Physiographic features

This site occurs on nearly level flats and bench lands to rolling and somewhat broken foothills. Slopes predominantly range from 5 to 25 percent, and occasionally go up to 35 percent. Small lava rock outcrop areas may be scattered throughout the site. Elevation ranges from 4000 to 5500 feet (1200 to 1680 meters).

Table 2. Representative physiographic features

Climatic features

The Big and Little Wood River Foot slopes and Plains, proposed as MLRA 10X, has a mean elevation of 5310 feet above sea level, and varies from 3600 to 9235 feet. In general, average annual precipitation is greatest on the western side, with the southeast area being the driest. The average annual precipitation, based on 7 long term climate stations located throughout the MLRA, is 15.39 inches, with a range of 12.5 to 18 inches. Monthly precipitation is generally greatest at the end of the year, diminishes steadily until a low in July and August, then increases rapidly in the autumn.
Monthly temperatures can vary considerably. Highs of up to 102° and lows down to -52° Fahrenheit have been recorded. The average annual temperature is 42.9°. The frost-free period ranges from 75 to 98 days. The freeze-free period is a bit longer: 106 to 133 days.
Both morning and afternoon average relative humidity values peak in the winter, and reach their low in July and august. The average number of sunny, cloud-free days is above average for the summer months, but below average for the period from November through February.

Table 3. Representative climatic features

Influencing water features

This site is not influenced by adjacent streams or run on.

Wetland description

This site is not influenced by adjacent wetlands.

Soil features

The soils on this site are silt loams over 20 inches deep to a duripan. The soils are well drained to either bedrock or a duripan. Permeability is impermeable to moderate with available water capacity low to moderate. The moisture supplying capacity of the soils is limited by the depth to the duripan. Water erosion can be high when the plant cover is reduced. These soils are characterized by an aridic soil moisture regime or aridic that borders on xeric. The soil temperature regime is mesic or frigid.

Table 4. Representative soil features

Animal community

Wildlife Interpretations
Animal Community – Wildlife Interpretations

This rangeland ecological site provides diverse habitat for many native wildlife species. Large herbivore use of this ecological site is dominated by mule deer, pronghorn antelope, and elk. Important seasonal habitat is provided for resident and migratory animals including western toad, sagebrush lizard, western rattlesnake, shrews, bats, jackrabbits, ground squirrels, mice, coyote, red fox, badger, sage-grouse, Ferruginous hawk, prairie falcon, horned lark and western meadowlark. Changes in the plant community composition can reduce the number and diversity of wildlife species in the area. With reduced shrub cover shrub obligate avian and mammal species become rare including sage-grouse, brewer’s sparrow, sage thrasher and pygmy rabbits. Encroachment of noxious and invasive plant species (cheatgrass, Rush skeleton weed, and knapweed) can replace native plant species which provide critical feed, brood-rearing and nesting cover for a variety of native wildlife. The loss of herbaceous (grass and forbs) understory vegetation can have a negative impact on ground nesting birds, while the loss of shrub cover negatively affects both ground and shrub nesting avians. Water is limited, being provided only by seasonal runoff, artificial water catchments and spring sites. This rangeland ecological site is commonly associated with pre-historic lava flows which provide unique cave habitats for several sensitive animal species, including the blind cave leiodid beetle, cave obligate mite, bats and cave obligate harvestman.

State 1 Phase 1.1 - Wyoming Big Sagebrush/ Bluebunch Wheatgrass/ Sandberg Bluegrass/ Nevada Bluegrass Reference Plant Community (RPC): This plant community provides a diversity of grasses, forbs and shrubs, used by native insect communities that assist in pollination. The reptile and amphibian community is represented by leopard lizard, short horned lizard, sagebrush lizard, western skink, western rattlesnake, western toad, boreal chorus frog and northern leopard frog. Amphibians are associated with springs and isolated water bodies adjacent to this plant community. Shrub-steppe obligate avian species include the Brewer’s sparrow, sage sparrow, sage thrasher and sage-grouse. Critical habitat (lek sites, nesting areas, winter cover and food) for sage-grouse is provided by this diverse plant community. The plant community supports the needs of large mammals (mule deer, antelope, and elk) providing food and cover on a seasonal basis. Wyoming big sagebrush is preferred browse for ungulates. A diverse small mammal population including golden-mantled ground squirrels, chipmunks and yellow-bellied marmots utilize this community.

