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Natural Resources
Conservation Service
Ecological site R046XN255MT
Stony (St) RRU 46-N 13-19 PZ
Last updated: 7/19/2023
Accessed: 08/16/2024
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.
Associated sites
R046XN247MT |
Clayey (Cy) RRU 46-N 13-19 PZ |
---|---|
R046XN248MT |
Overflow (Ov) RRU 46-N 13-19 PZ |
R046XN249MT |
Sandy (Sy) RRU 46-N 13-19 PZ |
R046XN252MT |
Silty (Si) RRU 46-N 13-19 PZ |
R046XN594MT |
Silty Steep (SiStp) RRU 46-N 13-19 PZ |
Similar sites
R046XN252MT |
Silty (Si) RRU 46-N 13-19 PZ These sites differ by not being covered by stones, or if there are surface stones present, they are less abundant (Class 1 or 2 stoniness). |
---|---|
R046XN247MT |
Clayey (Cy) RRU 46-N 13-19 PZ These sites differ by not being covered by stones, or if there are surface stones present, they are less abundant (Class 1 or 2 stoniness). |
R046XN249MT |
Sandy (Sy) RRU 46-N 13-19 PZ These sites differ by not being covered by stones, or if there are surface stones present, they are less abundant (Class 1 or 2 stoniness). |
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 strongly sloping plains, terraces, and fans. The slopes range from 0–15%, but are mainly less than 8%. This site occurs on all exposures. Aspect is not significant.
Table 2. Representative physiographic features
Landforms |
(1)
Plain
(2) Fan (3) Terrace |
---|---|
Flooding frequency | None |
Ponding frequency | None |
Slope | 15% |
Water table depth | 40 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) | 57-84 days |
---|---|
Freeze-free period (characteristic range) | 109-120 days |
Precipitation total (characteristic range) | 15-17 in |
Frost-free period (actual range) | 37-90 days |
Freeze-free period (actual range) | 101-122 days |
Precipitation total (actual range) | 14-17 in |
Frost-free period (average) | 69 days |
Freeze-free period (average) | 114 days |
Precipitation total (average) | 16 in |
Figure 1. Monthly precipitation range
Figure 2. Monthly minimum temperature range
Figure 3. Monthly maximum temperature range
Figure 4. Monthly average minimum and maximum temperature
Figure 5. Annual precipitation pattern
Figure 6. Annual average temperature pattern
Climate stations used
-
(1) BABB 6 NE [USC00240392], Babb, MT
-
(2) AUGUSTA [USC00240364], Augusta, MT
-
(3) CASCADE 5 S [USC00241552], Cascade, MT
-
(4) ROGERS PASS 9 NNE [USC00247159], Wolf Creek, MT
Influencing water features
No influencing water features.
Soil features
These soils form on alluvium, colluvium, residuum, or eolian deposits. They are loams, silt loams, very fine sandy loams, sandy loams, clay loams or sandy clay loams more than 20 inches deep having stones or boulders covering up to about 15% of the surface (Class 3 Stoniness). They include soils that have two inches or more of one of these textures over a clayey (argillic) subsoil. The presence of the surface stones interferes with the use of surface tillage implements, but usually has mimimal impact on production and species composition. Available Water Holding Capacity to a 40 inch depth is mostly about 8 inches.
Table 4. Representative soil features
Surface texture |
(1) Loam (2) Silt loam (3) Sandy loam |
---|---|
Drainage class | Moderately well drained to well drained |
Permeability class | Moderate |
Soil depth | 20 in |
Available water capacity (0-40in) |
5 – 8 in |
Electrical conductivity (0-40in) |
Not specified |
Subsurface fragment volume >3" (Depth not specified) |
5% |
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 highly resilient to disturbance as it has very few 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 to extreme decline in vegetative vigor and composition will occur. Under favorable vegetative management treatments this 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 rough fescue, bluebunch wheatgrass, green/Columbia needlegrasses, and porcupinegrass. These plants will typically be replaced by a mixture of medium and short grasses and sedges, including Idaho fescue, thickspike/western wheatgrass, needleandthread, Sandberg bluegrass, prairie junegrass, threadleaf sedge, and several species of more aggressive, less desirable forbs. Certain non-native species such as Kentucky or Canada bluegrass or common timothy can occupy this site, depending on circumstances and opportunity.
