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Ecological site EX044B01A138

Shallow Droughty (SwDr) LRU 01 Subset A

Last updated: 9/08/2023
Accessed: 11/23/2024

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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.

MLRA notes

Major Land Resource Area (MLRA): 044B–Central Rocky Mountain Valleys

Major Land Resource Area (MLRA) 44B, Central Rocky Mountain Valleys, is nearly 3.7 million acres of southwest Montana and borders two MLRAs: 43B Central Rocky Mountains and Foothills and 46 Northern and Central Rocky Mountain Foothills.

The major watersheds of this MLRA are those of the Missouri and Yellowstone Rivers and their associated headwaters such as the Beaverhead, Big Hole, Jefferson, Ruby, Madison, Gallatin, and Shields Rivers. These waters allow for extensive irrigation for crop production in an area that would generally only be compatible with rangeland and grazing. The Missouri River and its headwaters are behind several reservoirs that supply irrigation water, hydroelectric power, and municipal water. Limited portions of the MLRA are west of the Continental Divide along the Clark Fork River.

The primary land use of this MLRA is production agriculture (grazing, small grain production, and hay), but there is some limited mining. Urban development is high with large expanses of rangeland converted to subdivisions for a rapidly growing population.

The MLRA consists of one Land Resource Unit (LRU) and seven climate based LRU subsets. These subsets are based on a combination of Relative Effective Annual Precipitation (REAP) and frost free days. Each subset expresses a distinct set of plants that differentiate it from other LRU subsets. Annual precipitation ranges from a low of 9 inches to a high near 24 inches. The driest areas tend to be in the valley bottoms of southwest Montana in the rain shadow of the mountains. The wettest portions tend to be near the edge of the MLRA at the border with MLRA 43B. Frost free days also vary widely from less than 30 days in the Big Hole Valley to around 110 days in the warm valleys along the Yellowstone and Missouri Rivers.

The plant communities of the MRLA are highly variable, but the dominant community is a cool-season grass and shrub-steppe community. Warm-season grasses have an extremely limited extent in this MLRA. Most subspecies of big sagebrush are present, to some degree, across the MLRA.

LRU notes

MLRA 44B has one LRU that covers the entire MLRA. The LRU has been broken into seven climate subsets based on a combination of Relative Effective Annual Precipitation (REAP) and frost free days. Each combination of REAP and frost free days results in a common plant community that is shared across the subset. Each subset is giving a letter designation of A through F for sites that do not receive additional water and Y for sites that receive additional water.

LRU 01 Subset A has a REAP of nine to 14 inches (228.6-355.6mm) with a frost free days range of 70 to 110 days. This combination of REAP and frost free days results in a nearly treeless sagebrush steppe landscape.

The soil moisture regime is Ustic, dry that borders on Aridic and has a Frigid soil temperature regime.

Classification relationships

Mueggler and Stewart. 1980. Grassland and Shrubland habitat types of Western Montana
1. Stipa comata/Bouteloua gracilis h.t.
2. Agropyron spicatum/Bouteloua gracilis h.t.

Montana Natural Heritage Program Vegetation Classification
1. Stipa comata - Bouteloua gracilis Herbaceous Vegetation
(STICOM – BOUGRA) Needle and thread/Blue grama
Natural Heritage Conservation Rank-G5 / S5
Edition / Author- 99-11-16 / S.V. Cooper,

EPA Ecoregions of Montana, Second Edition:
Level I: Northwestern Forested Mountains
Level II: Western Cordillera
Level III: Middle Rockies & Northern Great Plains
Level IV: Paradise Valley
Townsend Basin
Dry Intermontane Sagebrush Valleys
Shield-Smith Valleys

National Hierarchical Framework of Ecological Units:
Domain: Dry
Division: M330 – Temperate Steppe Division – Mountain Provinces
Province: M332 –Middle Rocky Mountain Steppe – Coniferous Forest – Alpine Meadow
Section: M332D – Belt Mountains Section
M332E – Beaverhead Mountains Section
Subsection: M332Ej – Southwest Montana Intermontane Basins and Valleys
M332Dk – Central Montana Broad Valleys

Ecological site concept

The Shallow Droughty ecological site is an upland site formed from residuum of non-carbonatic geology. The site does not receive additional moisture from a water table or flooding. It has 32 percent or less clay in the upper four (4) inches of the mineral surface. It is a shallow site and has a bedrock, lithic, or paralithic root-restrictive layer within 20 inches (50cm). The surface of the site has less than 15 percent stone. The Shallow Droughty is skeletal, with less than 35 percent rock fragments in the 10 to 20-inch depth. The site does not have a saline or saline-sodic influence and is not strongly or violently effervescent within four inches of the mineral surface. Calcium carbonates may increase with depth.

Associated sites

EX044B01A036	Droughty (Dr) LRU 01 Subset A This site exists in the same landscape as droughty
EX044B01A038	Droughty Steep (DrStp) LRU 01 Subset A Droughty Steep often resides lower on the landscape as the Shallow, Droughty site on slopes greater than 15 percent
EX044B01A136	Shallow Loamy (SwLo) LRU 01 Subset A The Shallow, Loamy and Shallow Droughty sites exist on the same landscape and are often neighboring sites

EX044B01A036

Droughty (Dr) LRU 01 Subset A

This site exists in the same landscape as droughty

EX044B01A038

Droughty Steep (DrStp) LRU 01 Subset A

Droughty Steep often resides lower on the landscape as the Shallow, Droughty site on slopes greater than 15 percent

EX044B01A136

Shallow Loamy (SwLo) LRU 01 Subset A

The Shallow, Loamy and Shallow Droughty sites exist on the same landscape and are often neighboring sites

Similar sites

EX044B01A036	Droughty (Dr) LRU 01 Subset A Droughty produces a similar plant community however does not have a root restrictive layer which allows for greater production and a slightly more resilient plant community
EX044B01A136	Shallow Loamy (SwLo) LRU 01 Subset A The Shallow, Loamy site shares a similar plant community and similar STMs concept

EX044B01A036

Droughty (Dr) LRU 01 Subset A

Droughty produces a similar plant community however does not have a root restrictive layer which allows for greater production and a slightly more resilient plant community

EX044B01A136

Shallow Loamy (SwLo) LRU 01 Subset A

The Shallow, Loamy site shares a similar plant community and similar STMs concept

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Artemisia tridentata (2) Tetradymia canescens
Herbaceous	(1) Pseudoroegneria spicata (2) Hesperostipa comata

Legacy ID

R044BA138MT

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Physiographic features

This ecological site occurs on nearly level to very steep hills, escarpments, and buttes. It often occurs in complexes with other ecological sites. This site can be found on all slopes and exposures, but it is most common on slopes lower than 25 percent. Aspect can have an impact on the composition and production of plant communities. The amount of rock outcrop tends to increase as slopes increase.

