Natural Resources
Conservation Service
Ecological site R046XS114MT
Shallow (Sw) RRU 46-S 13-19 PZ
Last updated: 7/19/2023
Accessed: 04/18/2024
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.
Associated sites
| R046XS104MT |
Silty (Si) RRU 46-S 13-19 PZ |
|---|---|
| R046XS106MT |
Sandy (Sy) RRU 46-S 15-19 PZ |
| R046XS115MT |
Very Shallow (VSw) RRU 46-S 13-19 PZ |
Similar sites
| R046XS619MT |
Shallow Clay (SwC) RRU 46-S 13-16 PZ The Shallow Clay site varies by texture. |
|---|---|
| R046XS106MT |
Sandy (Sy) RRU 46-S 15-19 PZ The Sandy site varies by being over 20 inches deep and having significantly more production and plant cover. |
| R046XS104MT |
Silty (Si) RRU 46-S 13-19 PZ The Silty site varies by being over 20 inches deep and having significantly more production and plant cover. |
| R046XS115MT |
Very Shallow (VSw) RRU 46-S 13-19 PZ The Very Shallow site is less than 10 inches deep, or has a water holding capacity of 2 inches or less. |
Table 1. Dominant plant species
| Tree |
Not specified |
|---|---|
| Shrub |
Not specified |
| Herbaceous |
(1) Pseudoroegneria spicata |
Physiographic features
This ecological site occurs on nearly level to very steep plains, shoulders and side slopes of hills, ridgetops, and bedrock escarpments, and often occurs in complex with other ecological sites. This site occurs on all slopes and exposures. Aspect may be significant, especially on steep and very steep slopes. Variations in plant community composition and production can result due to aspect. Runoff and potential for water erosion are important features of this site. The amount of exposed rock outcrop tends to increase as slopes increase.
Table 2. Representative physiographic features
| Landforms |
(1)
Hill
(2) Escarpment |
|---|---|
| Flooding frequency | None |
| Ponding frequency | None |
| Slope | 60% |
| Water table depth | 60 in |
| Aspect | Aspect is not a significant factor |
Climatic features
See Climatic Data Sheet for more details (Section II of the Field Office Technical Guide) or reference the following climatic web site: http://www.wrcc.sage.dri.edu/ .
Table 3. Representative climatic features
| Frost-free period (characteristic range) | 49-96 days |
|---|---|
| Freeze-free period (characteristic range) | 105-122 days |
| Precipitation total (characteristic range) | 14-18 in |
| Frost-free period (actual range) | 47-99 days |
| Freeze-free period (actual range) | 104-125 days |
| Precipitation total (actual range) | 13-18 in |
| Frost-free period (average) | 76 days |
| Freeze-free period (average) | 114 days |
| Precipitation total (average) | 16 in |
Figure 2. Monthly precipitation range
Figure 3. Monthly minimum temperature range
Figure 4. Monthly maximum temperature range
Figure 5. Monthly average minimum and maximum temperature
Figure 6. Annual precipitation pattern
Figure 7. Annual average temperature pattern
Climate stations used
-
(1) JOLIET [USC00244506], Joliet, MT
-
(2) COLUMBUS [USC00241938], Columbus, MT
-
(3) BIG TIMBER [USC00240780], Big Timber, MT
-
(4) MELVILLE 4 W [USC00245603], Big Timber, MT
-
(5) MARTINSDALE 3 NNW [USC00245387], Martinsdale, MT
-
(6) NYE 2 [USC00246190], Fishtail, MT
Influencing water features
No influencing water features.
Soil features
These soils are 10 to 20 inches deep to hard rock or soft beds. Parent material can be granite, sandstone, siltstone, or limestone. Few roots penetrate deeper than 20 inches. Surface textures are mainly silt loam, loam, sandy loam, fine sandy loam, loamy fine sand, and very fine sandy loam. Available Water Holding Capacity to 20" is 2 to 4 inches.