Continued deterioration to the community results in an abundance of short grasses such as prairie junegrass, Sandberg bluegrass, and oatgrasses, along with several species of weedy forbs.
Plants that are not a part of the Historic Climax Plant Community that are most likely to invade are annual grasses (cheatgrass, Japanese brome), and annual and biennial forbs. Leafy spurge, knapweeds, sulphur cinquefoil, and dalmation toadflax are potential noxious weed invaders on this site.
Long-term non-use (>3 years) combined with the absence of fire will result in excessive litter and decadent plants in the bunchgrass communities.
State and transition model
![Model diagram](https://edit.jornada.nmsu.edu/uploads/med/es/es/2341.jpg)
Figure 7. 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 7 submodel, plant communities
State 1
Tall and Medium Grasses, Forbs
Community 1.1
Tall and Medium Grasses, Forbs
This is the interpretive plant community and is considered to be the Historic Climax Plant Community or Potential Plant Community for this site. This plant community contains a high diversity of tall and medium height, cool season grasses (rough fescue, bluebunch wheatgrass, Idaho fescue, green/Columbia needlegrass, porcupinegrass, mountain brome) and short grasses (Cusick and Sandberg bluegrass, Parry danthonia, and prairie junegrass). There are abundant forbs (geraniums, mountain dandelion) 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 (i.e., timing and amount of precipitation, and temperature). It 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 favorable soil-water-plant relationship.
Figure 8. 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 | 975 | 1265 | 1490 |
Forb | 0 | 158 | 370 |
Shrub/Vine | 0 | 40 | 95 |
Total | 975 | 1463 | 1955 |
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 | 17-21% |
Forb basal cover | 1-3% |
Non-vascular plants | 0-2% |
Biological crusts | 0% |
Litter | 40-60% |
Surface fragments >0.25" and <=3" | 0% |
Surface fragments >3" | 15-25% |
Bedrock | 0% |
Water | 0% |
Bare ground | 0-5% |
State 2
Medium and Short Grasses, Sedge, and Increaser Forbs
Community 2.1
Medium and Short Grasses, Sedge, and Increaser Forbs
Early stages of degradation, including non-prescribed grazing, will tend to change the HCPC to a community dominated by medium and short grasses and sedges such as Idaho fescue, needleandthread (mainly 15 inches MAP or less), thickspike / western wheatgrass, threadleaf sedge, prairie junegrass Cusick and Sandberg bluegrass, and spike oatgrass. Most of the taller and more palatable plants (bluebunch wheatgrass, rough fescue, tall needlegrasses, porcupinegrass) will still be present but in smaller amounts. There may be an increase in the amount of some shrubs, such as shrubby cinquefoil. Palatable and nutritious forbs will be replaced by less desirable and more aggressive species such as lupine and stoneseed.
State 3
Medium and Short Grasses, Forbs, Non-Native Grasses
Community 3.1
Medium and Short Grasses, Forbs, Non-Native Grasses
Given the right circumstances and opportunity, non-native grasses such as Kentucky/Canada bluegrass or common timothy will become established on this ecological site. In this situation, slight degradation in the historical climax plant community results in a plant community similar to #2, except that it will also have these non native plants as minor components. If further degradation continues, these species will continue to increase and replace other, more desirable native species. Biomass production and litter become slightly reduced on the site with Communities 2 and 3, as the taller grasses become replaced by shorter ones, especially the non-native grasses. 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. These plant communities (2 & 3) will readily respond to improved grazing management, but a significant amount of time can be necessary to move them toward a higher successional stage and a more productive plant community similar to community 1. The following plant communities are the result of long-term, heavy, continuous season long grazing and/or heavy, annual, early spring grazing. Repeated spring grazing depletes stored carbohydrates, resulting in weakening and eventual death of the cool season tall and medium grasses. They can occur throughout the pasture, on spot grazed areas, and near water sources where season-long grazing patterns occur. It is critical at this point to consider implementing a change in grazing management to prevent further degradation to any of the following plant communities and minimize the increase of less desirable and non native species. Once any of the following communities become established, the potential to return to communities 1, 2, or 3 is reduced and often requires a significant amount of time along with economic inputs.
