Physiographic features

The Loamy Platte valley (Ly) ecological site (R034AI122WY) is located within LRU “I” in MLRA “34A.” This ecological site occurs in intermontane basin landscapes on hill, draw, pediment, and fan remnant landforms (see definitions below). The slope ranges from level to 15%. This site occurs on all aspects.
fan remnant – A general term for landforms that are the remaining parts of older fan-landforms, such as alluvial fans, fan aprons, inset fans, and fan skirts, that either have been dissected (erosional fan-remnants) or partially buried (nonburied fan-remnants). An erosional fan remnant must have a relatively flat summit that is a relict fan-surface.
intermontane basin – A generic term for wide structural depressions between mountain ranges that are partly filled with alluvium and called "valleys" in the vernacular.
hills – A landscape dominated by hills and associated valleys. The landform term is singular (hill).

Table 2. Representative physiographic features

Climatic features

Annual precipitation ranges from 9-12 inches per year. Wide fluctuations may occur in yearly precipitation and result in more dry years than those with more than normal precipitation. Temperatures show a wide range between summer and winter and between daily maximums and minimums. This is predominantly due to the high elevation and dry air, which permits rapid incoming and outgoing radiation. Cold air outbreaks in winter move rapidly from northwest to southeast and account for extreme minimum temperatures.

Much of the precipitation accumulation (45%) comes in the spring/summer(April to August). The wettest month is May (1.22 inches). The growing season is short (90-120 days average) and cool: primary growth typically occurs between May and June. The dominant plants (sagebrush and cool season grasses) are well adapted to these conditions.
Daytime winds are generally stronger than nighttime and occasional strong storms may bring brief periods of high winds with gusts to more than 50 mph.

Growth of native cool season plants begins about mid-April and continues to approximately early-July. Some green up of cool season plants usually occurs in September with adequate fall moisture.

Table 3. Representative climatic features

Climate stations used

• (1) SARATOGA [USC00487990], Saratoga, WY

• (2) RAWLINS MUNI AP [USW00024057], Rawlins, WY

Influencing water features

None

Soil features

The soils of this site are moderately deep to very deep(greater than 20" to bedrock), and well-drained. Textures range from loams to very fine sandy loam on the coarse end to light clay loam (<30% clay content) on the heavy end. The most common textures include loam, silt loam, and sandy clay loam. A highly common scenario is to have a 1 to 3” cap of sandy loam over a sandy clay loam due to young soil development of weathered sandstone and shale parent materials.

Table 4. Representative soil features

Animal community

The following table lists suggested stocking rates for cattle under continuous season-long grazing under normal growing conditions. These are conservative estimates that should be used only as guidelines in the initial stages of the conservation planning process. Often, the current plant composition does not entirely match any particular plant community (as described in this ecological site description). Because of this, a field visit is recommended, in all cases, to document plant composition and production. More precise carrying capacity estimates should eventually be calculated using this information along with animal preference data, particularly when grazers other than cattle are involved. Under more intensive grazing management, improved harvest efficiencies can result in an increased carrying capacity, but recovery time for upland sites is much longer than in a low intensity system. If distribution problems occur, stocking rates must be reduced or facilitating conservation practices (i.e. cross-fencing, water development) to maintain plant health and vigor.


Plant Community Production Carrying Capacity*
(lb./ac) (AUM/AC) (AC/AUM)
Big Sagebrush/Bunchgrass (Reference) 500-700-900 (.10) (10)
Bunchgrass/Big Sage 500-700-900 (.12) (8)
Bunchgrass 500-700-900 (.13) (8)
Big Sage/Rhizomatous Wheatgrass 200-400-650 (.05) (20)
Big Sage/Bare Ground 100-300-500 (.03) (33.3)
Rabbitbrush/Bare Ground 100-300-500 (.03) (33.3)
Big Sage/Rabbitbrush 100-300-500 (.03) (33.3)
* - Continuous, season-long grazing by cattle under average growing conditions.

**Calculation for stocking rates are as follows: using RV values for production, take forage palatable to grazing cattle multiply by 0.25 harvest efficiency and divide by 912.5 (air dried weight) to arrive at carrying capacity.

Grazing by domestic livestock is one of the major income-producing industries in the area. Rangeland in this area may provide yearlong forage for cattle, sheep, or horses. During the dormant period, the forage for livestock use needs to be supplemented with protein because the quality does not meet minimum livestock requirements.

Distance to water, shrub density, and slope can affect grazing capacity within a management unit. Adjustments should be made for the area that is considered necessary for reduction of animal numbers. For example, 30% of a management unit may have 25% slopes and distances of greater than 1 mile from water; therefore the adjustment is only calculated for 30% of the unit (i.e. 50% reduction on 30% of the management unit). Fencing, slope length, management, access, terrain, kind and class of livestock, and breeds are all factors that can increase or decrease the percent of graze-able acres within a management unit. Adjustments should be made that incorporate these factors when calculating stocking rates.