Table 4. Representative soil features
| Surface texture |
(1) Gravelly silt loam (2) Loam (3) Sandy loam |
|---|---|
| Drainage class | Well drained to somewhat excessively drained |
| Permeability class | Moderate to moderately rapid |
| Soil depth | 10 – 20 in |
| Available water capacity (0-40in) |
4 in |
| Electrical conductivity (0-40in) |
Not specified |
| Soil reaction (1:1 water) (0-40in) |
6.6 – 8.4 |
| Subsurface fragment volume <=3" (Depth not specified) |
35% |
Ecological dynamics
This site developed under Northern Rocky Mountain Foothills climatic conditions, which included the natural influence of large herbivores and occasional fire. The plant community upon which interpretations are primarily based is the Historic Climax Plant Community (HCPC). This community is described as a reference to understand the original potential of this site, and is not always considered to be the management goal for every acre of rangeland.
The following descriptions should enable the landowner or manager to better understand which plant communities occupy their land, and assist with setting goals for vegetation management. It can also be useful to understand the environmental and economic values of each plant community.
This site is considered moderately resilient to disturbance as it has only moderate soil limitations for plant growth. Changes may occur to the Historic Climax Plant Community due to management actions and/or climatic conditions. Under continued adverse impacts, a moderate decline in vegetative vigor and composition will occur. Under favorable vegetative management treatments the site can more readily return to the Historic Climax Plant Community (HCPC).
Continual adverse impacts to the site over a period of years results in a departure from the HCPC, with a decrease of the taller, more palatable species such as bluebunch wheatgrass, spike fescue, tall needlegrasses, plains muhly, purple and white prairieclovers, and dotted gayfeather. These plants will be replaced by Idaho fescue, needleandthread, thickspike/western wheatgrass, threadleaf sedge, Cusick bluegrass, Parry danthonia, various other increaser short grasses, and increaser forbs. Shrubs such as mountain big sagebrush can occur, sometimes related to fire occurance and frequency. Continued deterioration results in increased amounts of red or Fendler’s threeawn and fringed sagewort.
Plants that are not a part of the climax community that are most likely to invade are cheatgrass and Japanese bromes, six-weeks fescue, broom snakeweed, thistles. There are several noxious weeds that are also likely to invade this site including spotted knapweed, leafy spurge, dalmation toadflax, and sulphur cinquefoil.
State and transition model
Figure 8. State and Transition Model
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
Ecosystem states
State 1 submodel, plant communities
State 2 submodel, plant communities
State 3 submodel, plant communities
State 4 submodel, plant communities
State 5 submodel, plant communities
State 6 submodel, plant communities
State 1
Tall and Medium Grasses/Forbs/Shrubs
Community 1.1
Tall and Medium Grasses/Forbs/Shrubs
This is the interpretive plant community and is considered to be the Historic Climax Plant Community (HCPC) for this site. This plant community contains a high diversity of tall and medium height, cool and warm season grasses and grasslikes (bluebunch wheatgrass, tall needlegrasses, spike fescue, plains muhly, Idaho fescue, needleandthread and, thickspike or Western wheatgrass), and short grasses and sedges (Cusick bluegrass, Parry danthonia, Sandberg bluegrass, prairie junegrass, threadleaf and needleleaf sedge). There are abundant forbs (dotted gayfeather, prairie clovers) which occur in smaller percentages. This plant community is well adapted to the Northern Rocky Mountain foothills climatic conditions. The diversity in plant species allows for drought tolerance. Individual species can vary greatly in production depending on growing conditions (timing and amount of precipitation, and temperature). This plant community is well suited to managed livestock grazing and provides diverse habitat for many wildlife species. Plants on this site have strong, healthy root systems that allow production to increase significantly with favorable moisture conditions. This plant community provides for soil stability and a properly functioning hydrologic cycle. Abundant plant litter is available for soil building and moisture retention. Plant litter is properly distributed with very little movement off-site and natural plant mortality is very low. The soils associated with this site provide a limited soil-water-plant relationship.