State 1 Phase 1.2 - Wyoming Big Sagebrush/ Sandberg Bluegrass Plant Community: This plant community is the result of improper grazing management. An increase in canopy cover of sagebrush contributes to a sparse herbaceous understory. Grasses, forbs and shrubs, are used by native insects that assist in pollination but the reduced herbaceous understory results in less diversity and numbers of insects. The reptile and amphibian community is represented by leopard lizard, short horned lizard, sagebrush lizard, western skink, western rattlesnake, western toad, boreal chorus frog, and northern leopard frog. Diversity and populations of reptiles and amphibians may be reduced due to reduced prey species and cover. Reduced herbaceous understory is a key factor in limiting the use of this plant community by avian species. Key shrub-steppe avian obligates include Brewer’s sparrow, sage sparrow, sage thrasher and sage-grouse. Critical habitat (lek sites, nesting areas, winter cover and food) for sage-grouse is limited due to a less diverse herbaceous plant community. The plant community supports seasonal needs of large mammals (mule deer, antelope, and elk) providing food and cover. Wyoming big sagebrush is preferred browse for these wild ungulates. A diverse small mammal population including golden-mantled ground squirrels, chipmunks and yellow-bellied marmots utilize this plant community.

State 1 Phase 1.3 - Bluebunch Wheatgrass/ Sandberg Bluegrass/ Bottlebrush Squirreltail Plant Community: This plant community is the result of fire. The plant community, dominated by herbaceous vegetation with little or no sagebrush provides less vertical structure and limits use by shrub obligate animals. Insect diversity would be reduced but a diverse native forb plant community would still support select pollinators. Cave dwelling insects and mammals from adjacent habitats would be supported by this plant community. Reptile use, including short horned lizard, sagebrush lizard and western rattlesnakes, would be limited or excluded due to the absence of sagebrush. The dominance of herbaceous vegetation with little sagebrush canopy cover would prevent use of these areas for nesting by Brewer’s sparrow, sage sparrow, sage thrasher, and sage-grouse. This plant community provides brood-rearing habitat for sage-grouse when sagebrush cover is nearby. Winter habitat and nesting cover for sage-grouse has been eliminated. The dominant herbaceous vegetation improves habitat for grassland avian species (horned lark and western meadowlark). Large mammal (mule deer, antelope, and elk) foraging would be seasonal but this community would offer little thermal cover and young of year cover. Small mammal diversity would be reduced and the reduced sagebrush density would not provide suitable habitat for pygmy rabbits.

State 2 - Sandberg Bluegrass/ Cheatgrass/ Bulbous Bluegrass and Annual Plant Community: This plant community is the result of continued improper grazing management and/or frequent fire. The loss of the native shrub and herbaceous plant community would not support a diverse insect community. The reduced forb component in the plant community would support a very limited population of pollinators. Most native reptilian species are not supported with food, water or cover. This plant community does not support the habitat requirements for sage-grouse, sage thrasher, Brewer’s sparrow or sage sparrow. Diversity of grassland avian species is reduced due to poor cover and food. Birds of prey including hawks and falcons may range throughout these areas looking for prey species. Large mammals may utilize the herbaceous vegetation in the early part of the year when the invasive annuals (cheatgrass) are more palatable. At other times of the year large mammals would not regularly utilize these areas due to poor food and cover conditions. The reduction of insect populations and diversity would reduce suitability of the site for bats. The diversity and populations of small mammals would be dominated by open grassland species like the Columbian ground squirrel.

State 3 - Range Seeding Plant Community: The seeding mixture (native or non-native) determines the animal species that would utilize this site. A diverse seed mixture of grasses and forbs would provide similar habitat conditions as in the herbaceous plant community described in State 1 phase 1.3. A diverse seed mixture of grasses, forbs and shrubs would provide similar habitat conditions as described in State 1 phase 1.1 or 1.2. A monoculture of non-native grass species would not support diverse populations of insects, reptiles, avians, mammals or sagebrush obligate species. Grassland animal species including western meadowlark, horned lark, savannah sparrow, deer mouse, kangaroo rat and elk would utilize this site for nesting and/or foraging. Birds of prey including hawks and falcons may range throughout this community looking for prey species.

Grazing Interpretations.

This site is suited for livestock in spring, summer and fall. If water is available, the site is easily grazed by livestock due to gentle slopes.
Estimated initial stocking rate will be determined with the landowner or decision-maker. They will be based on the inventory which includes species, composition, similarity index, production, past use history, season of use and seasonal preference.

Hydrological functions

The hydrologic condition of rangelands is the result of complex interrelationships of soil, vegetation, topography and climate. The hydrology of this site is characterized by low intensity frontal storms from October through April, and occasional high intensity thunderstorms during summer. Approximately 50 percent comes during the plant growing season, with May and June as the wettest months. About 25 to 35 percent of the precipitation falls as snow, and snow depth especially at lower elevations is not sufficient to insulate the soils from freezing. Soil frost influences runoff and infiltration, and freezing and thawing cycles can maintain a saturated soil condition which leads to breakdown of soil aggregates. Wyoming big sagebrush sites at elevations ranging from 4,000 to 5,500 feet on these loamy sites typically generate little runoff. Macropore flow is an important process on this site, where water flows in interspace “channels” or low areas, and is intercepted by shrub coppices with higher infiltration rates. Runoff averages about 3 percent of the annual water budget. Ponding and flooding generally do not occur on this site. Run-on from adjacent sites normally does not occur.