Wildlife Community

The Loamy (Ly) ecological site in 34A Cool Central Desertic Basins and Plateaus, LRU I (Platte Valley) provides suitable and valuable habitat for a variety of wildlife species. In most cases, the greater the density and diversity in grass, forb, and shrub species within the site, the greater the diversity of wildlife the site can support including insects which many wildlife species depend on for their dietary requirements.
Mid-sized cool season bunchgrasses provide forage and cover for big game species, small mammals, birds, and reptiles. Wildlife such as elk, cottontails, jackrabbits, and prairie dogs depend largely on grass for forage. Birds nest among the bunchgrasses and utilize the grass as screening cover from predatory wildlife. Mule deer, pronghorn, greater sage-grouse, and songbirds utilize the taller grasses amongst the shrubs as hiding cover for their young.
Sagebrush, which can approach 15% protein and 40­-60% digestibility, provides important winter forage
for greater sage­grouse, mule deer, and pronghorn. Year­round habitat is provided for sage-grouse
and other sagebrush obligate species such as cottontails, pygmy rabbit, sagebrush vole, short­horned lizard, and pronghorn. Seasonal habitat needs are provided for migrants such as sage sparrow,
Brewer’s sparrow, and sage thrasher and other sagebrush obligate songbirds.. Other birds that
frequent this plant community include horned larks and golden eagles.

Forbs are an important component of this habitat type, providing an early food source for sage-grouse chicks both nutritionally and via the insects that forbs attract. Forbs provide necessary moisture to wildlife in arid landscapes. Mule deer and pronghorn are dependent on abundant forbs to aid in the production of milk to nurse fawns and as forage for fawn development and health.

Reference State:

1.1 Big Sagebrush/Bunchgrass: This plant community provides optimal winter habitat for sage-
grouse, mule deer, pronghorn, and other species that depend on shrubs that stand up through the snow
for forage. These areas also provide high quality bird nesting habitat where sagebrush canopy and residual bunchgrasses hide nests and young from predators. Forbs are necessary in the understory
of this plant community to attract insects that are a highly nutritious spring food source for
sage-grouse chicks and other sagebrush obligate bird species.

1.2 Bunchgrass/WY Big Sagebrush: This vegetation community tends to have higher herbaceous plant
diversity that may attract more diverse wildlife use. The state provides suitable forage and cover for sagebrush obligate species. The more open canopy promotes higher diversity and quantity of forbs that are important for early sage-grouse brood­rearing habitat. A reduced sagebrush canopy may result in a slightly lower nesting frequency by sage­grouse and songbirds. Winter use by mule deer and pronghorn may be significant and some shrubs may become hedged over time with excessive browsing. Yearlong elk use in these areas can be high due to the abundance of bunchgrass.

1.3 Bunchgrass Community: This plant community provides foraging habitat for sage­grouse when in
proximity to areas with denser sagebrush cover. Due to the higher production of perennial cool-
season grasses, this vegetation type provides high forage value for wintering elk. Mule deer and
pronghorn may transition through these habitats during their annual migrations between summer and
winter ranges. It also provides suitable habitat for burrowing animals.

Grazing Resistant State:

2.1 Big Sagebrush/Rhizomatous Wheatgrass­Sandberg Bluegrass­Mat Forb: This plant
community is variable in its value to wildlife. The value of the sagebrush community is similar to the reference state but the value of the grass community decreases. In periods of high plant vigor, the grass plants can provide cover for nesting birds and small mammals. In periods of drought and low plant vigor and diversity, especially low forb availability, grass plants are too short and not dense enough to provide adequate cover and the wildlife value of these areas declines. Mat-forming forbs often occupy the space and nutrients needed for more desirable forbs such as globemallow, bitterroot, and yarrow.

Eroded State:

3.1 Big Sagebrush/Bare Ground: This plant community provides suitable winter habitat for
foraging big game and sage­grouse when sagebrush is in a healthy state and stands above winter snows. The lack of herbaceous species limits the value of the site for birds and small mammals due to the lack of cover in the interspaces of the sagebrush plants. The lack of plant diversity limits the diversity of insects used by wildlife species.

Disturbed State:

4.1 Rabbitbrush/Bare Ground/Annuals: This plant community is capable of producing a high number of insects which are important for pollination and bird forage. In some areas, rabbitbrush is used heavily by wintering mule deer, especially when other preferred winter forages are unavailable or in poor vigor due to over-use or drought. Annual plants have little nutritive value and are typically too short to provide hiding cover for wildlife. Big game animals may garner some early spring or fall benefit from newly sprouted annual forage, but the timing is short where wildlife can benefit, especially from cheatgrass sprouts. Chukars are a species that utilizes cheatgrass seed as a food source, and they may benefit from areas of cheatgrass invasion. This state is vulnerable to repeated wildfire which can result in a complete loss of value for wildlife. Bare ground provides essentially no habitat value for wildlife. In addition, bare ground may be more susceptible to invasion of non-native species, further degrading the value for wildlife.

