Natural Resources
Conservation Service
Ecological site R035XB275AZ
Loamy Fan 6-10" p.z.
Accessed: 12/22/2024
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.
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): 035X–Colorado Plateau
AZ CRA 35.2 - Colorado Plateau Shrub – Grasslands
Elevations range from 3500-5500 feet and precipitation averages 6 to 10 inches per year. Vegetation includes shadscale, fourwing saltbush, Mormon tea, blackbrush, Indian ricegrass, galleta, blue grama, and black grama. The soil temperature regime is mesic and the soil moisture regime is typic aridic. This unit occurs within the Colorado Plateau Physiographic Province and is characterized by a sequence of flat to gently dipping sedimentary rocks eroded into plateaus, valleys and deep canyons. Sedimentary rock classes dominate the plateau with volcanic fields occurring for the most part near its margin.
Table 1. Dominant plant species
| Tree |
Not specified |
|---|---|
| Shrub |
(1) Atriplex elegans var. fasciculata |
| Herbaceous |
(1) Sporobolus airoides |
Physiographic features
This site occurs on alluvial fans and braided flood plains.
This site may receive some additional moisture from run-in off of adjacent areas, but most is lost to runoff.
This is an upland site.
Table 2. Representative physiographic features
| Landforms |
(1)
Alluvial fan
(2) Flood plain |
|---|---|
| Flooding duration | Extremely brief (0.1 to 4 hours) to very brief (4 to 48 hours) |
| Flooding frequency | None to rare |
| Ponding duration | Very brief (4 to 48 hours) to brief (2 to 7 days) |
| Ponding frequency | Rare to occasional |
| Elevation | 4,900 – 6,000 ft |
| Slope | 1 – 3% |
| Aspect | Aspect is not a significant factor |
Climatic features
The climate of the land resource unit is arid with warm summers and cool winters. This is one of the driest land resource units on the Colorado Plateau with an average annual precipitation ranging from 6 to 10 inches per year. It is also very erratic, often varying substantially from year to year. 40 to 50 percent of the precipitation is received from October through early May. This precipitation comes as gentle rain or snow from frontal storms coming out of the Pacific Ocean. Snow is common from November through February. Generally no more than an inch or two of snow accumulates and usually melts within a day or two. The remaining precipitation, approximately 50 to 60 percent, is received from July through September as spotty, unreliable and sometimes violent thunderstorms. The moisture for this precipitation originates in the Gulf of Mexico (and the Pacific Ocean in the fall) and flows into the area on the north end of the Mexican monsoon. Late May through late June is generally a dry period. The mean annual temperature ranges from 53 to 56 degrees Fahrenheit (F). The frost-free period (air temperature > 32 degrees F) ranges from 135 to 160 days (@ 50 percent probability). Strong winds are common, especially in the spring.
Table 3. Representative climatic features
| Frost-free period (average) | 160 days |
|---|---|
| Freeze-free period (average) | 184 days |
| Precipitation total (average) | 10 in |
Figure 2. Monthly precipitation range
Figure 3. Monthly average minimum and maximum temperature
Influencing water features
Soil features
Soils on this site are deep (40-60") and well drained. They are formed in alluvium derived from shale, siltstone and sandstone.
Surface textures include very fine sandy loam and loam.
Subsurface textures include very fine sandy loam and loam.
The hazard of water erosion is moderate and hazard of wind erosion is severe.
Typical taxonomic unit:
SSA 717 Shiprock NM - MU 230 Ravola.
Table 4. Representative soil features
| Parent material |
(1)
Alluvium
–
shale and siltstone
|
|---|---|
| Surface texture |
(1) Very fine sandy loam (2) Loam |
| Family particle size |
(1) Loamy |
| Drainage class | Moderately well drained to well drained |
| Permeability class | Moderately slow to moderate |
| Soil depth | 40 – 60 in |
| Surface fragment cover <=3" | Not specified |
| Surface fragment cover >3" | Not specified |
| Available water capacity (0-40in) |
7 – 10 in |
| Calcium carbonate equivalent (0-40in) |
5 – 25% |
| Electrical conductivity (0-40in) |
4 – 8 mmhos/cm |
| Sodium adsorption ratio (0-40in) |
5 – 13 |
| Soil reaction (1:1 water) (0-40in) |
7.4 – 8.4 |
| Subsurface fragment volume <=3" (Depth not specified) |
Not specified |
| Subsurface fragment volume >3" (Depth not specified) |
Not specified |
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 grazing, fire, 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 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
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Ecosystem states
State 1 submodel, plant communities
State 1
Historic Climax Plant Community
Community 1.1
Historic Climax Plant Community
This site has a plant community made up primarily of grasses with some forbs and shrubs. In the original plant community there is a predominance of warm season and cool season grasses. Plant species most likely to invade or increase on this site when it deteriorates are annual wheatgrass, annual barley, Russian thistle, cheatgrass, globemallow and other annual weeds. Continuous grazing during the winter and spring periods will decrease the cool season grasses, which are replaced by warm season, lower forage value plants.