State 4
Idaho Fescue, Short Grasses, Sageworts, Forbs
Community 4.1
Idaho Fescue, Short Grasses, Sageworts, Forbs
With continued heavy disturbance on community 2, the site will become dominated by short increaser species such as Idaho fescue, thickspike or western wheatgrass, Parry danthonia, prairie junegrass, sedges, needleandthread (15 inches MAP or less), fringed and/or cudweed sagewort, and perennial forbs such as lupine, western yarrow, prairie smoke and ballhead sandwort. There may still be remnant amounts of some of the late-seral species such as bluebunch wheatgrass and green/Columbia needlegrass present. The taller grasses will occur only occasionally, often within horizontal juniper plants. Palatable forbs will be mostly absent. Shrubby cinquefoil can become a significant component, particularly in the higher moisture areas (> 17 inches precipitation) of this MLRA/RRU. This plant community is the result of long-term, heavy, continuous grazing and/or annual, early spring seasonal grazing. 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. This community will respond positively to improved grazing management, but significant economic inputs and a signinicant amount of time are usually required to move this plant community toward a higher successional stage and a more productive plant community.
State 5
Mid and Short Grasses, Sedges, Non-Native Grasses
Community 5.1
Mid and Short Grasses, Sedges, Non-Native Grasses
As heavy disturbance continues, plant community 3 deteriorates to one similar to community number 4, except that non-native bluegrasses (Kentucky/Canada) and/or common timothy become more abundant, often comprising up to about 25 percent of the composition. These last 2 plant communities (4 & 5) are often less productive than Plant Communities 1, 2, or 3. 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. Plant Communities 4 and 5 have a high percentage of aggressive, less-desirable species, including Kentucky or Canada bluegrass or timothy. 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. Rest, usually for a number of years, can sometimes help with re-establishment of the desired species, depending on the amount of desirable species remaining. There are limitations to using seeding and/or mechanical treatment on this site due to the abundance of stones on these soils.
State 6
Weedy Forbs, Sageworts, Short Grasses, Creeping Juniper
Community 6.1
Weedy Forbs, Sageworts, Short Grasses, Creeping Juniper
If community 4 deteriorates further due to non-prescribed grazing or other disturbance, it becomes dominated by weedy forbs (pussytoes, cudweed sagewort, western yarrow, prairie smoke, field chickweed, northern bedstraw and ballhead sandwort), short grasses (Sandberg bluegrass, and prairie junegrass), and half shrubs such as fringed sagewort. There is often a remnant amount of some of the mid-seral grasses such as thickspike wheatgrass and Idaho fescue, usually widely spaced. Creeping juniper can become abundant in the northern part of this MLRU. Frequently, a remnant population of climax species such as bluebunch wheatgrass, tall needlegrasses, and rough fescue will occur within the creeping juniper.
State 7
Non-Native Grasses, Weedy Forbs, Clubmoss
Community 7.1
Non-Native Grasses, Weedy Forbs, Clubmoss
Further deterioration of community 5 due to non-prescribed grazing or other disturbance leads to a plant community dominated by Kentucky/Canada bluegrass and/or common timothy, often comprising up to 80 % of the community. Weedy forbs including field chickweed, cudweed sagewort, and pussytoes are abundant and typically comprise the rest of the plant composition. A thick cover of dense clubmoss often completes this community. Occasionally, in places receiving 17 inches or greater precipitation, some short lived native species such as mountain brome can become dominant after major disturbance from grazing or rodent (pocket gopher mainly) activity. Plant communities 6 and 7 produce less usable forage for wildlife and livestock 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. A thick canopy cover of creeping juniper often results in precipitation being intercepted, thus not reaching the soil. Most of the attributes of a healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling and energy flow, have been lost. These communities can respond positively to improved grazing management. Significant economic inputs are needed, along with extended rest and prescribed grazing management, to restore them to a higher successional stage. However, because of the stoniness 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 | 0–95 | ||||