Figure 9. 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 | 810 | 990 | 1170 |
| Shrub/Vine | 54 | 132 | 234 |
| Forb | 54 | 99 | 156 |
| Total | 918 | 1221 | 1560 |
Table 6. Ground cover
| Tree foliar cover | 0% |
|---|---|
| Shrub/vine/liana foliar cover | 0-5% |
| Grass/grasslike foliar cover | 75-90% |
| Forb foliar cover | 1-10% |
| Non-vascular plants | 0-5% |
| 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. Soil surface cover
| Tree basal cover | 0% |
|---|---|
| Shrub/vine/liana basal cover | 0-2% |
| Grass/grasslike basal cover | 15-20% |
| Forb basal cover | 1-2% |
| Non-vascular plants | 0-1% |
| Biological crusts | 0% |
| Litter | 40-60% |
| Surface fragments >0.25" and <=3" | 0% |
| Surface fragments >3" | 10-15% |
| Bedrock | 0% |
| Water | 0% |
| Bare ground | 0-10% |
State 2
Medium and Short Grasses, Forbs
Community 2.1
Medium and Short Grasses, Forbs
Early stages of degradation, including non-prescribed grazing, will tend to change the HCPC to a community dominated by medium and short grasses such as Idaho fescue, needleandthread (mainly 15 inches MAP or less), thickspike/western wheatgrass, Cusick bluegrass, Parry danthonia, Sandberg bluegrass, and prairie junegrass. Most of the taller and more palatable grasses (bluebunch wheatgrass, tall needlegrasses, spike fescue, plains muhly) will still be present but in smaller amounts. There may be an increase in the amount of some shrubs. Palatable and nutritious forbs will be replaced by less desirable and more aggressive species such as goldenpea. This plant community will readily respond to improved grazing management, but a significant amount of time can be necessary to move it toward a higher successional stage and a more productive plant community similar to community 1. Biomass production and litter become slightly reduced on the site with Community 2 as the taller grasses become replaced by shorter ones. Evapotranspiration tends to increase, moisture retention is reduced, and soil surface temperatures increase. Some natural ecological processes will be altered. These plant communities provide for moderate soil stability. Increased amounts of bare ground can result in undesirable species invading. Common invaders can include spotted knapweed, leafy spurge, dalmation toadflax, and sulphur cinquefoil.
State 3
Sedge, Mid and Short Increaser Grasses, Increaser Forbs, Fringed Sagewort
Community 3.1
Sedge, Mid and Short Increaser Grasses, Increaser Forbs, Fringed Sagewort
With continued degradation to community 2, the site will become dominated by species such as threadleaf sedge, short grasses such as prairie junegrass and Sandberg bluegrass, Idaho fescue, needleandthread, thickspike or western wheatgrass, fringed sagewort, and increaser forbs such as arrowleaf balsamroot and goldenpea. There may still be remnant amounts of some of the late-seral species such as bluebunch wheatgrass, spike fescue, and green/Columbia needlegrass present. The taller grasses will occur only occasionally. Palatable forbs will be mostly absent. In some situations, non-native grasses such as Kentucky bluegrass may also occur, sometimes comprising up to about 50 percent of the composition. Plant community 3 is often less productive than 1 or 2. The lack of litter and short plant heights result in higher soil temperatures, poor water infiltration rates, and higher evapotranspiration rates, thus eventually favoring species that are more adapted to drier conditions. These communities have lost many of the attributes of a healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling and energy flow. This community will respond positively to improved grazing management, but significant economic inputs along with a significant amount of time are usually required to move it toward a higher successional stage and a more productive plant community. There are limitations to using mechanical treatment on this site due to the shallow soils
State 4
Sedge, Mid and Short Increaser Grasses, Increaser Forbs, Fringed Sagewort, Sagebrush
Community 4.1
Sedge, Mid and Short Increaser Grasses, Increaser Forbs, Fringed Sagewort, Sagebrush
Continued degradation of this site where it receives slightly better moisture causes plant community 2 to deteriorate to one similar to community number 3, except that mountain big sagebrush may become abundant. Given the right circumstances, non-native grasses such as Kentucky or Canada bluegrass can also occupy this site. If degradation continues, they will continue to increase and replace other native species. Fire can cause this community to move to one similar to No. 3. Fire, with prescribed grazing, may also move this community towards one similar to number 2. Other forms of brush management may also do the same. However, mountain big sagebrush communities tend to return unless fire or other treatments are repeated periodically. Plant communities 3 & 4 are often less productive than 1 or 2. The lack of litter and short plant heights result in higher soil temperatures, poor water infiltration rates, and higher evapotranspiration rates, thus eventually favoring species that are more adapted to drier conditions. These communities have lost many of the attributes of a healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling and energy flow. Communities 3 and 4 will respond positively to improved grazing management, but significant economic inputs and time will usually also be needed to move them toward a higher successional stage. Once plants such as mountain big sagebrush become established, they are very difficult to remove and replace by grazing management alone. Additionally, the chances for success are significantly reduced.
