill
(3) Ridge
Flooding frequency None Ponding frequency None Elevation 8000 – 9300 ft Slope 5 – 75 % 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 a variety of parent materials. They ae non-calcareous and have a thick (3-8 inches) dark-colored surface layer of rotting pine and fir needles (duff) over a light-colored eluvial (leached) horizon. Subsoils range in texture from very gravelly loams to gravelly clay loams. Bedrock ranges from hard to slightly weathered (5-10 inches) at the soil juncture. Soil reaction is acidic. Surfaces are fairly well protected with covers of boulders, rocks, cobbles 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-669 Pima county Eastern part MU 77 Lemon & Spudrock.Table 4. Representative soil features
Parent material (1) Alluvium – granite
(2) Colluvium – schist
Surface texture (1) Very flaggy sandy loam
(2) Flaggy loam
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Slow to moderately rapid Soil depth 20 – 40 in Surface fragment cover <=3" 5 – 10 % Surface fragment cover >3" 10 – 25 % Available water capacity
(0-40in)0 – 5 in Calcium carbonate equivalent
(0-40in)10 – 20 % Subsurface fragment volume <=3"
(Depth not specified)15 – 35 % 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 potential plant community on this site is a mixed stand of pine species and Douglas fir. Shrubs, perennial grasses and forbs are common in the understory. Canopy cover in mature stands range from 50-70%. Mature tree heights average 70 feet. The aspect is coniferous woodland.
The lower limit of these woodlands is controlled by drought and soil moisture regimes. These woodlands occur above the Arizona and ponderosa pine belts and on steep, northern aspects at lower elevations. Pines are successional to Douglas fir on this site.
Naturally occuring wildfires in the May-Aug lightening season are an important factor in shaping these woodlands. Natural fire-free intervals averages 9-10 years in drier areas up to 20 years in wetter areas. The natureal fire regime consisted of low intensity surface fires. These tended to favor Ponderosa and Arizona pines over Douglas fir. Young fir trees growing in the shade of pine ccanopies are more easily killed by surface fires because the bark is thinner and the foilage closer to the ground. The lack of fire in the last century on may areas of the site has led to a dominance of Douglas fir and unnaturally thick stands of trees. Fire prepares a mineral soil seedbed needed by both pine and fir species. In wetter soil areas on steep north exposures, quaking aspen is successional to Douglas fir. Aspens are easily top killed by fire, but the clones live 100s of years. In the infrequent stand where fires have killed fir and pine trees, these moist areas become dense stands of aspen sprouts. Densities as high as 2000 stems per acre are common. Aspen matures between 60-80 years of age and declines rapidly after 120 years. As these stands of aspen mature, Douglas fir saplings establish in the shade and grow to assume dominance in the next 40-50 years. On drier areas where aspen is not present, after stand replacing fires, shrub like (Fendler buckbrush, New Mexico thimbleberry, mountain snowberry, manzanita, netleaf, Plamers and silverleaf oak, and New Mexico locust) can form into dense growth. The shrubby aspect yields in time to pine and finally to Douglas fir.
Dwarf mistletoe (Arceuthobium vaginatum var. cryptopodum) infects Arizona and ponderosa pines. Another species (Arceuthobium Douglasii) infects Douglas fir. These mistletoes act to increase mortality, reduce growth and production, reduce seed yields and can predispose trees to attach by pine beetles. Mistletoe causes witches broom in branches, which increases crown flammability during wildfire. Snow breaks off branches with brooms, increasing fuel loading on the forest floor.
Pine beetles of the genus Dendroctonus attach both Douglas fir and pines. Infestations can kill healthy trees.
The spruce budworm (Choristonewra Douglas99) attacks immature stands of Douglas fir reducing growth, foilage volume, cone production and predisposes trees to attach by pine beetles. Outbreaks occur on average every 30-40 years. Uneven age, multi-story stands are more susceptable because more sunlight can penetrate to the forest floor, thus creating warmer, drier conditions conducive to budworms.
Exclusion of wildfires favor multi-story stands of shade tolerant species like Douglas fir, which spruce budworm prefers. Fire exclusion allows stands to thicken, making it easier for mistletoe to spread and suppressed growth weakens trees increasing attack by pine beetles. Allowing fires to burn naturally in open stands takes out damaged trees and favors one or two storied forests less conducive to spruce budworm outbreaks.
Tree stocking in these woodlands range from 50-200 trees per acre. Site index ranges from 60-70 for pines and 50-60 for Douglas fir. 100-yr old Douglas fir trees average 60 feet in height and 20 inches in diameter. Canopy cover in mature stands averages 60%.
Periodic severe drought can occur in this region. Stand replacing fires usually follow periods of severe drought. A drought in the 1950s caused large wildfires in these woodlands. A less severe drought in 1993-94 caused large wildfires in areas of this site as well.
Forest understory. Understory production varies not only with percent canopy cover, but also with the time from the last fire in the area. The figures shown are for woodlands 8-10 years after a fire. Understory production peaks 3-4 years after a fire.