Table 2. Representative physiographic features

Geomorphic position, hills	(1) Crest
Landforms	(1) Intermontane basin > Escarpment (2) Intermontane basin > Butte (3) Intermontane basin > Ridge (4) Intermontane basin > Hill
Runoff class	Medium to high
Elevation	1,280 – 1,981 m
Slope	2 – 25%
Aspect	W, NW, N, NE, E, SE, S, SW

Table 3. Representative physiographic features (actual ranges)

Runoff class	Not specified
Elevation	Not specified
Slope	0 – 45%

Climatic features

The Central Rocky Mountain Valleys MLRA has a continental climate. Fifty to sixty percent of the annual long-term average total precipitation falls between May and August. Snow on frozen ground makes up the majority of winter precipitation. Average precipitation for LRU 01 Subset A is 12 inches (305mm), and the frost-free period averages 78 days. Precipitation is highest in May and June. Some of Montana’s driest areas are located in sheltered mountain valleys because of the rain-shadow effects on the leeside of some ranges.

Table 4. Representative climatic features

Frost-free period (characteristic range)	70-110 days
Freeze-free period (characteristic range)	110-140 days
Precipitation total (characteristic range)	229-356 mm
Frost-free period (actual range)	70-110 days
Freeze-free period (actual range)	110-140 days
Precipitation total (actual range)	229-356 mm
Frost-free period (average)	78 days
Freeze-free period (average)	125 days
Precipitation total (average)	305 mm

Characteristic range

Actual range

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Figure 1. Monthly precipitation range

Characteristic range

Actual range

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Figure 2. Monthly minimum temperature range

Characteristic range

Actual range

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Figure 3. Monthly maximum temperature range

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Figure 4. Monthly average minimum and maximum temperature

Figure 5. Annual precipitation pattern

Figure 6. Annual average temperature pattern

Climate stations used

(1) DEER LODGE 3 W [USC00242275], Deer Lodge, MT
(2) DILLION U OF MONTANA WESTERN [USC00242409], Dillon, MT
(3) GLEN 2 E [USC00243570], Dillon, MT
(4) ENNIS [USC00242793], Ennis, MT
(5) BOULDER [USC00241008], Boulder, MT
(6) GARDINER [USC00243378], Gardiner, MT
(7) TOWNSEND [USC00248324], Townsend, MT
(8) TRIDENT [USC00248363], Three Forks, MT
(9) TWIN BRIDGES [USC00248430], Sheridan, MT
(10) WHITE SULPHUR SPRNGS 2 [USC00248930], White Sulphur Springs, MT
(11) DILLON AP [USW00024138], Dillon, MT
(12) HELENA RGNL AP [USW00024144], Helena, MT

Influencing water features

The site has a root-restrictive layer that may affect water infiltration; however, the site is considered water-limited due to its low available water holding capacity. Runoff is medium to high.

Wetland description

This site is not associated with wetlands characteristics.

Soil features

These soils are shallow (10 to 20 inches deep to root restrictive layer), moderate to moderately rapid permeability, and are well to somewhat excessively drained. These soils formed from residuum from mixed origins primarily from non-calcareous geology. Typically soil surface textures consist of loam, clay loam, and silt loam textures. Soils may have gravelly surface however will vary depending on its association with to a neighboring sites. The 10- to 20-inch section of the soil below the surface will have greater than 35 percent rock fragments. Common soils series in this ecological site includes Blackleaf and Gnojek. These soils may exist across multiple ecological sites due to natural variations in slope, texture, rock fragments, and pH.

Table 5. Representative soil features

Parent material	(1) Residuum – igneous, metamorphic and sedimentary rock
Surface texture	(1) Loam (2) Silt loam (3) Clay loam
Drainage class	Well drained to somewhat excessively drained
Permeability class	Moderate to moderately rapid
Depth to restrictive layer	25 – 51 cm
Soil depth	25 – 51 cm
Surface fragment cover <=3"	0 – 28%
Surface fragment cover >3"	0 – 5%
Available water capacity (0-50.8cm)	2.03 – 7.37 cm
Soil reaction (1:1 water) (0-50.8cm)	6.6 – 8
Subsurface fragment volume <=3" (25.4-50.8cm)	15 – 40%
Subsurface fragment volume >3" (25.4-50.8cm)	0 – 15%

Ecological dynamics

The Shallow Droughty ecological site of MLRA 44B in the 9 to 14 inch climatic subset shares plant communities and state and transition model with Shallow Loamy and Shallow Droughty ecological sites in both MLRAs 44B and 43B in the 9 to 14 inch climatic subset. These sites are nearly indistinguishable.

The reference plant community is dominated by bluebunch wheatgrass (Pseudoroegneria spicata) and needle and thread (Hesperostipa comata). Subdominant species may include green needlegrass (Nassella viridula), gray horsebrush (Tetradymia canescens), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), and Indian ricegrass (Achnatherum hymenoides).

Natural fire was a major ecological driver of this entire ecological site. Fire tended to restrict tree and sagebrush growth to small patches and promote an herbaceous plant community. The natural fire return interval was highly variable, ranging up to 100 years; however, it was likely shorter than 35 years (Arno and Gruell 1983). Since 1910, there has been a significant increase in the suppression of fire in sagebrush and trees.

Wyoming big sagebrush steppe communities historically had low fuel loadings and were characterized by 10- to 70-year fire intervals that produced a mosaic of burned and unburned lands (Bunting et al., 1987). A shift to the dominance of shrubs may occur in response to improper grazing management, drought, or where big sagebrush occurs due to a lack of fire. Shrub encroachment by a variety of species, including broom snakeweed (Gutierrezia sarothrae), fringed sagewort (Artemisia frigida), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), rubber rabbitbrush (Ericameria nauseosa), green rabbitbrush (Chrysothamnus viscidiflorus), and plains prickly pear cactus (Opuntia polyacantha) occurs within this site as the mid-stature bunchgrasses decrease. Shrub dominance and grass loss can be associated with soil erosion and, ultimately, thinning of the native soil surface. Subsequent loss of soil could lead to a Degraded State. All states could also lead to the Invaded State when there is a lack of weed prevention and control measures.

Historical records indicate that, prior to the introduction of livestock (cattle and sheep) during the late 1800s, elk and bison grazed this ecological site. Because of the nomadic nature and herd structure of bison, grazed areas received periodic high intensity, short duration grazing pressure.Forage for livestock was noted as minimal in areas recently grazed by bison (Lesica and Cooper 1997). Meriwether Lewis documented that he was met by 60 Shoshone warriors on horseback in August 1805, and the Corps of Discovery was later supplied with horses by the same band of Shoshone. This suggests that the areas near the modern-day Montana towns of Twin Bridges, Dillon, Grant, and Dell were grazed by an untold number of horses prior to the large introduction of cattle and sheep. Livestock grazing has occurred on most of this ecological site in southwestern Montana for more than 150 years. The gold boom in the 1860s brought the first herds of livestock overland from Texas, and homesteaders began settling the area. During this time, cattle were the primary domestic grazers in the area. In the 1890s, Montana sheep production began to increase and dominated the livestock industry until the 1930s. Since the 1930s, cattle production has dominated the livestock industry in the region (Wyckoff and Hansen 2001).

Some of the major invasive species that can occur on this site include (but are not limited to) spotted knapweed (Centaurea stoebe), leafy spurge (Euphorbia esula), cheatgrass (Bromus tectorum), field brome (Bromus arevensis), yellow toadflax (Linaria vulgaris), and dandelion (Taraxicum spp.). Invasive weeds are beginning to have a high impact on this ecological site, particularly cheatgrass invasion.