State 5
Half shrubs, Short grasses, Annuals, Weedy Forbs, Threeawns
Community 5.1
Half shrubs, Short grasses, Annuals, Weedy Forbs, Threeawns
Further deterioration of community 3 results in a plant community dominated by many increaser short grasses such as prairie junegrass and Sandberg bluegrass. will be abundant undesirable plants such as red threeawn, fringed sagewort, broom snakeweed, weedy forbs (e.g., pussytoes and thistles), annuals such as cheatgrass and Japanese bromes and sixweeks fescue, threadleaf sedge, and yucca. This plant community produces less usable forage than the others described. The continuation of the downward trend and degradation of this site has resulted in higher soil surface temperatures, reduced water infiltration, and higher evapotranspiration. This has resulted in plant species that are more adapted to drier conditions, such as blue grama. Most of the attributes of a healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling and energy flow, have been lost.
State 6
Sagebrush, Half shrubs, Increaser short grasses, Weedy forbs, Annual grasses
Community 6.1
Sagebrush, Half shrubs, Increaser short grasses, Weedy forbs, Annual grasses
As degradation to Community 4 continues, the site will become dominated by mountain big sagebrush. Fringed sagewort and broom snakeweed become abundant. Short grasses and sedges have replaced the taller grasses, although there may still be remnant individuals of Idaho fescue, needleandthread, and thickspike/western wheatgrass scattered through the community, often under the sagebrush plants. Plains pricklypear cactus, weedy forbs, and annual species become more common and aggressive weedy grasses such as red threeawn become abundant. Fire, along with prescribed grazing, may move this community back towards one similar to number 4 by reducing the mountain big sagebrush component, although the probability of success can be somewhat diminished, depending on the composition of the rest of the plant community. These last two communities can respond positively to improved grazing management, but it will take additional inputs to move either of them towards communities similar in production and composition to others that have been described. Extended periods of rest followed by prescribed grazing, may help return this site to a community resembling 2, 3, or 4. However, because of the shallow soils (and sometimes, steeper slopes) associated with this ecological site, practices such as mechanical treatment or seeding are generally not feasible nor recommended.
Additional community tables
Table 8. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (lb/acre) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Shrub/Vine
|
||||||
| 1 | Shrubs and Half-shrubs | 54–234 | ||||
| Shrub, broadleaf | 2SB | Shrub, broadleaf | 0–78 | – | ||
| silver sagebrush | ARCAV2 | Artemisia cana ssp. viscidula | 0–78 | – | ||
| prairie sagewort | ARFR4 | Artemisia frigida | 0–78 | – | ||
| mountain big sagebrush | ARTRV | Artemisia tridentata ssp. vaseyana | 0–78 | – | ||
| Wyoming big sagebrush | ARTRW8 | Artemisia tridentata ssp. wyomingensis | 0–78 | – | ||
| broom snakeweed | GUSA2 | Gutierrezia sarothrae | 0–78 | – | ||
| prairie rose | ROARS | Rosa arkansana var. suffulta | 0–78 | – | ||
|
Grass/Grasslike
|
||||||
| 2 | Grasses and Sedges | 810–1170 | ||||
| bluebunch wheatgrass | PSSP6 | Pseudoroegneria spicata | 432–1092 | – | ||
| spike fescue | LEKI2 | Leucopoa kingii | 0–390 | – | ||
| Idaho fescue | FEID | Festuca idahoensis | 54–234 | – | ||
| needle and thread | HECOC8 | Hesperostipa comata ssp. comata | 0–124 | – | ||
| prairie Junegrass | KOMA | Koeleria macrantha | 54–124 | – | ||
| Sandberg bluegrass | POSE | Poa secunda | 54–124 | – | ||
| Grass, perennial | 2GP | Grass, perennial | 0–124 | – | ||
| blue grama | BOGR2 | Bouteloua gracilis | 54–124 | – | ||
| needleleaf sedge | CADU6 | Carex duriuscula | 54–124 | – | ||
