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Ecological site R035XB238AZ

Sandy Terrace 6-10" p.z. Sodic

Accessed: 12/22/2024

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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.

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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): 035X–Colorado Plateau

This ecological site occurs in Common Resource Area 35.2 - the Colorado Plateau Shrub – Grasslands

Elevations range from 3800-5800 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) Sarcobatus vermiculatus
Herbaceous	(1) Sporobolus airoides (2) Pleuraphis jamesii

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Physiographic features

This site occurs adjacent to seeps and on high stream terraces that may still flood during high flows, but primarily benefit from lateral unground water movement from the stream bed. The soils are very deep and well drained sodic soils.

Table 2. Representative physiographic features

Landforms	(1) Stream terrace (2) Plateau
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	None to rare
Elevation	3,800 – 5,800 ft
Slope	10%
Aspect	Aspect is not a significant factor

Climatic features

The 35.2 Colorado Plateau Cold Desert Shrub - Grassland common resource area has a very dry and windy climate that is hot in the summer and cold in the winter. The annual precipitation averages between 6 and 10 inches. The soil moisture regime is typic aridic and the soil temperature regime is mesic. A slight majority of the precipitation arrives during the late fall, winter, and early spring. This winter season moisture originates in the Pacific Ocean and arrives as rain, or sometimes snow, during widespread frontal storms of generally low intensity. The majority of the snow (average range of 1 to 17 inches) falls from December through February, but rarely lasts more than a few days. A seasonal drought occurs from late May through early July. Summer rains occur from July through September during brief intense local thunderstorms. The rain is sporadic in intensity and location. The moisture originates from the Gulf of Mexico in the early summer and the Gulf of California in the late summer/early fall. Windy conditions are common year round, but the winds are strongest and most frequent during the spring.

Table 3. Representative climatic features

Frost-free period (average)	181 days
Freeze-free period (average)	207 days
Precipitation total (average)	10 in

Bar

Line

Figure 2. Monthly precipitation range

Bar

Line

Figure 3. Monthly average minimum and maximum temperature

Influencing water features

The soil moisture on this ecological site comes from precipitation and supplemental moisture from seeps or storm events. The terrace sites may flood occasionally, but primarily benefit from lateral underground water movement from the streambed that can last for weeks after storm events. This additional moisture allows this site to produce more vegetation than upland sites that depend entirely on rainfall.

Soil features

Soils on this site are sodic, deep and well to excessively well drained. The surface textures include loamy sand to fine sandy loam. Subsurface textures include loamy fine sand, fine sand, silt loam, sandy clay loam, clay loam, fine sandy loam. They are formed in eolian and alluvium derived from sandstone, siltstone and shale. The moisture regime is Typic Aridic and the temperature regime is Mesic.

Typical taxonomic units include:

SSA 707 Little Colorado River Valley Area MU's 22 Tuba, 52 Sheppard, 52 Psammaquents, 62 Tyende;
SSA-713 Chinle Area MU's 24 Nazlini, 46 Aneth;
SSA 717 Shiprock NM - MU's 165 Jeddito, 512 Gotho, and 519 & 523 Shumbegay.

Table 4. Representative soil features

Parent material	(1) Eolian deposits – sandstone and siltstone (2) Alluvium – shale
Surface texture	(1) Loamy fine sand (2) Fine sandy loam
Family particle size	(1) Loamy
Drainage class	Well drained to excessively drained
Permeability class	Moderately slow to rapid
Soil depth	60 in
Surface fragment cover <=3"	Not specified
Available water capacity (0-40in)	5 – 10 in
Electrical conductivity (0-40in)	8 mmhos/cm
Sodium adsorption ratio (0-40in)	13 – 30
Soil reaction (1:1 water) (0-40in)	7.9 – 9
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.

The State and Transition model shows the most common occurring plant communities likely to be encountered on this ecological site. This model may not show every possible plant community, but only those that are most prevalent and observed through field inventory. As more data is collected these plant communities may be revised, removed, and some added to reflect the ecological dynamics of this site.

