Natural Resources
Conservation Service
Ecological site R035XB016NM
Clay Loam Terrace (Sodic)
7-10"
Last updated: 5/20/2025
Accessed: 04/30/2026
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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.
Ecological site concept
This site occurs on low stream and fan terraces of valley floors and below mesas and cuestas. The soils are very deep and well drained, with textures that are quite variable*. The soils are moderately to very strongly alkaline (pH 7.9 - 9.6). They are very slightly to strongly saline (EC 2-16) and slightly to moderately sodic (SAR 5-30).
*The site name would suggest that soils have clay loam textures, and we imagine this is the case most of the time. However, the Soil Features section includes such textures as fine sandy loam.Table 1. Dominant plant species
Tree Not specified
Shrub (1) Atriplex obovata
Herbaceous (1) Sporobolus airoides
Physiographic features
This site occurs on low stream and fan terraces of valley floors and below mesas and cuestas. It may receive some additional run-in moisture from surrounding areas, but little benefit is realized because of the soil properties. Slopes range from 0 to 5 percent. Elevations range from 4,700 to 6,100 feet.
Table 2. Representative physiographic features
Landforms (1) Stream terrace
(2) Fan remnant
Flooding duration Very brief (4 to 48 hours) Flooding frequency None to rare Ponding frequency None Elevation 4700 – 6100 ft Slope 0 – 5 % Water table depth 60 – 0 in Aspect Aspect is not a significant factor Climatic features
Mean annual precipitation varies from 7 to 10 inches. About 60% of this moisture comes as rain from April through October. May and June are the driest months. Most of the moisture from November through March comes as snow. Winds of high velocity during late winter and early spring are common.
Mean temperatures for the hottest month, July, are about 83 degrees F. The coldest month is January, when the mean temperature is about 27 degrees F. Extreme temperatures of 104 degrees F and –17 degrees F have been recorded. Frost-free period ranges from 140 to 160 days.
The cool-season plants start growth in March and end with plant maturity and seed dissemination about mid-June. Warm-season plants grow from June through September, taking advantage of the moisture and warmth from tropical air out of the Gulf of Mexico. About 40% of the total precipitation is received during these summer months. The other 60%, received from fall through spring, influences cool-season plants.Table 3 Representative climatic features
Frost-free period (average) 160 days Freeze-free period (average) 170 days Precipitation total (average) 10 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
This is an upland site, and is not associated with water features or wetlands. During heavy rain events, this site may receive run-on moisture from landforms above and contribute runoff to landforms below.
Soil features
The soils are very deep and well drained. They formed in alluvium derived from shale, siltstone, and sandstone. Surface textures include clay loam, sandy clay loam, silty clay loam, loam, and very fine sandy loam. The subsoil has textures of silty clay loam, silty clay, sandy clay loam, loam, clay loam, and fine sandy loam. Permeability is moderately to very slow. Available water capacity is low to moderate. Runoff is low to very high and the hazard of water erosion is slight to severe. The hazard of soil blowing is severe. The soils are moderately to very strongly alkaline (pH 7.9 - 9.6). They are very slightly to strongly saline (EC 2-16) and slightly to moderately sodic (SAR 5-30).
Characteristic taxonomic units are:
Shiprock SSA:
107-Tocito-Gullied land complex (Tocito part)
122-Blueflat-Notal Assoc. (Notal part)
160-Notal-Escavada-Riverwash assoc. (Notal part)
170-Notal sandy clay loam
177-Notal silty clay loam
200-Tocito loam
Other soils included are:
Table 4. Representative soil features
Surface texture (1) Clay loam
(2) Silty clay loam
(3) Loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Very slow to moderately slow Soil depth 60 in Surface fragment cover <=3" Not specified Surface fragment cover >3" Not specified Available water capacity
(0-40in)6 in Calcium carbonate equivalent
(0-40in)5 – 10 % Electrical conductivity
(0-40in)2 – 16 mmhos/cm Sodium adsorption ratio
(0-40in)5 – 30 Soil reaction (1:1 water)
(0-40in)7.9 – 9.6 Subsurface fragment volume <=3"
(Depth not specified)0 – 10 % Subsurface fragment volume >3"
(Depth not specified)Not specified Ecological dynamics
This ecological site has a plant community made up primarily of grasses, shrubs, and a small percentage of forbs. In the historic climax plant community, there are more warm-season grasses than cool-season grasses. The high sodium content in the soil determines many of the species that grow on the site.