| threadleaf sedge | CAFI | Carex filifolia | 54–124 | – | ||
| plains reedgrass | CAMO | Calamagrostis montanensis | 54–124 | – | ||
| thickspike wheatgrass | ELLAL | Elymus lanceolatus ssp. lanceolatus | 0–78 | – | ||
| western wheatgrass | PASM | Pascopyrum smithii | 0–78 | – | ||
| plains muhly | MUCU3 | Muhlenbergia cuspidata | 0–78 | – | ||
| green needlegrass | NAVI4 | Nassella viridula | 0–39 | – | ||
| Letterman's needlegrass | ACLE9 | Achnatherum lettermanii | 0–39 | – | ||
| Columbia needlegrass | ACNEN2 | Achnatherum nelsonii ssp. nelsonii | 0–39 | – | ||
| western needlegrass | ACOCO | Achnatherum occidentale ssp. occidentale | 0–39 | – | ||
| purple threeawn | ARPU9 | Aristida purpurea | 0–1 | – | ||
|
Forb
|
||||||
| 3 | Forbs | 54–156 | ||||
| Forb, perennial | 2FP | Forb, perennial | 0–78 | – | ||
| western yarrow | ACMIO | Achillea millefolium var. occidentalis | 0–78 | – | ||
| pale agoseris | AGGL | Agoseris glauca | 0–78 | – | ||
| onion | ALLIU | Allium | 0–78 | – | ||
| pussytoes | ANTEN | Antennaria | 0–78 | – | ||
| aster | ASTER | Aster | 0–78 | – | ||
| milkvetch | ASTRA | Astragalus | 0–78 | – | ||
| balsamroot | BALSA | Balsamorhiza | 0–78 | – | ||
| prairie clover | DALEA | Dalea | 11–78 | – | ||
| Bonneville shootingstar | DOCO | Dodecatheon conjugens | 0–78 | – | ||
| yellow fritillary | FRPU2 | Fritillaria pudica | 0–78 | – | ||
| old man's whiskers | GETR | Geum triflorum | 0–78 | – | ||
| sticky purple geranium | GEVI2 | Geranium viscosissimum | 11–78 | – | ||
| dotted blazing star | LIPU | Liatris punctata | 11–78 | – | ||
| western stoneseed | LIRU4 | Lithospermum ruderale | 0–78 | – | ||
| desertparsley | LOMAT | Lomatium | 0–78 | – | ||
| leafy wildparsley | MUDI | Musineon divaricatum | 0–78 | – | ||
| locoweed | OXYTR | Oxytropis | 0–78 | – | ||
| beardtongue | PENST | Penstemon | 0–78 | – | ||
| spiny phlox | PHHO | Phlox hoodii | 0–78 | – | ||
| scurfpea | PSORA2 | Psoralidium | 0–78 | – | ||
| cutleaf anemone | PUPAM | Pulsatilla patens ssp. multifida | 0–78 | – | ||
| prairie thermopsis | THRH | Thermopsis rhombifolia | 0–78 | – | ||
| American vetch | VIAM | Vicia americana | 0–78 | – | ||
| deathcamas | ZIGAD | Zigadenus | 0–1 | – | ||
| larkspur | DELPH | Delphinium | 0–1 | – | ||
Interpretations
Animal community
Livestock Grazing Interpretations: Managed livestock grazing is suitable on this site as it has
the potential to produce a limited amount of high quality forage. Grazing must be managed carefully on this site to be sure livestock drift onto the better, more productive sites is not excessive. Management objectives should include maintenance or improvement of the plant community. Shorter grazing periods and adequate re-growth after grazing are recommended for plant maintenance and recovery. Heavy stocking and season-long use of this site can be detrimental and will alter the plant community composition and production over time.
Using shorter grazing periods and providing for adequate re-growth after grazing are recommended for plant maintenance, health, and recovery. Continual over stocking and season-long use of this site can be detrimental and will alter the plant composition and production over time. The result will be plant communities that resemble numbers 3 and 4, depending on how long this grazing management is used as well as other circumstances such as weather conditions and fire frequency.
Whenever Plant Community 2 (medium and short grasses) occurs, grazing management strategies that will prevent further degradation need to be implemented. This community is still stable, productive, and healthy provided it receives proper management. It will respond fairly quickly to improved grazing management, including increased growing season rest of key forage plants. Grazing management alone can usually move this back towards the potential / historic climax community.
