Physiographic features

The Gravelly Pinedale Plateau (Gr-PP) ecological site occurs in intermontane basin landscapes on hillslope, mesa, and escarpment landforms (see following definitions). It is typically found on summit and shoulder positions and on all exposures. Slopes are typically from 15 to 45 percent, but can occur on any slope, and at elevations mostly above 7000 feet.

Landscape:
intermontane basin - A generic term for wide structural depressions between mountain ranges that are partly filled with alluvium and called "valleys" in the vernacular. Intermontane basins may be drained internally (bolsons) or externally (semi-bolson).

Landform:
escarpment - A relatively continuous and steep slope or cliff produced by erosion or faulting and that topographically interrupts or breaks the general continuity of more gently sloping land surfaces . The term is most commonly applied to cliffs produced by differential erosion.

hill - A generic term for the steeper part of a hill between its summit and the drainage line, valley flat, or depression floor at the base of the hill.

mesa - An isolated, flat-topped, landform that stands distinctly above the adjacent land area and is bounded by steep slopes or cliffs; and is generally capped by erosion-resistant, nearly horizontal rock (often lava). Mesas and buttes have similar forms and isolated occurrence. A mesa has a summit area broader than the bounding cliff height. Mesas are most common in arid and semi-arid regions, but are not climatically restricted.

summit - (a) The topographically highest position of a hillslope profile with a nearly level (planar or only slightly convex) surface. Compare - shoulder, backslope, footslope, and toeslope, crest. (b) A general term for the top, or highest area of a landform such as a hill, mountain, or tableland. It usually refers to a high interfluve area of relatively gentle slope that is flanked by steeper slopes, e.g., mountain fronts or tableland escarpments.

shoulder - The hillslope profile position that forms the convex, erosional surface near the top of a hillslope. If present, it comprises the transition zone from summit to backslope. Compare - summit, crest, backslope, footslope, and toeslope.

Table 2. Representative physiographic features

Climatic features

Annual precipitation ranges from 9 to 12 inches per year. Wide fluctuations may occur in yearly precipitation and result in more below average years than those with above average 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 percent) comes in the winter in the form of snow (October to April). The wettest month is May (1.69 inches). 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 miles per hour. The growing season is short (less than 60 day) and cool (critical growth period): primary growth typically occurs between May and June.
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.

All data is based on the 30-year average from 1981-2010.

Table 3. Representative climatic features

Climate stations used

• (1) PINEDALE [USC00487260], Pinedale, WY

• (2) CORA [USC00482054], Cora, WY

• (3) BOULDER REARING STN [USC00480951], Boulder, WY

Influencing water features

There are no influencing water features in the Gravelly Pinedale Plateau ecological site.

Wetland description

N/A

Soil features

The soils of this site are moderately deep to deep, well-drained soils formed in colluvium and slope alluvium. These soils are usually sandy loam to loam. This site usually occurs on steep slopes, but may be on any slope. Surface modifiers are typically very gravelly or very cobbly (rounded) with the volume either maintained or decreasing throughout the soil profile. A common scenario is a cobbly surface cap with less rock fragments in the subsoil.

Major Soil Series correlated to this site include: Foursees and Roto
Representative soil taxonomy: Loamy-skeletal, carbonatic, frigid Aridic Calciustepts or
Loamy-skeletal, mixed, superactive, frigid Aridic Calciustepts

Table 4. Representative soil features

Animal community

Livestock:
The following table lists suggested stocking rates for cattle under continuous season-long grazing under normal growing conditions with a harvest efficiency (HE) of 25 percent. 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). A field visit is required to document actual plant composition and production. More precise carrying capacity estimates, considering forage preference and accessibility (slope, distance to water, etc.), should be calculated using field data, particularly when grazers other than cattle are involved. Under more intensive grazing management, improved harvest efficiencies (up to 35 percent) can result in an increased carrying capacity, but recovery time for upland sites is much longer. If distribution problems occur, stocking rates should be reduced or facilitating conservation practices (i.e., cross-fencing, water development) implemented to maintain plant health and vigor.

Stocking rates are expressed in Animal Unit Months (AUMs) which is defined as the amount of forage consumed by a 1,000 lb. cow with a less than 4 month old calf at her side.

Initial Suggested Stocking Rate:
Plant Community Production (lbs./ac.) (AUMs/ac.)* Ac./AUM
1.1 Bunchgrass 300-450-550 0.08 13
2.1 Short-stature Grass/Mat-forming Forb 150-300-450 0.05 20
3.1 Reclaimed 300-450-550 0.1 10
3.2 Annual 100-200-300 0.02 50

* 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 and multiply by 0.25 HE and divide by 912.5 pounds per AUM air-dry weight (ADW) to arrive at the initial suggested stocking rate in AUMs per acre.

Grazing by domestic livestock is one of the major income-producing industries in the area. Rangeland in this area may provide year-long forage, but is typically used in the spring. During the dormant period, the forage for livestock must 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. Accessibility adjustments should be made for the planning area as necessary. For example, 30 percent of a management unit may have 25 percent slopes and distances of greater than one mile from water, resulting in a 50 percent reduction in grazing access; therefore, the adjustment is calculated for 30 percent of the unit (i.e. 50 percent reduction on 30 percent 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 grazing access within a management unit. Adjustments should be made that incorporate these factors when calculating the carrying capacity of a management unit.

Wildlife:
Reference State
1.1 Bunchgrass Community: This community phase provides great habitat for elk, pronghorn, mule deer, and sage grouse throughout various times of the year. Value is lower for species dependent on shrubs, however, during winter months these sites are prone to being windblown allowing better access to forage especially for big game species. In addition, given the diverse suite of herbaceous species, this phase also provides important micronutrient requirements for big game species throughout the year as well as during the spring green up for migrating animals. Numerous small mammals and songbirds benefit from this state as well, providing foraging opportunities near nesting and cover habitats.