Plant Communities and Transitions
A state and transition model for this ecological site is depicted below. Thorough descriptions of each state, transition, plant community, and pathway follow the model. This model is based on available experimental research, field data, field observations, and interpretations by experts. It is likely to change as knowledge increases.

The plant communities within the same ecological site will differ across the MLRA due to the naturally occurring variability in weather, soils, and aspect. The biological processes on this site are complex; therefore, representative values are presented in a land management context. The species lists are representative and are not botanical descriptions of all species occurring, or potentially occurring, on this site. They are intended to cover the core species and the known range of conditions and responses.

Although there is considerable qualitative experience supporting the pathways and transitions within the state and transition model (STM), no quantitative information exists that specifically identifies threshold parameters between grassland types and invaded types in this ecological site.

State and transition model

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

State 1
Reference State

The Reference State of this ecological site consists of two known potential plant communities 1.1 Bluebunch Community and 1.2 Mixed Bluebunch Community. These are described below but are generally characterized by a mid-statured, cool-season grass communities with limited tree and shrub production. Community 1.1 is dominated by bluebunch wheatgrass and is considered the reference community while Community 1.2 has a codominance of bluebunch wheatgrass and needle and thread with an increase in thickspike wheatgrass and shrubs. These communities may meld into each other due to the varying conditions that occur in southwest Montana particularly during dry cycles where needle and threads' early season growth cycle takes better advantage of the limited moisture.

Community 1.1
Bluebunch Wheatgrass Community

In the Bluebunch Wheatgrass Community, bluebunch wheatgrass (Pseudoroegneria spicata) and needle and thread (Hesperostipa comata) are dominant species. Thickspike wheatgrass, Indian ricegrass (Achnatherum hymenoides), curl-leaf mountain mahogany (Cercocarpus ledifolius), and winterfat (Krascheninnikovia lanata) are subordinates in the community. Other shrub species and low trees remain a minor part of the community. In areas where the soil texture is coarser, spineless horsebrush (Tetradymia canescens) may also occupy a small niche. Sandberg bluegrass (Poa secunda) and dryland sedges are also common. This state occurs on the Shallow Droughty site in areas with light to moderate livestock grazing or in areas receiving only seasonal wildlife grazing. Bluebunch wheatgrass lacks resistance to grazing during the critical growing season (spring) and will decline in vigor and production if grazed in the critical growing season more than one year in three (Wilson et al. 1960). The reference state is moderately resilient and will return to dynamic equilibrium after a relatively short period of stress (such as drought or short-term improper grazing) if favorable or normal growing conditions and properly managed grazing are restored. As discussed in the Ecological Dynamics section, the natural fire regime restricted shrubs to relatively small portions of Reference Plant Community 1.1. Shrub species present may include curl-leaf mountain mahogany, black sagebrush (Artemisia nova), spineless horsebrush, winterfat, tarragon (Artemisia drucunculus), and Wyoming big sagebrush, fringed sagewort, and little sagebrush (Artemisia arbuscula). Frequent fire maintained this community as an open, seral stand of herbaceous species with patches of mountain mahogany and scattered tall shrubs and trees.

Dominant plant species

ponderosa pine (Pinus ponderosa var. scopulorum), tree
Douglas-fir (Pseudotsuga menziesii), tree
Rocky Mountain juniper (Juniperus scopulorum), tree
limber pine (Pinus flexilis), tree
Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), shrub
little sagebrush (Artemisia arbuscula), shrub
yellow rabbitbrush (Chrysothamnus viscidiflorus), shrub
Woods' rose (Rosa woodsii), shrub
spineless horsebrush (Tetradymia canescens), shrub
bluebunch wheatgrass (Pseudoroegneria spicata), grass
needle and thread (Hesperostipa comata), grass
green needlegrass (Nassella viridula), grass
Sandberg bluegrass (Poa secunda), grass
Indian ricegrass (Achnatherum hymenoides), grass
dotted blazing star (Liatris punctata), other herbaceous
American vetch (Vicia americana), other herbaceous
hairy false goldenaster (Heterotheca villosa), other herbaceous
locoweed (Oxytropis), other herbaceous
milkvetch (Astragalus), other herbaceous
arrowleaf balsamroot (Balsamorhiza sagittata), other herbaceous

Figure 7. Annual production by plant type (representative values) or group (midpoint values)

Table 6. Annual production by plant type

Plant type	Low (kg/hectare)	Representative value (kg/hectare)	High (kg/hectare)
Grass/Grasslike	404	633	852
Shrub/Vine	34	67	101
Forb	11	28	45
Tree	–	–	11
Total	449	728	1009

Table 7. Ground cover

Tree foliar cover	0-1%
Shrub/vine/liana foliar cover	1-3%
Grass/grasslike foliar cover	10-15%
Forb foliar cover	1-3%
Non-vascular plants	0-1%
Biological crusts	0-1%
Litter	25-35%
Surface fragments >0.25" and <=3"	0-15%
Surface fragments >3"	0-10%
Bedrock	0%
Water	0%
Bare ground	10-15%

Table 8. Soil surface cover

Tree basal cover	0-1%
Shrub/vine/liana basal cover	10-15%
Grass/grasslike basal cover	65-70%
Forb basal cover	5-10%
Non-vascular plants	0-1%
Biological crusts	0-1%
Litter	25-35%
Surface fragments >0.25" and <=3"	0-15%
Surface fragments >3"	0-10%
Bedrock	0%
Water	0%
Bare ground	10-15%

Figure 8. Plant community growth curve (percent production by month). MT44B032, Dry Uplands. Cool season grass dominated system. Most dry, upland sites located within MLRA 44B LRU A are characterized by early season growth which is mostly complete by Mid-July. Limited fall "green-up" if conditions allow..

Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
J	F	M	A	M	J	J	A	S	O	N	D
			15	30	30	15	5	5