1.1 Reference Plant Community
In this community, especially on less steep slopes, the majority of rainfall and snowmelt infiltrates into the soil profile and the erosion potential is very low. Shrub canopy zones (coppices) generally have higher rates of infiltration than shrub interspaces because of differences in soil morphology, organic matter and surface litter cover. Moss and lichens dominate most coppices as ground cover. Interspaces between shrubs are either bare or partially covered with rock or litter. Moss in the sagebrush understory is a good indicator of proper hydrologic function. Dominance of bluebunch wheatgrass in the understory is also an indicator of good hydrologic condition. When soil surface condition is dry, and undecomposed litter biomass accumulates, water repellency can develop on lighter textured soils. Little runoff occurs from this site, especially at lower slopes. When runoff does occur, it is typically in late spring and is associated with snowmelt or rainfall on frozen soils. Occasional large thunderstorms will generate runoff in summer. Very little sediment is delivered off-site. When sediment loss does occur, it is usually in late winter when soil aggregate stability is lowest, or in summer when dry conditions increase repellency. Deep percolation (less than one percent of water budget) does not generally occur on this site, due to low precipitation and the presence of duripans.

Plant Community 1.2
Increasing sagebrush density and cover, due to the lack of fire or improper grazing management, is associated with deteriorating hydrologic condition. Increasing water repellency and subsequently higher runoff rates are associated with litter buildup in decadent Wyoming big sagebrush coppice microsites. Repellency typically increases during dry conditions, so that runoff and erosion are more likely to occur from smaller and/or less intense storm events. Studies show increasing cover of sagebrush is typically correlated with greater sediment/runoff ratios. The loss of vigorous deep-rooted bunchgrasses in conjunction with invading annual grasses is indicative of reduced infiltration capacity. Dominance of Sandberg bluegrass in the understory is also correlated with higher runoff rates. The presence of increased shrub cover, including taller shrubs, increases the chance of interception loss. Chemical brush management should have minimal impact on sagebrush hydrology if other factors remain undisturbed (coppice characteristics remain intact, with little impact on litter cover), and will invigorate native bunchgrasses if managed properly. Prescribed burns are best used to create mosaics on these Wyoming big sage brush sites, where it may take 20 to 40 years for recovery following fire, regardless of intensity. Disturbance increases the risk of invasion by annuals.

Plant Community 1.3
Fire can reduce infiltration and increase runoff and erosion causing reduced site productivity and contributing to water quality impacts. Fire reduces random roughness and significantly reduces plant cover, litter biomass, and organic matter in the soil surface. Burning also reduces macrofauna populations that contribute to increased aggregate stability through secreted compounds and fungal hyphae production. Where litter cover remains intact, fire impacts are reduced. The effects of fire on the risk of runoff and erosion will be significant on steeper sites until ground and canopy cover recover. Amount of runoff and erosion will depend on the weather pattern during the recovery period. Under severe burn conditions, the probability of erosion exceeding 2.5 tons/acre the year following the burn is approximately 20% given typical weather patterns and burn conditions. After fire, water repellency often occurs on the soil surface, with burned coppices being most impacted. Mosaic burn patterns on a pre-fire HCPC site will somewhat mitigate erosion and runoff effects. Repellency is typically gone after two to three seasons following fire, and hydrologic function improves significantly. Good grazing management that addresses frequency, duration, and intensity of grazing can keep fine fuels from developing and promote native bunchgrasses. Recovered sites with bluebunch wheatgrass dominating the understory have good hydrologic function. Gradual increases in Wyoming big sagebrush will tend to reduce fire frequency. These sites typically take 20 to 40 years for sagebrush canopy to regain pre-fire cover levels.


State 2
Litter cover can be reduced by 50% and bare ground can increase to over 70% immediately following fire. Repeated fires significantly reduce site productivity. Dominance of annual grass and forbs is typical, and is associated with unstable hydrologic conditions. Due to diffuse basal characteristics, annual grasses generally do not have the capacity to catch and hold sediment like bunchgrass clumps. There is no shrub cover and little understory to mitigate the impact of rainfall on soil, which leads to increased soil detachment and availability for transport. While rock cover, when present, may reduce detachment, it reduces infiltration and speeds delivery and transport of sediment. Wyoming big sagebrush sites often have higher erodibility than other sagebrush sites, and have the potential to produce significant amounts of sediment loss during larger storm events. This is correlated with less litter, grass cover, and more bare ground on these frequently burned sites. In heavy stands of cheatgrass and other annual species, runoff potential is reduced during spring and early summer. Fire risk can be high, especially when conditions are dry. More frequent fires result in increased bare ground conditions which are highly susceptible to water and wind erosion. Repeated cycles of annual grass regeneration and repeated fire can result in severe depletion of the surface soil horizon and organic matter. Reductions in organic matter lead to reduced aggregate stability, reducing infiltration and plant available water, and increasing the risks of runoff and soil loss. Reduced cover and reduced random roughness due to repeated burns provide interconnected flow paths for runoff and associated erosion. Sediment yields increase as rill processes become dominant. With improper grazing management, trail areas become compacted, leading to further rill and gully creation.