Plant species most likely to invade or increase on this site when it deteriorates are black greasewood, Russian thistle, Powell's saltweed, and other annual weeds. When this site is continuously grazed yearlong, the desirable species will be replaced by less palatable plants. The sodium-adapted mound saltbush will increase as grass species decrease.State and transition model
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textState 1 submodel, plant communities
State 2 submodel, plant communities
State 3 submodel, plant communities
State 1
Reference StateCommunity 1.1
Reference Plant CommunityThis ecological site has a plant community made up primarily of grasses, shrubs, and a small percentage of forbs. In the historic climax plant community, there are more warm-season grasses than cool-season grasses. The high sodium content in the soil determines many of the species that grow on the site.
Plant species most likely to invade or increase on this site when it deteriorates are black greasewood, Russian thistle, Powell's saltweed, and other annual weeds. When this site is continuously grazed yearlong, the desirable species will be replaced by less palatable plants. The sodium-adapted mound saltbush will increase as grass species decrease.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 200 280 340 Shrub/Vine 10 30 200 Forb 10 30 40 Total 220 340 580 Figure 5. Plant community growth curve (percent production by month). NM0376 , R035XB016NM-Clay Loam Terrace (Sodic)-HCPC. R035XB016NM-Clay Loam Terrace (Sodic)-HCPC.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 6 6 7 6 6 5 11 14 12 12 8 7 Community 1.2
Native Shrubland with GrassesThis plant community includes many of the species in 1.1, but exhibits a marked increase in shrubs.
Pathway P1.1A
Community 1.1 to 1.2Season-long grazing providing little rest and recovery for preferred grazed plants during critical growing periods, coupled with high utilization.
Key drivers
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Precipitation (decadal scale)
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Wildlife grazing or browsing
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Food and fiber: livestock forage
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Wildlife forage
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Climate regulation: carbon cycling and storage
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Wildlife habitat
Pathway P1.2A
Community 1.2 to 1.1Prescribed grazing.
Conservation practices
Prescribed Grazing Key drivers
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Precipitation (decadal scale)
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Food and fiber: livestock forage
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Climate regulation: carbon cycling and storage
State 2
Native/Introduced Non-Native StateThis state includes a grass community that is dominated by non-native species.
Community 2.1
Non-Native Grassland with ShrubsThis phase is dominated by non-native grasses. It contains scattered shrubs.
Community 2.2
Shrubland with Non-Native GrassesThis phase is dominated by shrubs. Its grass community is dominated by non-native species.
Pathway P2.1A
Community 2.1 to 2.2Season-long grazing providing little rest and recovery for preferred grazed plants during critical growing periods, coupled with high utilization.
Key drivers
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Precipitation (decadal scale)
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Wildlife grazing or browsing
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Nutrient cycling
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Food and fiber: livestock forage
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Climate regulation: carbon cycling and storage
Pathway P2.2A
Community 2.2 to 2.1Prescribed grazing.
Conservation practices
Prescribed Grazing Key drivers
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Precipitation (decadal scale)
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Food and fiber: livestock forage
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Climate regulation: carbon cycling and storage
State 3
Shrub StateCommunity 3.1
Mixed Shrubs/AnnualsCommunity 3.2
Mound Saltbush/AnnualsPathway P3.1A
Community 3.1 to 3.2The mechanism for this pathway is unclear, and is a topic for future research.
Key drivers
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Precipitation (decadal scale)
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Climate regulation: carbon cycling and storage
Pathway P3.2A
Community 3.2 to 3.1The mechanism for this pathway is unclear, and is a topic for future research.
Conservation practices
Prescribed Grazing Key drivers
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Precipitation (decadal scale)
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Nutrient cycling
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Climate regulation: carbon cycling and storage
Transition T1A
State 1 to 2Season-long grazing providing little rest and recovery for preferred grazed plants during critical growing periods, coupled with high utilization.