State and transition model

Custom diagram

Standard diagram

Figure 4. STM - R035XB238AZ

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 text

State 1
Reference State

The reference state is dominated by a mix of greasewood, alkali sacaton and galleta. The canopy is dominated by greasewood.

Community 1.1
Native Shrubland/ Grassland (HCPC)

Figure 5. Sandy Terrace 6-10" p.z. Sodic

This site has a plant community made up of mid and short grasses with a relatively small percentage of forbs and a dominant aspect of shrubs. In the original plant community there is a predominance of shrubs and half shrubs with a mix of warm and cool season grasses. Plant species most likely to invade or increase on this site when it deteriorates are black greasewood, Torrey seepweed, shadscale, mound saltbush and annuals. Continuous grazing during the winter and spring periods will decrease the cool season grasses, which are replaced by lower forage value grasses and shrubs.

Figure 6. 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)
Shrub/Vine	180	275	385
Grass/Grasslike	130	200	280
Forb	5	15	25
Total	315	490	690

Table 6. Ground cover

Tree foliar cover	0%
Shrub/vine/liana foliar cover	10-20%
Grass/grasslike foliar cover	0-3%
Forb foliar cover	0-1%
Non-vascular plants	0%
Biological crusts	0%
Litter	0%
Surface fragments >0.25" and <=3"	0%
Surface fragments >3"	0%
Bedrock	0%
Water	0%
Bare ground	0%

Table 7. Canopy structure (% cover)

Height Above Ground (ft)	Tree	Shrub/Vine	Grass/ Grasslike	Forb
<0.5	–	–	–	0-1%
>0.5 <= 1	–	0-2%	0-2%	–
>1 <= 2	–	1-5%	0-2%	–
>2 <= 4.5	–	5-10%	–	–
>4.5 <= 13	–	0-1%	–	–
>13 <= 40	–	–	–	–
>40 <= 80	–	–	–	–
>80 <= 120	–	–	–	–
>120	–	–	–	–

Figure 7. Plant community growth curve (percent production by month). AZ3507, 35.3 10-14" p.z. alkali sacaton. Growth begins in late spring, most growth occurs in summer and early 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	0	5	20	15	20	30	10	0	0	0

Figure 8. 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 9. Plant community growth curve (percent production by month). AZ5201, 35.2 6-10" p.z. galleta. Growth begins in spring, most growth occurs during 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	20	10	15	35	5	0	0	0

Figure 10. 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 11. Plant community growth curve (percent production by month). AZ5205, 35.2 6-10" p.z. black greasewood. Growth occurs mostly in the spring and 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	20	25	10	10	15	10	5	0	0

State 2
Native/ Invaded State

Community 2.1
Greasewood Dominated

This site is dominated by greasewood with other low shrubs, such as shadscale, rabbitbrush, mound saltbush or Torrey seepweed. Grasses and forbs are present in small amounts. Bare ground is high and connected. Soil surface loss/erosion is the result of the loss of perennial herbaceous cover and sheet and rill erosion.

Transition T1A
State 1 to 2

Continuous Yearlong Grazing/ Drought/ Loss of surface horizon/Loss of perennial plant cover

Restoration pathway R2A
State 2 to 1

May not be possible due to significant loss of surface horizon. Mechanical Land Treatment/ Brush management/Reseeding/Prescribed Grazing System with Rest

Additional community tables

Table 8. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production (lb/acre)	Foliar cover (%)
Grass/Grasslike
1	Grasses			130–280
	alkali sacaton	SPAI	Sporobolus airoides	50–100	–
	James' galleta	PLJA	Pleuraphis jamesii	25–75	–
	sand dropseed	SPCR	Sporobolus cryptandrus	25–50	–
	Indian ricegrass	ACHY	Achnatherum hymenoides	0–35	–
	squirreltail	ELELE	Elymus elymoides ssp. elymoides	0–25	–
	Grass, perennial	2GP	Grass, perennial	0–25	–
Forb
2	Forbs			5–25
	Forb, perennial	2FP	Forb, perennial	5–15	–
	Forb, annual	2FA	Forb, annual	0–10	–
Shrub/Vine
3	Shrubs			180–385
	greasewood	SAVE4	Sarcobatus vermiculatus	200–250	–
	Mojave seablite	SUMO	Suaeda moquinii	5–25	–
	Shrub (>.5m)	2SHRUB	Shrub (>.5m)	5–25	–
	rubber rabbitbrush	ERNAB2	Ericameria nauseosa ssp. nauseosa var. bigelovii	0–20	–
	broom snakeweed	GUSA2	Gutierrezia sarothrae	0–20	–
	goldenbush	ISOCO	Isocoma	0–20	–
	mound saltbush	ATOB	Atriplex obovata	0–20	–
	shadscale saltbush	ATCO	Atriplex confertifolia	0–10	–
	Cutler's jointfir	EPCU	Ephedra cutleri	0–5	–