Community 1.2
Mixed Bunchgrass Community

The dominant species in the Mixed Bunchgrass Community (1.2) is a diverse and complex plant community similar to the Bluebunch Wheatgrass Community (1.1). Without active management, the site is not likely to return to the reference plant community. Needle and thread tolerates grazing pressure better than bluebunch wheatgrass. The growing point for bluebunch wheatgrass grass is several inches above the ground, making it very susceptible to continued close grazing (Smoliack et al., 2006), while needle and thread growing points tend to be near the plant base. These plants increase in composition when less palatable and less grazing-tolerant plants decrease due to improper grazing management. Needle and thread and bluebunch wheatgrass share dominance in the Mixed Bunchgrass Community (1.2). Other grass species that are more tolerant of grazing and are likely to increase in number compared to the Reference Plant Community include Sandberg bluegrass (Poa secunda), prairie Junegrass, thickspike wheatgrass (Elymus lanceolatus), and blue grama (Bouteloua gracilis). Some increaser forb species include western yarrow, spiny phlox (Phlox hoodii), scarlet globemallow (Sphaeralcea coccinea), hairy goldenaster (Heterotheca villosa), and pussytoes (Antennaria spp.). Fringed sagewort (Artemisia frigida) is a shrub that also increases under prolonged drought or heavy grazing and can respond to precipitation that falls in July and August. Trees may be part of this plant community as a result of long-term fire suppression. Douglas fir and Rocky Mountain Juniper will be the most common species; however, ponderosa pine (Pinus ponderosa) and limber pine (Pinus flexilis) may also be present depending on associated seed sources. Tree coverage is very limited, often less than two stems per acre. Heavy, continuous grazing will reduce plant cover, litter, and mulch. The timing of grazing is important on this site because of the moisture limitations beyond June, especially on the drier sites. Bare ground will increase, exposing the soil to erosion. Litter and mulch will be reduced as plant cover declines. As long as the production of Bluebunch wheatgrass remains a significant portion of the total biomass production, the site can return to the Bluebunch Wheatgrass Community (Pathway 1.2A) under proper grazing management and favorable growing conditions. Needle and thread will continue to increase until they make up 50 percent or more of the grass composition. Once bluebunch wheatgrass has been reduced to less than 15 percent composition, it may be difficult (possibly impossible) for the site to recover to Bluebunch Wheatgrass Community (1.1). The risk of soil erosion increases when canopy cover decreases below 50 percent. As soil conditions degrade, there will be a loss of organic matter, reduced litter, and reduced soil fertility. Degraded soil conditions increase the difficulty of reestablishing bluebunch wheatgrass and returning to the Bluebunch Wheatgrass Community (1.1). The Mixed Bunchgrass Community (1.2) is the at-risk plant community for this ecological site. When overgrazing continues, increaser species such as needle and thread and native forb species will become more dominant, and this triggers the change to the Altered State (2) or the Degraded State (3). Until the Mixed Bunchgrass Community (1.2) crosses the threshold into the Needle and Thread Community (2.1) or the Invaded Community (4.1), this community can be managed toward the Bluebunch Wheatgrass Community (1.1) using prescribed grazing and strategic weed control (if present). It may take several years to achieve this recovery, depending on growing conditions, the vigor of remnant bluebunch wheatgrass plants, and the aggressiveness of the weed treatments.

Pathway 1.1a
Community 1.1 to 1.2

Bluebunch wheatgrass loses vigor with improper grazing or extended drought. When vigor declines enough for plants to die or become smaller, species with higher grazing tolerance increase in vigor and production as they access the resources previously used by bluebunch wheatgrass. The decrease in species composition by weight of bluebunch wheatgrass to less than 25 percent indicates that the plant community has shifted to the Mixed Bunchgrass Community (1.2). The driver for community shift 1.1A is improper grazing management or prolonged drought. This shift is triggered by the loss of vigor of bluebunch wheatgrass, soil erosion, or prolonged drought coupled with improper grazing. Blaisdell (1958) stated that drought and warmer-than-normal temperatures are known to advance plant phenology by as much as one month. During drought years, plants may be especially sensitive or reach a critical stage of development earlier than expected. Since needle and thread normally begins growth earlier and heads out in June while bluebunch wheatgrass heads out in July, this should be taken into consideration when planning grazing management.

Pathway 1.2a
Community 1.2 to 1.1

The Mixed Bunchgrass Community (1.2) will return to the Bluebunch Wheatgrass Community (1.1) with proper grazing management and appropriate grazing intensity. Proper grazing management entails balancing grazing timing, frequency, and duration/intensity to match the community's ability to recover from grazing events. Favorable moisture conditions will facilitate or accelerate this transition. It may take several years of favorable conditions for the community to transition back to a bluebunch dominated state. The driver for this community shift (1.2a) is the increased vigor of bluebunch wheatgrass, to the point that it represents more than 50 percent of species composition. The trigger for this shift is the change in grazing management favoring bluebunch wheatgrass. These triggers are generally conservative grazing management styles such as deferred or rest rotations utilizing moderate grazing (less than 50 percent utilization) combined with favorable growing conditions such as cool, wet springs. These systems tend to promote increases in soil organic matter, which promotes microfauna and can increase infiltration rates. Inversely, long periods of rest at a time when this state is considered stable may not result in an increase in bluebunch wheatgrass, and it has been suggested (Noy-Meir 1975) that these long periods of rest or underutilization may actually drive the system to a lower level of stability by creating large amounts of standing biomass, dead plant caudex centers, and gaps in the plant canopy.

State 2
Altered State

This state is characterized by having less than 10 percent bluebunch wheatgrass by dry weight. It is represented by one community. Production in this state can be similar to that in the Reference State (1). Some native plants tend to increase under prolonged drought and heavy grazing practices. These species may include needle and thread, Sandberg bluegrass, scarlet globemallow, hairy goldenaster, fringed sagewort, Rocky Mountain juniper, and Douglas fir. Heavy grazing is defined as grazing that exceeds the plant community's ability to recover. Often, this level for this ecological site is grazing above 50 percent utilization without post-grazing rest or deferment.

Community 2.1
Increaser Grass-Shrub Community

Long-term grazing mismanagement with continuous growing-season grazing pressure will reduce total productivity of the site and lead to an increase of bare ground. Once plant cover is reduced, the site is more susceptible to erosion and degradation of soil properties. Soil erosion or reduced soil health will result in reduced plant production. This soil erosion or loss of soil fertility indicates the transition to the Altered State (2), because it creates a threshold requiring input of energy to return to the Reference State (1). Transition to the Increaser Grass-Shrub Community (2.1) may be exacerbated by extended drought conditions. Needle and thread dominates this community (2.1). Bluebunch wheatgrass makes up less than 10 percent of the species composition by dry weight, and the remaining bluebunch wheatgrass plants tend to be scattered and low in vigor. Invasive species will become more common, increasing competition for bluebunch wheatgrass. This makes it difficult for bluebunch wheatgrass to quickly respond to a change in grazing management alone. Therefore, an input of energy is required for the community to return to the Reference State (1). Wind and water erosion may be eroding soil from the plant interspaces. Soil fertility is reduced, and soil surface erosion resistance has declined compared to the Reference State (1). This community crossed a threshold compared to the Mixed Bunchgrass Community (1.2) due to the erosion of soil, vegetation composition, loss of soil fertility, or degradation of soil conditions. This results in a critical shift in the ecology of the site. The effects of soil erosion can alter the hydrology, soil chemistry, soil microorganisms, and soil structure to the point where intensive restoration is required to restore the site to another state or community. Changing grazing management alone cannot create sufficient improvement to restore the site within a reasonable time frame. Dormaar (1997) stated that with decreased grazing pressure, a needle and thread/blue grama plant community did not change species composition, but the content of the soil carbon increased. It will require a considerable input of energy to move the site back to the Reference State (1). This state has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require reclamation efforts, i.e., soil rebuilding, intensive mechanical treatments, and reseeding. The transition to this state could result from overgrazing, especially repeated early-season grazing coupled with extensive drought. If heavy grazing continues, plant cover, litter, and mulch will continue to decrease, and bare ground will increase, exposing the soil to accelerated erosion. Litter and mulch will move off-site as plant cover declines. The Increaser Grass-Shrub Community will then shift to a Degraded State (3). Introduction or expansion of invasive species will further drive the plant community into the Invaded State (4).

State 3
Degraded State

The Degraded State is described by a single plant community consisting of nearly equal components of increaser grasses, shrubs, and forbs. Large patches of bare ground exist, with areas of erosional pedestalling and terracettes being common. Dense clubmoss (Selaginella densa) exists between plant bases as a reaction to the increased bare ground. This is a terminal state, meaning that restoration back to the Reference State (1) is not possible as too many ecological processes have been altered and their ability to return to normal has been lost.