4.2 Big Sagebrush/Rabbitbrush: The value of the big sagebrush in this state is similar as described in the previous states. Depending on the sub­species of rabbitbrush found in this plant community it can provide forage value in transitional and winter ranges for big game species. Sage-grouse and
other birds may forage within this plant community where insect quantity and diversity is high. The
lack of an herbaceous community limits the value as bird and small mammal hiding cover and forage for grazing animals.

Highly Disturbed State:
5.1 Annuals/Bare Ground: As described in the Rabbitbrush/Bare Ground/Annuals state above, annuals and bare ground hold little value for wildlife due to the lack of suitable forage and cover. This state is vulnerable to an increase in weedy species that can migrate into adjacent areas, degrading the adjacent areas’ value for wildlife.

5.2 Reclaimed: How the site was reclaimed, the species planted, and the time it takes for plants to establish will determine the value of the site for wildlife. A fully reclaimed site containing a diversity of herbaceous and woody plants should provide the same wildlife habitat benefits as the reference state. In most cases, grasses and forbs establish early in the reclamation process, whereas shrubs take significantly longer to establish. Wildlife species dependent on a herbaceous plant community for forage and cover (elk, prairie dogs, chukars, and swift fox) will benefit from reclamation sooner than those species dependent on a shrub/grass community. Suitable habitat for wildlife species which require tall, dense sagebrush (greater sage-grouse, pronghorn, mule deer, and sagebrush obligate songbirds) will likely not benefit from reclamation for a decade or longer, providing shrub species were planted and/or seed from shrubs adjacent to the area have established on-site.

Hydrological functions

Water is the principal factor limiting forage production on this site. This site is dominated by soils in hydrologic group B (infiltration rate of 0.15-0.3 in/hr), with localized areas in hydrologic groups A (infiltration rate of 0.3 in/hr) and C (infiltration rate of 0.05-0.15 in/hr). Infiltration ranges from rapid to moderate. Runoff potential for this site varies from low to moderate depending on soil hydrologic group and ground cover. In many cases, areas with greater than 75% ground cover have the greatest potential for high infiltration and lower runoff. Areas where ground cover is less than 50% have the greatest potential to have reduced infiltration and higher runoff (refer to Part 630, NRCS National Engineering Handbook for detailed hydrology information).

Rills and gullies should not typically be present. Water flow patterns should be barely distinguishable if at all present. Pedestals are only slightly present in association with bunchgrasses and shrubs. Litter typically falls in place, and signs of movement are not common. Chemical and physical crusts are rare to non-existent. Cryptogrammic crusts are present, but only cover 1-2% of the soil surface.

Recreational uses

This site provides some limited recreational opportunities for hiking, horseback riding, bird watching, and upland game hunting. The forbs have a variety of colors and shapes that appeal to photographers. This site provides valuable open space when located in large, unfragmented landscapes

Wood products

NONE

Other products

NONE

Other references

Bestelmeyer, B., & Brown, J. (2005). State-and-transition models 101: a fresh look at vegetation change. The Ouivira Coalition Newsletter, Vol. 7, No. 3.
Bestelmeyer, B., Brown, J., Havstad, K., Alexander, B., Chavez, G., & Herrick, J. (2003). Development and use of state and transition models for rangeland. Journal of Range Management, 56(2): 114-126.
Bestelmeyer, B., Herrick, J., Brown, J., Trujillo, D., & Havstad, K. (2004). Land management in the American Southwest: a state-and-transition approach to ecosystem complexity. Environmental Management, 34(1): 38-51.
Carney, J., Bainter, E., Budd, B., Christiansen, T., Herren, V., Holloran, M., et al. (2010). Grazing Influence, Objective Development, and Mangement in Wyoming's Greater Sage-Grouse Habitat. Unpublished, 36.
Derner, J. D., Schuman, G. E., Follett, R. F., & Vance, G. F. (2014). Plant and Soil Consequences of Shrub Management in a Big Sagebrush-Dominated Rangeland Ecosystem. Environment and Natural Resources Research, 19-30.
Natural Resouces Conservation Service. (n.d.). USDA Plants Database. Retrieved from http://plants.usda.gov/java/
Sommers, J. (1994). Green River Drift- A History of the Upper Green River Cattle Association. ISBN: 1-56044-280-8.
Stiver, S., Rinkes, E., & Naugle, D. (2010). Sage-Grouse Habitat Assessment Framework. Unpublished, 100-106.
Stringham, T., Kreuger, W., & Shaver, P. (2003). State and transition modeling: an ecological process approach. Journal of Range Management, 56(2): 106-113.
Winward, A. (2007). Boulder, Squaretop Area Field Notes. Unpublished.

Approval

Kirt Walstad, 9/28/2023