State 3
Seeding is not likely to reduce runoff or erosion in the year following a burn. Seeding of native or desired species, if successful, will help stabilize the erosion process and improve hydrologic conditions over time. As sagebrush and other shrubs establish, hydrologic function of this state will approach Reference if significant soil loss has not occurred prior to seeding. Where shrubs successfully establish or increase naturally into the seeding, the site will be less prone to freeze-thaw processes and some snow will accumulate during winter storms. Seeding and restoration of the site will be dependent on how far the site productivity and hydrologic condition has diminished before management.

Recreational uses

The site has some hiking and horseback opportunities. ATV’s use the site due to its gentle slopes.

Wood products

None

Other products

None

Other information

Field Offices:

Mountain Home,ID
Gooding,ID
Fairfield,ID
Shoshone,ID
Rupert,ID
Arco,ID

Inventory data references

Information presented here has been derived from NRCS clipping and other inventory data. Also, field knowledge of range-trained personnel was used. Those involved in developing this site description include:
Dave Franzen, co-owner, Intermountain Rangeland Consultants, LLC
Jacy Gibbs, co-owner, Intermountain Rangeland Consultants, LLC
Jim Cornwell, Range Management Specialist, IASCD
Brendan Brazee, State Rangeland Management Specialist, NRCS, Idaho
Lee Brooks, Range Management Specialist, IASCD
Frank Fink, State Biologist, NRCS, Idaho
Dee Carlson,Water Quality Specialist, NRCS, Idaho
Jerry Korol, GIS Specialist, NRCS, Idaho

References

• . 2004. Restoring Western Ranges and Wildlands. General Technical Report RMRS-GTR-136 Vols 1-3. USDA Forest Service, Rocky Mountain Research Station.

Other references

Hironaka, M., M.A. Fosberg, A. H. Winward. 1983. Sagebrush- Grass Habitat Types of Southern Idaho. University of Idaho. Moscow, Idaho. Bulletin Number 35

USDA, NRCS.2001. The PLANTS Database, Version 3.1 (http://plants.usda.gov.). National Plant Data Center, Baton Rouge, LA 70874-4490 USA
USDA, Forest Service, Fire Effects Information Database. 2004. www.fs.fed.us/database/feis

SPUR 2000 (simulation model), Version F1.0, USDA-ARS, Northwest Watershed Research Center.

Wilcox, BP, MS Seyfried, KR Cooley, and CL Hanson. 1991. Runoff characteristics of sagebrush rangelands: Modeling implications. JSWC 46: 153-158.

Wilcox, BP, MK Wood, and JM Tromble. 1988. Factors influencing infiltrability of semiarid mountain slopes. JRM 41: 197-206.

MS Seyfried. 1991. Infiltration patterns from simulated rainfall on a semiarid rangeland soil. Journal SSSA 55: 1726-1734.

Dunne, T, W. Zhang, and BF Aubry. 1991. Effects of rainfall, vegetation, and microtopograpy on infiltration and runoff. WRR 27: 2271-2285.

Pierson, FB, WH Blackburn, and JC Wood. 1994. Incorporating small scale spatial variability into predictions of hydrologic response on sagebrush rangelands. SSSA Spec Pub 38. pp23-34.

Pierson, FB, KE Spaeth, ME Weltz, and DH Carlson. 2002. Hydrologic response of diverse western rangelands. JRM 55:558-570.

Moffet, CA, FB Pierson, PR Robichaud, KE Spaeth, and SP Hardegree.2007. Modeling soil erosion on steep sagebrush rangeland before and after prescribed fire. Catena 71:218-228.

Branson, FA, GF Gifford, KG Renard, and RF Hadley. 1981. Rangeland Hydrology. Kendall Hunt Publishing Co., Iowa.

Spaeth, KE, FB Pierson, and CA Moffet. 2006. Hydrology, erosion, and soil interrelationships after rangeland wildfire. In: Proc. 3rd Nat. Conf. on Grazing Lands, Dec 13-16, St Louis, MI.

Contributors

Dave Franzen
Jacy Gibbs

Approval

Kirt Walstad, 12/13/2023