Shrub, broadleaf | 2SB | Shrub, broadleaf | 0–35 | – | ||
prairie sagewort | ARFR4 | Artemisia frigida | 0–35 | – | ||
Grass/Grasslike
|
||||||
2 | Grasses and Grasslikes | 975–1490 | ||||
bluebunch wheatgrass | PSSP6 | Pseudoroegneria spicata | 490–1115 | – | ||
rough fescue | FECA4 | Festuca campestris | 490–1115 | – | ||
Idaho fescue | FEID | Festuca idahoensis | 120–280 | – | ||
porcupinegrass | HESP11 | Hesperostipa spartea | 0–185 | – | ||
prairie Junegrass | KOMA | Koeleria macrantha | 61–95 | – | ||
western wheatgrass | PASM | Pascopyrum smithii | 0–95 | – | ||
Cusick's bluegrass | POCU3 | Poa cusickii | 0–95 | – | ||
Sandberg bluegrass | POSE | Poa secunda | 61–95 | – | ||
needle and thread | HECOC8 | Hesperostipa comata ssp. comata | 0–95 | – | ||
big quakinggrass | BRMA | Briza maxima | 0–95 | – | ||
needleleaf sedge | CADU6 | Carex duriuscula | 61–95 | – | ||
threadleaf sedge | CAFI | Carex filifolia | 61–95 | – | ||
sun sedge | CAINH2 | Carex inops ssp. heliophila | 61–95 | – | ||
plains reedgrass | CAMO | Calamagrostis montanensis | 61–95 | – | ||
Parry's oatgrass | DAPA2 | Danthonia parryi | 0–95 | – | ||
tufted wheatgrass | ELMA7 | Elymus macrourus | 0–95 | – | ||
Columbia needlegrass | ACNEN2 | Achnatherum nelsonii ssp. nelsonii | 30–93 | – | ||
green needlegrass | NAVI4 | Nassella viridula | 30–93 | – | ||
Grass, perennial | 2GP | Grass, perennial | 0–61 | – | ||
purple threeawn | ARPU9 | Aristida purpurea | 0–1 | – | ||
Fendler's threeawn | ARPUF | Aristida purpurea var. fendleriana | 0–1 | – | ||
Forb
|
||||||
3 | Forbs | 0–370 | ||||
leafy wildparsley | MUDI | Musineon divaricatum | 0–95 | – | ||
beardtongue | PENST | Penstemon | 0–95 | – | ||
spiny phlox | PHHO | Phlox hoodii | 0–95 | – | ||
scurfpea | PSORA2 | Psoralidium | 0–95 | – | ||
cutleaf anemone | PUPAM | Pulsatilla patens ssp. multifida | 0–95 | – | ||
prairie thermopsis | THRH | Thermopsis rhombifolia | 0–95 | – | ||
American vetch | VIAM | Vicia americana | 0–95 | – | ||
Forb, perennial | 2FP | Forb, perennial | 0–95 | – | ||
common yarrow | ACMI2 | Achillea millefolium | 0–95 | – | ||
pale agoseris | AGGL | Agoseris glauca | 12–95 | – | ||
onion | ALLIU | Allium | 0–95 | – | ||
pussytoes | ANTEN | Antennaria | 0–95 | – | ||
aster | ASTER | Aster | 0–95 | – | ||
milkvetch | ASTRA | Astragalus | 0–95 | – | ||
balsamroot | BALSA | Balsamorhiza | 0–95 | – | ||
Bonneville shootingstar | DOCO | Dodecatheon conjugens | 12–95 | – | ||
erigenia | ERIGE | Erigenia | 0–95 | – | ||
yellow fritillary | FRPU2 | Fritillaria pudica | 0–95 | – | ||
Richardson's geranium | GERI | Geranium richardsonii | 12–95 | – | ||
old man's whiskers | GETR | Geum triflorum | 0–95 | – | ||
sticky purple geranium | GEVI2 | Geranium viscosissimum | 12–95 | – | ||
western stoneseed | LIRU4 | Lithospermum ruderale | 0–95 | – | ||
desertparsley | LOMAT | Lomatium | 0–95 | – | ||
lupine | LUPIN | Lupinus | 0–1 | – | ||
larkspur | DELPH | Delphinium | 0–1 | – | ||
deathcamas | ZIGAD | Zigadenus | 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.
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 through 7, 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 or 3 (medium and short grasses) occur, grazing management strategies that will prevent further degradation need to be implemented. These communities are still stable, productive, and healthy provided they receive proper management. They will respond fairly quickly to improved grazing management, including increased growing season rest of key forage plants. Grazing management alone can usually move these back towards the potential / historic climax community.
Plant communities 4 through 7 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. These communities can occur throughout the pasture, on spot grazed areas, and around water sources where season-long grazing patterns occur.