Grazing Resistant State
2.1 Short-stature Grass/Mat-forming Forb Plant Community: This community phase is variable in its value to wildlife. Value is low for species dependent on shrubs similar to the reference state, unless in close proximity to areas with a more dominant shrub community. This phase still provides winter forage access similar to the reference state, however, with a reduction in grass species, especially the mid-size cool season bunchgrasses, the value to wildlife has been reduced.

Highly Disturbed State
3.1 Reclaimed Plant Community: This community phase is highly variable in its value to wildlife. Reclamation success, size and configuration of the reclaimed area, 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 native plants can eventually 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 herbaceous plant communities for forage (such as elk) will benefit from reclamation sooner than those species dependent on communities with a shrub component.
3.2 Annual Plant Community: This plant community exhibits a low level of plant species diversity, and thus, is less apt to meet the seasonal needs of most wildlife who frequent this community. Small mammals and songbirds will still utilize this phase, although not to the capacity as the above states.

Hydrological functions

Water is the principal factor limiting forage production on this site. This site is highly variable and is dominated by soils in hydrologic groups B and C. Infiltration ranges from moderately slow to moderate. Runoff potential for this site varies from moderate to high depending on soil hydrologic group, slope and ground cover. In many cases, areas with greater than 75 percent ground cover have the greatest potential for high infiltration and lower runoff. An example of an exception would be where short-grasses form a strong sod and dominate the site. Areas where ground cover is less than 50 percent 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 are not typically present due to rock fragments on the surface that armor the site. Water flow patterns should be barely distinguishable. Pedestals are only slightly present in association with bunchgrasses . Litter typically falls in place, and signs of movement are not common. Chemical and physical crusts are rare to non-existent. Biological crusts are present, but only cover one to two percent of the soil surface.

Recreational uses

This site provides hunting opportunities for upland game species. The wide variety of plants which bloom in the spring have an aesthetic value that appeals to recreationists and combined with landscape position attract pollinators such as butterflies.

Wood products

No wood products are present on the site.

Inventory data references

Information was derived from 1988 Range Site Descriptions, NRCS clipping data, literature, field observations (based on two sampled sites and observations from numerous others), and personal contacts with range-trained personnel (i.e., agency specialists, landowners, land managers, and scientists).

References

• Bestelmeyer, B., J.R. Brown, K.M. Havstad, B. Alexander, G. Chavez, and J.E. Herrick. 2003. Development and Use of State and Transition Models for Rangelands. Jornal of Range Management 56:114–126.

• Bestelmeyer, B., J.R. Brown, J.E. Herrick, D.A. Trujillo, and K.M. Havstad. 2004. Land Management in the American Southwest: a state-and-transition approach to ecosystem complexity. Environmental Management 34:38–51.

• Bestelmeyer, B. and J. Brown. 2005. State-and-Transition Models 101: A Fresh look at vegetation change.

• Bowker, K.A. 2000. Jonah Field: A Shallow Sweetspot in the Basin-Centered Gas Accumulation of the Northern Green River Basin, Wyoming..

• Chambers, J.C., J.L. Beck, T.J. Christiansen, K.J. Clause, J.B. Dinkins, K.E. Doherty, K.A. Griffin, D.W. Havlina, K.F. Henke, L.L. Kurth, J.D. Maestas, M. Manning, K.E. Mayer, B.A. Mealor, C. McCarthy, M.A. Perea, and D.A. Pyke. 2016. Using resilience and resistance concepts to manage threats to sagebrush ecosystems, Gunnison sage-grouse, and Greater sage-grouse in their eastern range: A strategic multi-scale approach.. Gen. Tech. Rep. RMRS-GTR-356.. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fort Collins, CO. 1–143.

• Chambers, J.C., D.A. Pyke, J.D. Maestas, M. Pellant, C.S. Boyd, S.B. Campbell, S. Esipinosa, D.W. Havlina, K.E. Mayer, and A. Wuenschel. 2014. Using resistance and resilience concepts to reduce impacts of invasive annual grasses and altered fire regimes on the sagebrush ecosystem and greater sage-grouse: A strategic multi-scale approach.. Gen. Tech. Rep. RMRS-GTR-326.. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station., Fort Collins, CO. 73.

• Clause, K. and J. Randall. 2014. Wyoming Sagebrush Die-Off Report. Unpublished.

• Martin, J.L. 1996. Geohydrology of Tertiary Rocks in the Green River Structural Basin in Wyoming, Utah, and Colorado.. Water-Resources Investigations Report 92-4164. US Geological Survey.

• Miller, J.F., R.H. Frederick, and R.J. Tracey. 1973. “Precipitation-Frequency Atlas of the United States” NOAA Atlas 2, Volume 2 (Wyoming). National Weather Service, Silver Spring, Maryland.

• Stringham, T.K., W.C. Kreuger, and P.L. Shaver. 2003. State and Transition Modeling: an ecological process approach. Journal of Range Management 56:106–113.

• U. S. Environmental Protection Agency. 2010. Level III and IV ecoregions of the continental United States. U.S. EPA, National Health and Environmental Effects Research Laboratory, Corvallis, Oregon, U.S..

• Winward, A. 2007. Boulder, Squaretop Area Field Notes. Field Notes. Unpublished.

Contributors

Bryan Christensen
Karen J. Clause

Approval

Kirt Walstad, 9/28/2023

Acknowledgments

Shari Meeks, SCCD
Troy Fieseler, WGFD
Justin Feeman, BLM