Plant communities 3 and 4 are the result of long-term, heavy, continuous grazing and/or annual, early spring seasonal grazing. Repeated heavy early spring grazing, especially during stem elongation (generally mid May through mid June), can also have detrimental affects on the taller, key forage species. Repeated spring grazing depletes stored carbohydrates, resulting in weakening and eventual death of the cool season tall and medium grasses. This plant community can occur throughout the pasture, on spot grazed areas, and around water sources where season-long grazing patterns occur.
Plant Communities 5 and 6 have a high percentage of aggressive, less-desirable species. Once these have become established, it is significantly more difficult using grazing management alone to restore the site to one that resembles the HCPC. It becomes critical at this point to implement a grazing strategy that will restore the stability and health of the site. Additional rest, sometimes for the growing season, or more probable for a full year or more, is often necessary for re-establishment of the desired species. There are limitations to using mechanical treatment on this site due to the shallow soils.
Calculating Safe Stocking Rates: Proper stocking rates should be incorporated into a grazing
management strategy that protects the resource, maintains or improves rangeland health, and is consistent with management objectives. Safe stocking rates will be based on useable forage production, and should consider ecological condition and trend of the site, and past grazing use history.
Calculations used to determine a safe stocking rate are based on the amount of useable forage available,
taking into account the harvest efficiency of the animal and the grazing strategy to be implemented. Average annual production must be measured or estimated to properly assess useable forage production and stocking rates.
Stocking rates are calculated from average forage production values using a 25% Harvest Efficiency factor for preferred and desirable plants, and 10% Harvest Efficiency for less desirable species. AUM calculations are based on 915 pounds (air-dry) per animal unit month (AUM) for a 1,000-pound cow with calf up to 4 months. No adjustments have been made for site grazability factors, such as steep slopes, site inaccessibility, or distance to drinking water.
The following is an example of how to calculate the recommended stocking rate. This example does not use production estimates from this specific ecological site. You will need to adjust the annual production values and run the calculations using total annual production values from the ecological sites encountered on each individual ranch/pasture. Before making specific recommendations, an on-site evaluation must be made.
Example of total annual production amounts by type of year:
Favorable years = 2200 lbs/acre
Normal years = 1480 lbs/acre
Unfavorable years = 1200 lbs/acre
It is recommended that on slopes of 30% or less, stocking rate should be derived from the total annual production pounds minus 500 pounds for residual dry matter and 25% harvest efficiency. On slopes over 30%, stocking rate is derived from total annual production pounds minus 800 pounds for residual dry matter and 25% harvest efficiency. Refer to the NRCS National Range and Pasture Handbook for a list of Animal Unit Equivalents.
Sample Calculations using Favorable Year production amounts:
< 30% slopes: AUM/AC = [(2200-500)(0.25)]/915 lbs/month for one AU = 0.46 AUM/AC
AC/AUM = (1.0 AU)/(0.46AUM/AC) = 2.2 AC/AUM
> 30% slopes: AUM/AC = [(2200-800)(0.25)]/915 lbs/month for one AU = 0.38 AUM/AC
AC/AUM = (1.0 AU)/(0.38 AU! M/AC) = 2.6 AC/AUM
NOTE: 915 lbs/month for one Animal Unit is used as the baseline for maintenance requirements. This equates to 30 lbs/day of air-dry forage (1200 lb cow at 2.5% of body weight).
Hydrological functions
The runoff potential for this site is low to moderate, depending on slope and ground cover/health. Runoff curve numbers generally range from 78 to 90. The soils associated with this ecological site are generally in Hydrologic Soil Group C. The infiltration rates for these soils will normally be moderate to moderately rapid.
Good hydrologic conditions exist on rangelands if plant cover (grass, litter, and brush canopy) is greater than 70%. Fair conditions exist when cover is between 30 and 70%, and poor conditions exist when cover is less than 30%. Sites in high similarity to HCPC (Plant Communities 1a, 1b, 1c, and 2) generally have enough plant cover and litter to optimize infiltration, minimize runoff and erosion, and have a good hydrologic condition. The deep root systems of the potential vegetation help maintain or increase infiltration rates and reduce runoff.
Sites in low similarity (Plant Communities 5 and 6) are generally considered to be in poor hydrologic condition as the majority of plant cover is from shallow-rooted species such as blue grama, annual grasses, and shrubs.