Community 3.1
Shortgrass-Shrub Community

Soil loss continues or increases to the point that it is negatively affecting the availability of nutrients to native plants. Grass and forb cover may be very sparse or clumped. Mat-forming forbs, shortgrasses, and shrubs dominate the plant community. Mid-stature perennial bunchgrass species (e.g., needle and thread) may exist, but only in small patches or under shrub canopy. This could occur due to overgrazing (failure to adjust stocking rate to declining forage production due to increased invasive dominance), a long-term lack of fire, or the introduction of invasive species. In the most severe stages of degradation, there is a significant amount of bare ground, and large gaps occur between plants. Large patches of prickly pear cactus are common. Potential exists for soils to erode to the point that irreversible damage may occur. This is a critical shift in the ecology of the site. Soil erosion combined with a lack of organic matter deposition due to sparse vegetation creates changes to the hydrology, soil chemistry, soil microorganisms, and soil structure to the point where intensive restoration is required to restore the site to another state or community. Changing management (i.e., improving grazing management) cannot create sufficient change to restore the site within a reasonable time frame. This state is characterized by soil surface degradation and little plant soil surface cover. In this plant community, browsing on shrubs is common, and shrubs will take on a hedged look. This community has lost soil or vegetation attributes to the point that recovery to the Reference State will require major reclamation efforts, e.g., soil rebuilding, intensive mechanical treatments, and reseeding, that will require large amounts of capital and time that will be economically unfeasible. Acknowledging this, the Shortgrass-Shrub Community will be considered a terminal community that will not return to the reference state because of degraded soil conditions and the loss of higher successional native plant species. Key factors in the approach to transition include: a decrease in grass canopy cover and production; an increase in shrub canopy cover; increases in mean bare patch size; increases in soil crusting; decreases in the cover of cryptobiotic crusts; decreases in soil aggregate stability; or evidence of erosion, including water flow patterns and litter movement.

State 4
Invaded State

The Invaded State is identified as being in the exponential growth phase of invader abundance, where control is a priority. Dominance (or relative dominance) of noxious or invasive species reduces species diversity, forage production, wildlife habitat, and site protection. A level of 20 percent invasive species composition by dry weight indicates that a substantial energy input will be required to create a shift to the grassland state (herbicide, mechanical treatment), even with a return to proper grazing management or favorable growing conditions. Prescriptive grazing can be used to manage invasive species. In some instances, carefully targeted grazing (sometimes in combination with other treatments) can reduce or maintain the species composition of invasive species. The community within this state will follow a pathway beyond restoration if the invasive or noxious species continue to thrive without mechanical, biological, or chemical control methods and are allowed to exceed 25 percent of species composition by dry weight. The invasive nature of the weed outcompetes the present plant community. Once the weed reaches its maximum population level for this site, effective control is unlikely without massive resource inputs. Ecological processes at a site may change after an invading species has established and spread (Walker and Smith 1997). These changes include reduced site stability, reduced infiltration rates, and reduced production of desirable species.

Community 4.1
Invaded Community

Community in this state may be structurally indistinguishable from the bunchgrass state except that invasive/noxious species exceed 20 percent of species composition by dry weight. This community may also be similar to the Degraded Shortgrass State (3) except that invasive/noxious species exceed 20 percent of species composition by dry weight. Although there is no research to document the level of 20 percent, this is estimated to be the point in the invasion process following the lag phase based on interpretation of Masters and Sheley 2001. For aggressive invasive species (i.e., spotted knapweed) a 20 percent threshold could be less than 10 percent. Early in the invasion process there is a lag phase where the invasive plant populations remain small and localized for long periods before expanding exponentially (Hobbs and Humphries 1995). Production in the invaded community may vary greatly. A site dominated by spotted knapweed, where soil fertility and chemistry remain near reference, may have production near that of the reference community. A site with degraded soils and an infestation of cheatgrass may produce only 10 to 20 percent of the reference community. Once invasive species dominate the site, either in species composition by weight or in their impact on the community the threshold has been crossed to the Invaded State (4). As invasive species such as spotted knapweed, cheatgrass, and leafy spurge become established, they become very difficult to eradicate. Therefore considerable effort should be placed in preventing plant communities from crossing a threshold to the Invaded State (4) through early detection and proper management. Preventing new invasions is by far the most cost-effective control strategy, and typically places an emphasis on education. Control measures used on the noxious plant species impacting this ecological site include chemical, biological, and cultural control methods. The best success has been found with an integrated pest management (IPM) strategy that incorporates one or several of these options along with education and prevention efforts (DiTomaso 2000).

State 5
Conifer Encroached State

The Conifer Encroached State may contain as many as four different phases. The Early Phase, Mid Phase, Late Phase, and Closed Phase are defined by the amount of encroachment and age class of the stand. This state typically occurs in response to a combination of long-term fire suppression, grazing history, and increase atmospheric carbon dioxide. The trigger for transition is a coniferous expansion of greater than two stems per acre.

Community 5.1
Conifer Encroach Community

Rocky Mountain juniper (Juniperus scopulorum), limber pine (Pinus flexilis), ponderosa pine (Pinus ponderosa), and Douglas fir (Pseudotsuga menziesii) encroachment is common on this ecological site and is generally focused in areas where the mountains of MLRA 44B transition quickly to MLRA 43B. Under the Reference State, no conifers should exist on this site. It is also noted that all states may transition to the Conifer Encroached State; however, encroachment is most likely to occur in the Altered State, where there is an increase in bare ground due to a combination of factors that allows seed-to-soil contact with reduced competition. Fire suppression and improper grazing management are the two most common triggers. The exact mode in which conifers begin to encroach varies; however, the trend points to a combination of 1 or more of the following: repeated moderately heavy to heavy grazing; reduced (non-existent) fire frequency; increased atmospheric carbon; and a generally warmer climate compared to that of pre-settlement. When heavy grazing occurs, areas in the plant canopy open, allowing for seed dispersal by bird or overland flow via rills on neighboring sites. The effects of conifer encroachment are not immediately noticeable, but over time, as the conifer canopy increases, light and water interception increase, which reduces opportunities for herbaceous plants. One paper (Barrett, 2007) suggests that for precipitation to penetrate the juniper canopy, events must be greater than 0.30 inches. Increased tree canopy creates perching sites for predators, which reduces site suitability for greater sage grouse. More information is needed on the full extent and impact of juniper encroachment on these plant communities for an approved ecological site description. Studies (Miller et al., 2000) based in an area similar to the Rocky Mountain juniper community of Montana suggest following a phased approach to characterizing the juniper stand. Not unlike the western juniper community discussed in Miller et al., the Conifer Encroached Communities of Montana exhibit three or four different phases based, at this time, on qualitative experience. Phase I (Early) is defined by actively expanding conifer cover with generally less than 10 percent canopy cover and the trees’ limbs generally touching the ground. This early stage generally has not completely lost its hydrologic functions, but herbaceous plant communities may show signs of reduced production and species richness. Control methods include mechanical removal and prescribed fire. Prescribed fire is still effective in this phase as it still contains the necessary native plants for recovery. The tree canopy is also low enough that the risk of a dangerously hot fire is reduced. Phase II (Midphase) is still actively expanding, but canopy cover may reach 15 to 25 percent, and due to the more mature trees, seed production is very high. This Midphase begins to highly restrict herbaceous and shrubby plants, and junipers tend to be codominant. Hydrology is departing from reference, with rills becoming longer and, in isolated areas, erosional gullies possible. Control methods for the Midphase should focus on mechanical treatment, as there is a high risk of catastrophic and potentially sterilizing fire. Phase III (Late Phase) is where conifer cover exceeds 25 percent and has slowed as a forest condition. Lower tree limbs begin to die, and the shrub cover is nearly gone. Traveling through this community is increasingly difficult. Conifers become the dominant plant, with herbaceous plant production greatly decreasing. Bare ground increases, and hydrologic function is nearly lost compared to a grass or shrub community. The late phase should focus more on restoration than control, as the necessary plants will likely not be present to cross the threshold back to a rangeland situation. Because soil stability and hydrologic function are lacking in this phase, mechanical juniper removal will be required. Phase IV (Closed Phase) is the steady state forest, where the system is nearly devoid of rangeland plants. The trees stop producing seed and begin to close in on each other. This phase is impassable, and nearly all light and precipitation are intercepted. Bare ground may be reduced due to excessive forest duff layer. As a result, soil chemistry slowly changes due to acidification from conifer needles. The closed phase is extremely rare in this LRU for two reasons. 1) This phase takes upwards of 100 years to occur and even under suppression, fire will control these sites 2) Management often occurs before trees are allowed to reach this phase. The presence of sagebrush stumps indicates that the historical plant community was rangeland, preventing the misclassification of historic coniferous forests (often more than 100 years old).