Figure 4. 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 | 300 | 325 | 350 |
| Shrub/Vine | 50 | 88 | 125 |
| Forb | 25 | 38 | 50 |
| Total | 375 | 451 | 525 |
Figure 5. Plant community growth curve (percent production by month). AZ3521, 35.2 6-10" p.z. all sites. Growth begins in the spring and continues through the summer. Most growth in this CRA occurs in the spring using stored winter moisture..
| 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 | 1 | 9 | 20 | 27 | 14 | 10 | 11 | 5 | 3 | 0 | 0 |
Figure 6. Plant community growth curve (percent production by month). AZ5202, Indian ricegrass, 35.2 6-10" p.z.. Growth begins in spring, most growth occurs in May, goes dormant during summer heat..
| 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 | 10 | 15 | 40 | 20 | 0 | 0 | 10 | 5 | 0 | 0 |
Figure 7. Plant community growth curve (percent production by month). AZ5203, 35.2 6-10" p.z. alkali sacaton. Growth begins in the spring, most growth occurs in the summer, goes dormant in the fall..
| 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 | 20 | 10 | 20 | 20 | 10 | 5 | 0 | 0 |
Figure 8. Plant community growth curve (percent production by month). AZ5204, 35.2 6-10" p.z. bottlebrush squirreltail. Most growth occurs in the spring, plants may remain green during the winter..
| 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 | 5 | 40 | 40 | 5 | 0 | 0 | 0 | 0 | 5 | 5 | 0 |
Figure 9. Plant community growth curve (percent production by month). AZ5210, 35.2 6-10" p.z. mound saltbush. Growth begins in spring and continues through the summer. Seed stalk extension occurs in late summer with seed set in the fall..
| 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 | 20 | 25 | 15 | 15 | 10 | 5 | 5 | 0 | 0 |
Additional community tables
Table 6. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (lb/acre) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Shrub/Vine
|
||||||
| 1 | 50–125 | |||||
| wheelscale saltbush | ATELF | Atriplex elegans var. fasciculata | 25–50 | – | ||
| mound saltbush | ATOB | Atriplex obovata | 25–50 | – | ||
| winterfat | KRLA2 | Krascheninnikovia lanata | 0–15 | – | ||
| shadscale saltbush | ATCO | Atriplex confertifolia | 0–15 | – | ||
| valley saltbush | ATCU | Atriplex cuneata | 0–15 | – | ||
| Shrub (>.5m) | 2SHRUB | Shrub (>.5m) | 0–15 | – | ||
| fourwing saltbush | ATCA2 | Atriplex canescens | 0–5 | – | ||
|
Grass/Grasslike
|
||||||
| 2 | 300–350 | |||||
| alkali sacaton | SPAI | Sporobolus airoides | 125–150 | – | ||
| James' galleta | PLJA | Pleuraphis jamesii | 75–100 | – | ||
| Indian ricegrass | ACHY | Achnatherum hymenoides | 25–50 | – | ||
| squirreltail | ELELE | Elymus elymoides ssp. elymoides | 25–50 | – | ||
| Grass, perennial | 2GP | Grass, perennial | 0–15 | – | ||
| sand dropseed | SPCR | Sporobolus cryptandrus | 0–15 | – | ||
|
Forb
|
||||||
| 3 | 25–50 | |||||
| Forb, perennial | 2FP | Forb, perennial | 5–20 | – | ||
| globemallow | SPHAE | Sphaeralcea | 5–15 | – | ||
| Forb, annual | 2FA | Forb, annual | 0–5 | – | ||
| yellow spiderflower | CLLU2 | Cleome lutea | 0–5 | – | ||
| pepperweed | LEPID | Lepidium | 0–5 | – | ||
Interpretations
Animal community
This site is suited for yearlong grazing by all classes of livestock and is easily traversed. It will respond quickly to a Prescribed Grazing system. This site is susceptible to erosion, particularly overgrazed areas, old roads and concentration areas. The site may be somewhat inaccessible to livestock during the occasional brief periods following the summer thunderstorms.
This site is a wintering area for big game. This site offers a fair diversity in the vegetative complex for wildlife. In higher condition classes the site is most suitable to grassland wildlife species. As retrogression occurs the woody species increase and wildlife species utilizing the site may change.
Recreational uses
The grassy flood plains give an interesting scene from the adjacent sites that is aesthetically pleasing.
Winters are cold, and spring time is usually windy. The summers are typically mild with occasional Southwest thunderstorms that may cause brief periods of flooding.
Hunting, horsebsck riding and wildlife observation are occasional activities.
Supporting information
Type locality
| Location 1: San Juan County, NM | |
|---|---|
| Township/Range/Section | T27N R18W S6 |
| General legal description | Yellow Hill quad - about 13 miles southwest of Shiprock, NM - Navajo Reservation NM. |
Contributors
Harmon Hodgkinson
Karlynn Huling
Larry D. Ellicott
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 | |
| Approved by | |
| 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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