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)Tree 5000 – 6500 Total 5000 – 6500 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Tree1 Dominant Tree 5000–6500 ponderosa pine PIPOS Pinus ponderosa var. scopulorum 2000–5000 – Douglas-fir PSME Pseudotsuga menziesii 1500–4000 – Interpretations
Animal community
This site produces very little forage for livestock. Very steep slopes and deep witner snow will preclude any significant use of this site except in summer. Mountain lion predation can be severe on calves in the spring and summer on this site.
This site is home to a variety of wildlife species. Two species of turkey and two species of tree squirrels exist in this habitat. The site is important to Coues whitetail deer. Black bear use the site extensively and need large unfragmented areas in association iwth pine and spruce-fir at higher elevations to survive. The site is home to one candidate species, the Northern goshawk, as well as two threatened species, the Mexican spotted owl and the American peregrine falcon. The Mexican spotted owl nests in clumps of Douglas fir and pine. Free water occurs infrequentlly on the site as springs, seeps or streamflow. Snags are very important for a variety of birds and small mammals and their predators. Small water catchments (overtank aprons) usually provide year-round water at these elevations if there is average precipitation.
Understory production varies not only with percent canopy cover, but also with the time from the last fire in the area. The figures shown are for woodlands 8-10 yrs after a fire. Understory production peaks 3-4 yrs after fire.
Average year production:
30% sparse: 500
50% medium: 250
70% dense: 100Wood products
These woodlands are in Site Productivity Class 4R. Arizona and ponderosa pine can live 300-500 years. Douglas fir can live 500-1000 years. Number of trees per acre in mature stands ranges from 50-200. Basal area of maturity ranges from 150-300 square feet per acre. Board feet volume of mature stands range from 15-20 thousand. Average age to reach diameter breast height is 12-13 years. Ponderosa and Arizona pines have the ability to release at any age. Proper spacing for maximum production of pines on this site is D=12 (diameter +12) in feet. Pines produce good seed crops every 3-5 years. Pine seeds are heavy and do not disperse over a wide area.
Douglas fir seedlings need shade for establishment. They will grow under a pine canopy and those individuals surviving the natural fire regime will eventually become co-dominants. Fir produces good seed crops every 5-7 years. Douglas fir seeds are light and can disperse over a wide area. Down and dead fuel loads in mature stands with natural fire regime average 1-3 tons per acre. In stands protected from fire for a long time, down and dead fuels can be as high as 30 tons per acre.
Equipment limits are severe due to very steep slopes. Unsurfaced roads are subject to washouts due to steep slopes and shallow soils. The area is has very stony, cobbly soils and rock outcrops and talus which also limits equipment use. Flooding hazard is slight.
Erosion potential is severe in cleared areas and roads and trails due to shallow, erodible soils, very steep slopes and high R factors.
Compaction potential of soils is slight to moderate. Workability is difficult for roads due to shallow soils and hard bedrock. Rutting potential is severe. Revegetation potential is good due to excellent climate.
This site is not well suited to harvest cutting due to very steep slopes. Thinning can be done to reduce fire hazard and release trees in doghair thickets.
Prescribed burning in Oct-Nov to remove debris from thinning operations is recommended. Burning will reduce pine beetles living in debris and will reduce fire hazards in the May-Aug fire season. Prescribed burning in the late spring can be used to thin unnaturally thick stands, but needs to be followed with fall burns to consume down and standing dead remaining from the initial burn. Once stands have been thinned and burned, naturally occuring wildfires should be allowed to burn.
For pest control, use pruning, thinning and prescribed burning to control pine beetles, spruce budworm and dwarf mistletoe.
Pine species and Douglas fir need fire to prepare a mineral soil seedbed for natural regeneration to occur.
To replant, pine cones should be collected Sep-Oct. 250 closed cones equal one bushel. 100 lbs. fresh cones yield 2-7 lbs. of seed. There are 12,000 seeds per lb. Douglas fir cones should be collected Aug-Sep. There are 1,000 cones per bushel; 42,000 seeds per lb. Stratify both fir and pine seeds at 41 F for 30-60 days then plant in containers in the spring. Plant seedlings in the field in the summer. Plant competition is slight for seedlings after a fire.
Windthrow hazard is slight as most areas of this site are on steep north aspects on the lee side of prevailing winds.
Douglas fir AZ & Ponderosa pine Gambel Oak SW White pine
Site index 50-60 60-70 --- 60-70
CMAI *(ft3/az/yr) 15-30 15-40 0-1/2 5-15
Fuelwood(cords/ac)(oak spec) --- --- ½-1 ---
Christmas trees/ac (Douglas fir) 5-30 --- --- ---
Productivity class (m3ha) 1-2 1-2 --- 0-1/2
Other products
Pine cones and wildflowers for decorative uses.
Mushrooms and fungi for food and mind-bending experiences.
Berries and fruits for jams and jellies.Other information
Threatened or endangered plants and animals:
New Mexican Ridgenose rattlesnake (Crotalus willardi obscurus)
Thick-billed parrot (Rhynchopsitta pachyrhycha)
American peregrine falcon)Falco peregrinus anatum)
Mexican spotted owl (Strix occidentalis lucida)
Mexican grey wolf (Canis lupus baileyi)
Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis)
Ocelot (Felis pardalis)Supporting information
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 08/25/2026 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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