Physiographic features

This ecological site occurs on nearly level to strongly sloping sedimentary plains, terraces, and fans. It often has a dune like topography. The slopes are 0-15%, but mainly are less than 8%. This site occurs on all exposures. Aspect is not significant.

Table 2. Representative physiographic features

Climatic features

MLRAs 58A and 60B are considered to have a continental climate characterized by cold winters, hot summers, low humidity, light rainfall, and much sunshine. Extremes in temperature are typical. The climate is the result of this MLRA’s location in the geographic center of North America. There are few natural barriers on the northern Great Plains and the winds move freely across the plains and account for rapid changes in temperature. Seasonal precipitation is often limiting for plant growth. Annual fluctuations in species composition and total production are typical depending on the amount and timing of rainfall.
Temperatures can be very extreme in this part of Montana. Summer daytime temperatures are typically quite warm, generally averaging in the mid to upper 80º’s F for July and August. Summertime temperatures will typically reach in the 100º’s F at some point during the summer, and can reach 90º F any month between May and September. Conversely, winter temperatures can be cold, averaging in the mid teens to mid 20º’s F for December and January. There will typically be several days of below zero temperatures each winter. It is not uncommon for temperatures to reach 30–40º F below zero, or even colder, most any winter.

Spring can be windy throughout these MLRA’s, with winds averaging over 10 mph about 15 percent of the time. Speeds of 50 mph or stronger can occasionally occur as a weather system crosses this part of Montana.

MLRAs 58AE and 60BE have been divided into two distinct precipitation zones for the purpose of developing ecological site descriptions: 10–14” Mean Annual Precipitation (MAP) and 15–19” MAP.


10–14 inch zone:

The majority of the rangeland in these areas falls within the 11 to 13 inch range. During an average year, 70 to 75 percent of the annual precipitation falls between April and September, which are the primary growing season months.

Snowfall is not heavy in the area, averaging 28 total inches in the 10-14 inch MAP (Yellowstone Valley). Heavy snowfall occurs infrequently, usually late in the winter or early spring. Snow cover is typically 1 to 3 inches.

The frost free (32º F.) season averages about 105 to 145 days each year in the uplands, to nearly 170 days along the Yellowstone River Valley.

For local climate station information, refer to http://www.wcc.nrcs.usda.gov/cgibin/state.pl?state=mt.

Table 3. Representative climatic features

Influencing water features

Soil features

The soils are sands and loamy sands more than 20 inches deep. These soils are very susceptible to wind erosion.

Table 4. Representative soil features

Animal community

Livestock Grazing Interpretations:

Managed livestock grazing is suitable on this site as it has the potential to produce an abundance of high quality forage. The abundance of warm season species makes
this site especially valuable for use during mid-summer when the cool season species are past their optimum period of quality forage.

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.

Whenever Plant Community 2 occurs (medium and short grasses), grazing management strategies need to be implemented to avoid further deterioration. This community is still stable, productive, and healthy provided it receives proper management. This community will respond fairly quickly to improved grazing management including increased growing season rest of key forage plants. Grazing management alone can usually move this community back to one more similar to potential.

Plant Communities 3 or 4 have extremely limited forage production (< 600 pounds per acre), and a high percentage of non-preferred species for cattle and sheep. 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 is often necessary for re-establishment of the desired species and to restore the stability and health of the site. Seeding may be necessary to restore desirable native perennial species.

Wildlife Interpretations:

The following is a description of habitat values for the different plant communities that may occupy the site:

Plant Community 1: Tall and Medium Grasses/Forbs/Shrubs (HCPC):
The predominance of grasses and sedges plus a diversity of forbs and half-shrubs in this community favors grazers and mixed feeders such as bison, pronghorn and elk. An abundance of warm season grasses extends the availability of nutritious forage throughout the summer. Suitable escape cover for mule deer is limited because of low shrub cover unless topographic features provide this habitat. The mix of tall and medium height grass residual cover along with abundant litter production creates favorable habitat for ground nesting birds including sharp-tailed grouse, upland sandpipers, vesper sparrows and grasshopper sparrows. Raptors are attracted to the diverse prey populations. A variety of forbs, grasses and half-shrubs attracts seed–eating small mammals like deer mice and pocket mice while heavy litter production favors herbivorous voles.

Plant Community 2: Medium and Short Grasses/ Medium Shrubs:
A reduction of warm-season grasses shortens the green feed period for grazers. Habitat value for ground-nesting birds and herbivorous small mammals is reduced as litter and residual grass production declines. Reduction of vegetative structural complexity decreases general habitat value for a variety of wildlife species.

Plant Community 3: Shrubs/ Medium and Short Grasses/ Half-shrubs:
Habitat value is poor for most wildlife species. Further reduction of litter and residual grass production limits ground-nesting bird habitat, although species favoring sparse cover, including long-billed curlews, McCown’s longspur and horned larks may nest in this community. Annual grass and forb production may support populations of deer mice.

Plant Community 4: Shrubs and Half-shrubs/ Short Grasses/ Cacti:
Unstable dunes provide poor habitat values for the majority of wildlife species. After stabilization by tall and medium warm and cool season grasses, habitat values may be similar to Plant Community 1, above.

Hydrological functions

The soils associated with this ecological site are generally in Hydrologic Soil Group A. The infiltration rates for these soils will normally be rapid to very rapid. The runoff potential for this site is very low. Runoff curve numbers generally range from 47 to 77.

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 1and 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 and 4) are generally considered to be in poor hydrologic condition as the majority of plant cover is from shallow-rooted annuals 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 recreational opportunities for big game and upland bird hunting, and hiking. The forbs have flowers that appeal to photographers. This site provides valuable open space and visual aesthetics. Travel across this site can be difficult because of the loose sand.

Other information

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 AUM/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).

Inventory data references

NRCS-Production & Composition Record for Native Grazing Lands (Range-417): 6

BLM-Soil & Vegetation Inventory Method (SVIM) Data: 10

NRCS-Range Condition Record (ECS-2): 8

NRCS-Range/Soil Correlation Observations & Soil 232 notes: 11

Contributors

Bob Leinard
JVF, REL, RSN, MJR, SKW, SVF, POH