Erosion is minor for sites in high similarity. Rills and gullies should not be present. Water flow patterns, if present, will be barely observable. Plant pedestals are essentially non-existent. Plant litter remains in place and is not moved by erosion. Soil surfaces should not be compacted or crusted. Plant cover and litter helps retain soil moisture for use by the plants. Maintaining a healthy stand of perennial vegetation will optimize the amount of precipitation that is received. (Reference: Engineering Field Manual, Chapter 2 and Montana Supplement 4).
Recreational uses
This site provides some recreational opportunities for hiking,
horseback riding, big game and upland bird hunting. The forbs have flowers that appeal to photographers.
This site provides valuable open space and visual aesthetics. Caution should be used during wet weather
periods.
Wood products
None.
Supporting information
Contributors
Robert Leinard; Barbara Gibbons; Matt Ricketts; Peter Husby, Jon Siddoway
Approval
Kirt Walstad, 7/19/2023
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) | G. Petersen |
|---|---|
| Contact for lead author | grant.petersen@usda.gov |
| Date | 03/01/2020 |
| Approved by | Kirt Walstad |
| Approval date | |
| Composition (Indicators 10 and 12) based on | Annual Production |
Indicators
-
Number and extent of rills:
Rills are, generally, not present in the reference condition. If present, they will be short and inconspicuous on steep slopes exceeding 20%. -
Presence of water flow patterns:
Water flow patterns are, generally, not present in the reference condition but may be present on the steep, south facing slopes when runoff exceeds infiltration. These patterns will be short and infrequent across gentle slopes and increasingly more common on steeper slopes. -
Number and height of erosional pedestals or terracettes:
Pedestals are typically not evident in the reference condition. If present, they will be on slopes greater than 25 percent and associated with waterflow patterns. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground is 5-10%; however steeper, southerly aspects may express slightly higher bare ground of 10-15%. -
Number of gullies and erosion associated with gullies:
Gullies are not present in the reference condition. -
Extent of wind scoured, blowouts and/or depositional areas:
Wind scoured, or depositional areas are not evident in the reference condition. -
Amount of litter movement (describe size and distance expected to travel):
Litter movement is infrequent across gentle slopes and increasingly more common on steeper slopes. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
The average soil stability rating is 4-6 under plant canopies and plant interspaces. The A horizon is 2-4” inches thick. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Soil Structure at the surface is typically moderate medium granular to weak fine subangular blocky. A Horizon should be 2-4 inches thick with color, when wet, typically ranging in Value of 5 or less and Chroma of 4 or less.
Local geology may affect color, it is important to reference the Official Series Description (OSD) for characteristic range. https://soilseries.sc.egov.usda.gov/osdname.aspx -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Infiltration of the Shallow ecological site is moderate to moderately rapid. The site is well drained. An even distribution of mid stature grasses, 65-75% of site production, cool season rhizomatous grasses (10-15%) with shortgrass (15-20%), forbs (5-10), shrubs (10-15%) and trees/tall shrubs (0-1%) -
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
A compaction layer is not present in the reference condition. -
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:
Mid-statured, cool season, perennial bunchgrasses (Primarily bluebunch wheatgrass, Columbia needlegrass, spike fescue)Sub-dominant:
Shortgrass grasses & Grasslikes (Idaho fescue, needle and thread) = Forbs ≥ Shrubs >> trees/tall shrubsOther:
Additional:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Mortality in herbaceous species is not evident. Species with bunch growth forms may have some natural mortality in centers is 3% or less. -
Average percent litter cover (%) and depth ( in):
Total litter cover ranges from 40-60%. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Average annual production is 1400. Low: 1225 High 1550. Production varies based on effective precipitation and natural variability of soil properties for this ecological site. -
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:
Potential invasive (including noxious) species (native and non-native). Invasive species on this ecological site include (but not limited to) smooth brome, sulphur cinquefoil, dandelion, annual brome spp., spotted knapweed, salsify, leafy spurge, and ventenata,
Native species such as Rocky Mountain juniper, ponderosa pine, limber pine, Douglas fir, creeping juniper, lupine, broom snakeweed, Sandberg bluegrass, etc. when their populations are significant enough to affect ecological function, indicate site condition departure. -
Perennial plant reproductive capability:
In the reference condition, all plants are vigorous enough for reproduction either by seed or rhizomes in order to balance natural mortality with species recruitment.
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The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.
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