Transition T1A
State 1 to 2

The Reference State (1) transitions to the Altered State (2) if bluebunch wheatgrass, by dry weight, decreases to below 25 percent or if bare ground cover is increased beyond 20 percent. The driver for this transition is loss of taller bunchgrasses, which creates open areas in the plant canopy with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Altered State. There are several other key factors signaling the approach of transition T1A: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability and/or evidence of erosion including water flow patterns, development of plant pedestals, and litter movement. The trigger for this transition is improper grazing management and/or long-term drought leading to a decrease in bluebunch wheatgrass composition to less than 25 percent and reduction in total plant canopy cover.

Transition T1B
State 1 to 3

The Reference State (1) transitions to the Degraded State (3) when bluebunch wheatgrass is removed from the plant community and needle and thread is codominant with short-statured bunchgrasses such as Sandberg bluegrass. This transition differs from T1A in that it is usually quick and associated with disturbances like repeated overgrazing or heavy human traffic. This rapid transition is generally realized where livestock are confined to small pastures for long periods of time, such as horse pastures and calving lots. The driver for this transition is the loss of taller bunchgrasses, which creates openings in the canopy and exposes bare soil. Soil erosion reduces soil health, causing transitions to a Degraded State. There are several other key factors signaling the approach of transition T1B: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability, and/or evidence of erosion including water flow patterns, development of plant pedestals, and litter movement. The trigger for this transition is improper grazing management, long term drought, and/or heavy human disturbance.

Transition T1C
State 1 to 4

Healthy plant communities are most resistant to invasion. However, regardless of grazing management, without some form of active weed management (chemical, mechanical, or biological control) and prevention, the Reference State (1) can transition to the Invaded State (4) in the presence of aggressive invasive species such as spotted knapweed, leafy spurge, and cheatgrass. This will occur even if the reference community is thriving. The Central Rocky Mountain Valleys tend to resist invasion of cheatgrass; however, repeated heavy grazing or intense human activities can open the interspaces of the bunchgrass community and allow for encroachment. Long-term stress conditions for native species (e.g., overgrazing, drought, and fire) accelerate this transition. If populations of invasive species reach critical levels, the site transitions to the Invaded State. The trigger for this transition is the presence of aggressive invasive species. The species composition by dry weight of invasive species approaches 10 percent.

Transition T1D
State 1 to 5

The transition from the Reference State (1) to the Conifer Encroached State (5) is driven primarily by long-term fire suppression but heavy grazing may contribute to increased bare ground for seeding sites. Encroachment often occurs fastest within 200 feet of the seed source. The trigger for transition is a conifer stem count higher than 2 per acre.

Restoration pathway R2A
State 2 to 1

The Altered State (2) has lost soil or vegetation attributes to the point that recovery to the Reference State (1) will require reclamation efforts such as soil rebuilding, intensive mechanical and cultural treatments, and/or revegetation. Grazing management is necessary for an effective restoration process. Such management can include rest rotation or seasonal deferment to allow deep-rooted grasses to grow and establish either via seed or reproductive tillers. Grazing sessions should be light and brief in order to avoid grazing regrowth. Low-intensity prescribed fires are used to reduce competitive increaser plants like needle and thread and Sandberg bluegrass. A low intensity fire will also reduce Wyoming big sagebrush densities. Fire should be carefully planned or avoided in areas prone to annual grass infestation.

Transition T2A
State 2 to 3

As improper grazing management continues, the vigor of bunch grasses will decrease and the shorter grasses and shrubs will increase, contributing to the Degraded State (3). Prolonged drought will provide a competitive advantage to shrubs, allowing them to become co-dominant with grasses. The canopy cover of shrubs will increase above 15 percent. Key transition factors include: an increase in native shrub canopy cover; a reduction in bunchgrass production; a decrease in total plant canopy cover and production; increases in mean bare patch size; increases in soil crusting; decreases in the cover of cryptobiotic crusts; decreases in soil aggregate stability; and/or evidence of erosion, including water flow patterns and litter movement.

Transition T2B
State 2 to 4

Invasive species can occupy the Altered State (2) and drive it to the Invaded State (4). The Altered State is at risk if invasive seeds and/or other viable material are present. The driver for this transition is more than 10 percent of the dry weight of aggressive weeds and 20 percent for other weedy species.

Transition T2C
State 2 to 5

The transition from the Altered State (2) to the Conifer Encroached State (5) is driven primarily by long-term fire suppression but long-term heavy grazing may contribute to increased bare ground for seeding sites. Encroachment often occurs fastest within 200 feet of the seed source. The trigger for transition is a conifer stem count higher than 2 stems per acre.

Transition T3A
State 3 to 4

Invasive species can occupy the Degraded State (3) and drive it to the Invaded State (4). The Degraded State is at risk of this transition occurring if invasive seeds or viable material are present. The driver for this transition is the presence of critical population levels (more than 10 percent of the dry weight of aggressive invasive species and 20 percent for other weedy species). The trigger is the presence of seeds or viable material from invasive species. This state has sufficient bare ground that the transition could occur simply due to the presence or introduction of invasive seeds or viable material. This is particularly true of aggressive invasive species such as spotted knapweed. This transition could be assisted by overgrazing (failure to adjust stocking rate to declining forage production), a long-term lack of fire, or an extensive drought.

Transition T3B
State 3 to 5

The transition from the Degraded State (3) to the Conifer Encroached State (5) is driven primarily by long-term heavy grazing and increased bare ground for seeding sites. Encroachment often occurs fastest within 200 feet of the seed source. The trigger for transition is a conifer stem count higher than 2 per acre.