Interpretations

Animal community

This site is suitable for grazing during any period of the year by cows and calves, stocker cattle, sheep and horses. Prescribed grazing systems can benefit this site by allowing rest periods for the cool season species.

Wildlife diversity on this site is quite limited due to constancy of topography and vegetative form. This site does provide a significant forage substrate for adapted small species.

Recreational uses

Site is located on stable dunes and gently sloping terraces and plateaus which lend themselves to activities such as horseback riding, wildlife observation and hunting.

Winters are cold, however, relatively mild spring, fall and summer months are attractive to recreationists.

Supporting information

Type locality

Location 1: Apache County, AZ
Township/Range/Section	T39N R25E S3
General legal description	Mexican Water SW Quad; four miles east south east of Sand Springs; Section 3, T39N, R25E; Navajo Indian Reservation, AZ.

Other references

Updates and revisions for this ESD were conducted as part of a 2007-2012 Interagency Technical Assistance Agreement between the Bureau of Indian Affairs–Navajo Region and the NRCS-Arizona.

Contributors

Ken Gishi
Larry D. Ellicott
Steve Barker

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)	Kenneth Gishi
Contact for lead author	State Rangeland Management Specialist - NRCS State Office - Phoenix, AZ
Date	08/27/2012
Approved by
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
None expected on level slopes, very few on steeper slopes.
Presence of water flow patterns:
None on level slopes, very few on steeper slopes with widths of 1 to 2 feet when they do occur.
Number and height of erosional pedestals or terracettes:
None.
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground ranges from 40-65%.
Number of gullies and erosion associated with gullies:
None.
Extent of wind scoured, blowouts and/or depositional areas:
Few areas of wind scour occur in the interspaces. Some deposition may occur around shrubs and should be less than 6 inches in height.
Amount of litter movement (describe size and distance expected to travel):
Most fine litter will transported by wind or water, while woody litter tends to remain under canopies.
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
The expected average soil stability rating is 1-2.
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
The surface structure is typically moderate (thin, thick) platy structure with a thickness of 2 to 8 inches. Surface textures range from fine sand to fine sandy loam with colors typically light reddish brown to yellowish brown.
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
This site is characterized by an even distribution of shrubs and grasses. Herbaceous vegetation generally occurs throughout the shrub interspaces. Perennial grasses and other herbaceous vegetation promote infiltration and assist in slowing runoff moisture. This site when well vegetated is slightly to moderately effective at capturing moisture.
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
None. Some soils may a sodium-affected layer (Btn, Bn, or Cn) in the subsurface horizons. This layer is difficult to excavate and may be mistaken for a compacted layer. This layer may also be exposed in areas where the surface layer has been scoured or blown away.
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:
Salt Tolerant Shrubs (black greasewood, shadscale, Torrey seepweed) >>

Sub-dominant:
Warm season grasses > Cool season grasses >

Other:
Forbs > Other shrubs

Additional:
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
All plant functional groups are adapted to survival in all but the most severe droughts. Severe winter droughts affect shrubs the most. Severe summer droughts affect grasses the most.
Average percent litter cover (%) and depth ( in):
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Average annual production on this site is expected to be 450 to 550 lbs/ac. in a year of average annual 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:
Black greasewood, seepweed, mound saltbush and shadscale
Perennial plant reproductive capability:
All plants native to this site are adapted and are capable of producing seeds, stolons and rhizomes in all but the most severe drought.

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