Key drivers
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Precipitation (decadal scale)
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Wildlife grazing or browsing
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Livestock grazing or browsing
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Seed dispersal by livestock
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Climate
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Precipitation (annual scale)
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Food and fiber: livestock forage
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Wildlife forage
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Climate regulation: carbon cycling and storage
Transition T1B
State 1 to 3Season-long grazing providing little rest and recovery for preferred grazed plants during critical growing periods, coupled with high utilization.
Key drivers
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Precipitation (decadal scale)
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Wildlife grazing or browsing
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Livestock grazing or browsing
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Climate
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Precipitation (annual scale)
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Fire frequency
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Food and fiber: livestock forage
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Wildlife forage
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Climate regulation: carbon cycling and storage
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Wildlife habitat
Transition T2A
State 2 to 3Season-long grazing providing little rest and recovery for preferred grazed plants during critical growing periods, coupled with high utilization.
Key drivers
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Livestock grazing or browsing
Key ecosystem services affected
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Erosion control
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Nutrient cycling
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Food and fiber: livestock forage
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Climate regulation: carbon cycling and storage
Restoration pathway R3A
State 3 to 2Brush management.
Conservation practices
Brush Management Range Planting Prescribed Grazing Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 alkali sacaton 150–200 alkali sacaton SPAI Sporobolus airoides 150–200 – 2 galleta 25–50 James' galleta PLJA Pleuraphis jamesii 25–50 – 3 squirreltail 0–25 squirreltail ELEL5 Elymus elymoides 0–25 – 4 other perennial grasses 0–25 Grass, perennial 2GP Grass, perennial 0–25 – Forb5 Powell's saltweed 0–10 Powell's saltweed ATPO2 Atriplex powellii 0–10 – 6 perennial forbs 0–10 Forb, perennial 2FP Forb, perennial 0–10 – 7 annual forbs 0–5 Forb, annual 2FA Forb, annual 0–5 – Shrub/Vine8 mound saltbush 100–125 mound saltbush ATOB Atriplex obovata 100–125 – 9 black greasewood 5–25 greasewood SAVE4 Sarcobatus vermiculatus 5–25 – 10 Mojave seablite 0–15 Mojave seablite SUMO Suaeda moquinii 0–15 – 11 fourwing saltbush 0–25 fourwing saltbush ATCA2 Atriplex canescens 0–25 – 12 sickle saltbush 0–5 sickle saltbush ATFA Atriplex falcata 0–5 – 13 valley saltbush 0–5 valley saltbush ATCU Atriplex cuneata 0–5 – 14 other shrubs 0–15 Shrub (>.5m) 2SHRUB Shrub (>.5m) 0–15 – Table 7. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 8. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 9. Community 2.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 10. Community 3.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 11. Community 3.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
Competition between wildlife and cattle can be severe during all seasons. Plant community diversity is fair to good. This site provides important yearlong food and cover for wildlife. Brush management practices should maximize edge effect and allow for corridors to and from water.
Hydrological functions
This site normally receives approximately 7-10 inches annual precipitation. Most summer rainfall occurs as brief, sometimes heavy, thunderstorms. Slopes range from 0-5 percent. Runoff is low to very high, and the hazard of water erosion is low on soils with slopes <1 percent. As the slope increases to 5 percent, the potential for water erosion increases to very high. On sodic soils, erosion potential increases as sodium adsorbed on clay particles disperses and plugs soil pore spaces, thus decreasing water infiltration, percolation, and drainage.
Recreational uses
Wildlife observation, horseback riding, photography, and hiking can be enjoyed on this site. Care must be taken to prepare for hot, dry summers and cold winters.
Wood products
This site has no significant value for wood products.
Other products
This site is suitable for grazing by all classes of livestock during most seasons of the year. Planned grazing systems can be readily adapted to this site. This site is susceptible to wind erosion, particularly on overgrazed areas with little or no vegetation cover.
Supporting information
Inventory data references
The potential historic climax plant community has been determined by study of range relict areas or areas protected from excessive grazing. Trends in plant communities going from heavily grazed areas to lightly grazed areas, seasonal use pastures, and historical accounts have also been used.
Type locality
Location 1: San Juan County, NM Township/Range/Section T22N R16W S3 General legal description Great Bend Quad, Navajo Reservation, NM Contributors
David Trujillo
George Chavez
John Tunberg
Michael CarpinelliApproval
Kendra Moseley, 5/20/2025
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 04/30/2026 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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