It becomes critical at this point to implement a grazing strategy that will restore the stability and health of the site. Rest, usually for a number of years, can sometimes help with re-establishment of the desired species, depending on the amount of desirable species remaining.
Communities 6 and 7 have a high percentage of aggressive, less-desirable species and have lost most of the attributes of a healthy rangeland, including good infiltration, minimal erosion and runoff, nutrient cycling and energy use. Once this site is occupied by these communities it will be more difficult to restore it to a community that resembles the potential with grazing management alone. Additional growing season rest combined with accelerated practices (e.g. range seeding, chiseling) are often necessary for re-establishment of the desired species and to restore the stability and health of the site. However, there are limitations to using seeding and/or mechanical treatment on this site due to the stony 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 soils associated with this ecological site are generally in Hydrologic Soil Group B. The infiltration rates for these soils will normally be moderate. The runoff potential for this site is moderate, depending on slope and ground cover/health. Runoff curve numbers generally range from 64 to 82.
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 1 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 3, 4 and 5) are generally considered to be in poor hydrologic condition as a majority of the plant cover is from shallow-rooted species such as blue grama and annual grasses.
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; Loretta Metz; Peter Husby
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) | J. Siddoway, R. Bandy, G. Petersen |
---|---|
Contact for lead author | grant.petersen@usda.gov |
Date | 04/19/2005 |
Approved by | Kirt Walstad |
Approval date | |
Composition (Indicators 10 and 12) based on | Annual Production |
Indicators
-
Number and extent of rills:
Slopes most common on this site are between 0 – 8% and with at least 95% of the soil surface covered there are rills would be uncommon unless after the most extreme convection storms. Rills could be more common on slopes of 9 – 15% with moderate to severe convection storms. -
Presence of water flow patterns:
Due to the soil surface being well covered and minimal slope there is no evidence of past or current soil deposition or erosion for this site. -
Number and height of erosional pedestals or terracettes:
Wind and water erosion will not be evident on this site, so pedestals and terracettes will not be present. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground should be no more than 5% on this site. -
Number of gullies and erosion associated with gullies:
Gully erosion will not be evident on this site. -
Extent of wind scoured, blowouts and/or depositional areas:
Appearance or evidence of these erosional features on the landscape would not be present on this site. -
Amount of litter movement (describe size and distance expected to travel):
Because there is little bare ground, litter movement will be minimal at most. Because the site is dominated by the taller bunchgrasses, litter size will reflect the height and diameter of the reproductive culms and leaves of these grasses as well as the lesser dominate mid-size grasses. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Resistance to erosion will be high with soil stability values of 5 or 6; areas of bare soil on this site may have values less than 5 if not under plant canopy. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Soil surface structure is granular; A horizon depth is 5 – 11”. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Dominance of taller, deep rooted bunchgrasses will maximize infiltration and minimize runoff throughout the site. -
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
Will not be present generally, but there may be areas that have “healed” from former bison trails and wallows as well as more current livestock trails which could have a compaction layer below the soil surface. -
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:
Cool season, taller bunchgrasses (rough fescue, bluebunch wheatgrass)Sub-dominant:
perennial forbs > cool season midgrasses (Idaho fescue) > cool season rhizomatous grasses (thickspike wheatgrass) > warm season, short bunchgrass (plains muhly) = sedges > shrubsOther:
Additional:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Will be low for all functional groups in a given year. Prolonged droughts which last more than 3 years may show increases in mortality and decadence for all plant groups. -
Average percent litter cover (%) and depth ( in):
Variable litter cover that tends to be thin. -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
1200 - 1900 #/acre. This would be the expected production for the reference state during adequate moisture years. 1700 pounds would be the expected production in a 17 inch precipitation zone. -
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:
Kentucky/Canada bluegrass, shrubby cinquefoil, dense clubmoss, Japanese brome, a variety of annual or biennial weedy forbs, fringed and cudweed sagewort, broom snakeweed, pussytoes, creeping juniper, field chickweed, ballhead sandwort, western yarrow, cheatgrass. -
Perennial plant reproductive capability:
During adequate moisture years bunchgrasses will generally produce seeds, however the cool season rhizomatous grasses may not necessarily produce seed even with adequate moisture.
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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.
Click on box and path labels to scroll to the respective text.