Restoration pathway R4A
State 4 to 1

Extensive invasive weed control paired with grazing management is particularly effective when invasive species are limited and the existing plant community resembles that of the Reference State. To return an invaded community to the Reference State, significant time and capital investments may be required.

Restoration pathway R4B
State 4 to 2

If invasive species are removed before remnant populations of bunchgrass are drastically reduced, the Invaded State (4) can revert to its Altered State. The driver for the reclamation pathway is weed management with reseeding. Continued Integrated Pest Management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life.

Restoration pathway R4C
State 4 to 3

If invasive species are removed before native species' remnant populations are drastically reduced, the Invaded State can revert to the Degraded State. The driver for the reclamation pathway is weed management with reseeding. Continued Integrated Pest Management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life.

Transition T4A
State 4 to 5

The transition from the Invaded State (4) to the Conifer Encroached State (5) is driven primarily by long-term fire suppression but long-term heavy grazing may contribute to increased bare ground for seeding sites. Encroachment often occurs fastest within 200 feet of the seed source. The trigger for transition is a conifer stem count higher than 2 per acre.

Restoration pathway R5A
State 5 to 1

Restoration efforts may simply focus on the removal of coniferous trees and shrubs to restore the Conifer Encroached State (5) to the Reference State (1), depending on the level of conifer canopy cover and its impact on rangeland health. If following and utilizing the phases established by Miller et al., management and restoration methods will vary. A majority of the conifer encroachment in MLRA 44B will fall into the early two phases of Miller's phases. When conifers are removed through brush management and/or prescribed fire, Phase I may reveal none-to-slight to moderate deviations from rangeland health. If mechanical removal of conifers is utilized, no grazing management is needed, assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short-term grazing deferment and/or rest are suggested. In a short period of time, removing a Phase I encroachment will return the site to its original state. Proactive pest management is encouraged. Phase II encroachment may require a more intensive mechanical removal of trees and shrubs, with prescribed fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a moderate departure from Reference, suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g., reduced mid-statured bunchgrasses), increased rill frequency and length, and possibly more bare ground. Increased post-treatment grazing management may be necessary. Grazing management may be as simple as short-term growing season deferment; however, long-term rest may be necessary in the latter stages of Phase II encroachment. The latter stages of Phase II encroachment will likely require some short-term erosion mitigation, such as straw waddles, as well as range planting and/or critical area planting to re-establish any loss of native herbaceous plants, particularly mid-statured cool-season bunchgrasses. Phase III encroachment canopy cover resembles forested sites with larger trees and shrubs. Prior to any prescribed burning, forest management-style tree removal (removal of woody debris and logs from the site) will be required to prevent the fire from burning too hot. The result of a prescribed fire on this site is typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since the Shallow Droughty ecological site for 44B LRU 01 Subset A is a dry site, herbaceous plants will likely have been depleted under a Phase III encroachment. This means there is an opportunity for large areas of bare ground, increased rilling, and, in some cases, gully erosion. Post-treatment will require range planting and/or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be required to ensure the establishment of any new seedlings.

Restoration pathway R5B
State 5 to 2

The Conifer Encroached State (5) Phases I and II will generally resemble the Altered State (2) on this site. If following and utilizing the phases established by Miller et al., management and restoration methods will vary. A majority of the conifer encroachment in MLRA 44B will fall into the early two phases of Miller's phases. When conifers are removed through brush management and/or prescribed fire, Phase I may show none-to-slight to moderate deviations from rangeland health. If mechanical removal of conifers is utilized, no grazing management is needed, assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short-term grazing deferment and/or rest are suggested. In a short period of time, removing a Phase I encroachment will return the site to its original state. Proactive pest management is encouraged. Phase II encroachment may require a more intensive mechanical removal of trees and shrubs, with prescribed fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a moderate departure from Reference, suggesting an overall instability of the site such as reduced herbaceous production, reduced functional and structural groups (e.g., reduced mid-statured bunchgrasses), increased rill frequency and length, and possibly more bare ground. Increased post-treatment grazing management may be necessary. Grazing management may be as simple as short-term growing season deferment; however, long-term rest may be necessary in the latter stages of Phase II encroachment. The latter stages of Phase II encroachment will likely require some short-term erosion mitigation such as straw waddles as well as range planting and/or critical area planting to re-establish any loss of native herbaceous plants, particularly mid-statured cool-season bunchgrasses. Phase III encroachment canopy cover resembles forested sites with larger trees and shrubs. Prior to any prescribed burning, forest management-style tree removal (removal of woody debris and logs from the site) will be required to prevent the fire from burning too hot. The result of a prescribed fire on this site is typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since the Shallow Droughty ecological site for 44B LRU 01 Subset A is a dry site, herbaceous plants will likely have been depleted under a Phase III encroachment. This means there is an opportunity for large areas of bare ground, increased rilling, and, in some cases, gully erosion. Post-treatment will require range planting and/or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be required to ensure the establishment of any new seedlings.

Restoration pathway R5C
State 5 to 3

The Conifer Encroached State (5) Phases II and III may resemble the Degraded State (3) on this site. If following and utilizing the phases established by Miller et al., management and restoration methods will vary. An overwhelming majority of the conifer encroachment in MLRA 44B will fall into the early two phases of Miller's phases. This restoration pathway is extremely rare because managing a degraded state is typically not cost-effective for land managers. When conifers are removed through brush management and/or prescribed fire, Phase I may show none-to-slight to moderate deviations from rangeland health. If mechanical removal of conifers is utilized, no grazing management is needed, assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short-term grazing deferment and/or rest are suggested. Given a short time removal of a Phase I encroachment will recover to Reference. Proactive pest management is encouraged. Phase II Encroachment may require a more intensive mechanical removal of trees and shrubs, with prescribed fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a moderate departure from Reference, suggesting an overall instability of the site such as reduced herbaceous production, reduced functional and structural groups (e.g., reduced mid-statured bunchgrasses), increased rill frequency and length, and possibly more bare ground. Increased post-treatment grazing management may be necessary. Grazing management may be as simple as short-term growing season deferment; however, long-term rest may be necessary in the latter stages of Phase II encroachment. The latter stages of Phase II encroachment will likely require some short-term erosion mitigation, such as straw waddles, as well as range planting and/or critical area planting to re-establish any loss of native herbaceous plants, particularly mid-statured cool-season bunchgrasses. Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The results of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since the Shallow Droughty ecological site for 44B LRU 01 Subset A is a dry site, herbaceous plants will likely have been depleted under a Phase III encroachment. This means there is an opportunity for large areas of bare ground, increased rilling, and, in some cases, gully erosion. Post-treatment will require range planting and/or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be required to ensure the establishment of any new seedlings.

Additional community tables

Table 9. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production (kg/hectare)	Foliar cover (%)
Grass/Grasslike
1	Deep Rooted Bunchgrasses			314–650
	bluebunch wheatgrass	PSSP6	Pseudoroegneria spicata	336–616	35–50
	green needlegrass	NAVI4	Nassella viridula	67–112	5–10
	Indian ricegrass	ACHY	Achnatherum hymenoides	22–45	1–5
	rough fescue	FECA4	Festuca campestris	0–11	0–1
2	Shortgrasses			67–112
	Sandberg bluegrass	POSE	Poa secunda	22–45	5–10
	prairie Junegrass	KOMA	Koeleria macrantha	22–45	5–10
	blue grama	BOGR2	Bouteloua gracilis	0–22	0–5
	needleleaf sedge	CADU6	Carex duriuscula	6–22	1–3
	threadleaf sedge	CAFI	Carex filifolia	6–22	1–3
4	Rhizomatous Grasses			22–90
	thickspike wheatgrass	ELLA3	Elymus lanceolatus	22–67	0–5
	western wheatgrass	PASM	Pascopyrum smithii	22–67	0–5
	plains reedgrass	CAMO	Calamagrostis montanensis	11–22	0–2
Shrub/Vine
3	Shrubs			34–101
	Wyoming big sagebrush	ARTRW8	Artemisia tridentata ssp. wyomingensis	67–90	5–15
	little sagebrush	ARAR8	Artemisia arbuscula	0–45	0–5
	yellow rabbitbrush	CHVI8	Chrysothamnus viscidiflorus	22–45	1–4
	spineless horsebrush	TECA2	Tetradymia canescens	22–45	1–3
	Woods' rose	ROWO	Rosa woodsii	11–34	0–3
	broom snakeweed	GUSA2	Gutierrezia sarothrae	0–22	0–2
	chokecherry	PRVI	Prunus virginiana	0–17	0–5
	black sagebrush	ARNO4	Artemisia nova	0–11	0–3
	currant	RIBES	Ribes	0–11	0–3
	plains pricklypear	OPPO	Opuntia polyacantha	0–1	0–1
Forb
5	Forbs			11–45
	arrowleaf balsamroot	BASA3	Balsamorhiza sagittata	6–22	0–5
	American vetch	VIAM	Vicia americana	6–17	0–3
	dotted blazing star	LIPU	Liatris punctata	6–17	0–3
	stemless mock goldenweed	STAC	Stenotus acaulis	0–11	0–3
	spiny phlox	PHHO	Phlox hoodii	0–6	0–3
	Bonneville shootingstar	DOCO	Dodecatheon conjugens	0–6	0–3
	common yarrow	ACMI2	Achillea millefolium	0–6	0–3
	desertparsley	LOMAT	Lomatium	0–6	0–3
	bastard toadflax	COUM	Comandra umbellata	0–6	0–3
	milkvetch	ASTRA	Astragalus	0–6	0–2
	Lava aster	IOAL	Ionactis alpina	0–6	0–1
Tree
6	Coniferous Trees/Tall Shrubs			0–11
	ponderosa pine	PIPO	Pinus ponderosa	0–11	0–1
	Douglas-fir	PSME	Pseudotsuga menziesii	0–11	0–1
	Rocky Mountain juniper	JUSC2	Juniperus scopulorum	0–11	0–1
	limber pine	PIFL2	Pinus flexilis	0–11	0–1

Interpretations

Animal community

This site provides a variety of wildlife habitats for an array of species. Prior to the settlement of this area, large herds of antelope, elk, and bison roamed. Though the bison have been replaced, mostly with domesticated livestock, elk and antelope still frequently utilize this largely intact landscape for winter habitat in areas adjacent to forests. Sites with large quantities of curl-leaf mountain mahogany are considered important winter range for mule deer, elk, and moose. In some areas, it may even be considered critical habitat for dwindling wild ungulate populations.

Managed livestock grazing is suitable on this site due to the potential to produce an abundance of high quality forage. This is often a preferred site for grazing by livestock, and animals tend to congregate in these areas. In order to maintain the productivity of the site, grazing on adjoining sites with less production must be managed carefully to make sure utilization on this site is not excessive. Management objectives should include maintenance or improvement of the native plant community. Careful management of the timing and duration of grazing is important. Shorter grazing periods and adequate deferment during the growing season are recommended for plant maintenance, health, and recovery. According to McLean et al., early-season defoliation of bluebunch wheatgrass can result in high mortality and reduced vigor in plants. They also suggest, based on prior studies, that the opportunity for regrowth is necessary before dormancy to reduce injury bluebunch.

Since needle and thread normally matures earlier than bluebunch wheatgrass and produces a sharp awn, this species is usually avoided after seed set. Changing the grazing season will allow needle and thread to be used more efficiently.

Continual non-prescribed grazing of this site will be injurious, will alter the plant composition and production over time, and will result in the transition to the Altered State. The transition to other states will depend on the duration of poorly managed grazing as well as other circumstances such as weather conditions and fire frequency.

The Altered State can degrade further to the Degraded State or the Invaded State. Management should focus on grazing management strategies that will prevent further degradation, such as seasonal grazing deferment or winter grazing where feasible. Communities within this state are still stable and healthy under proper management. Forage quantity and/or quality may be substantially decreased from the Reference State.

Grazing is possible in the Invaded State. Invasive species are generally less palatable than native grasses. Forage production is typically greatly reduced in this state. Due to the aggressive nature of invasive species, sites in the Invaded State face an increased risk of further degradation. Grazing has to be carefully managed to avoid further soil loss and degradation and possible livestock health issues.

Prescribed grazing can be used to manage invasive species. In some instances, carefully targeted grazing (sometimes in combination with other treatments) can reduce or maintain the species composition of invasive species. In the Degraded State, grazing may be possible but is generally not economically or environmentally sustainable.

Hydrological functions

The hydrologic cycle functions best in the Reference State (1) with good infiltration and deep percolation of rainfall; however, the cycle degrades as the vegetation community declines. Rapid rainfall infiltration, high soil organic matter, good soil structure, and good porosity accompany high bunchgrass canopy cover. High ground cover reduces raindrop impact on the soil surface, which keeps erosion and sedimentation transport low. Water leaving the site will have a minimal sediment load, which allows for high water quality in associated streams. High rates of infiltration will allow water to move below the rooting zone during periods of heavy rainfall. The Bluebunch Wheatgrass Community (1.1) should have no rills or gullies present, and drainage ways should be vegetated and stable. Water flow patterns, if present, will be barely observable. Plant pedestals are essentially nonexistent. Plant litter remains in place and is not moved by wind or water.

Improper grazing management results in a community shift to the Mixed Bunchgrass Community (1.2). This plant community has a similar canopy cover, but bare ground may increase to more than 15 percent. Therefore, the hydrologic cycle is functioning at a level similar to the water cycle in the Bluebunch Wheatgrass Community (1.1). Compared to the Community (1.1), the infiltration rates are slightly reduced, and surface runoff is slightly higher.

In the Degraded State (3) and the Invaded State (4), canopy and ground cover are greatly reduced compared to the Reference State (1), which impedes the hydrologic cycle. Infiltration will decrease and runoff will increase due to reduced ground cover, the presence of shallow-rooted species, rainfall splash, soil capping, reduced organic matter, and poor structure. Sparse ground cover and decreased infiltration can combine to increase the frequency and severity of flooding within a watershed. Soil erosion is accelerated, the quality of surface runoff is poor, and sedimentation increases.

The hydrology of the Conifer Encroached State (5) is highly variable, but studies suggest that an increased tree canopy affects the interception of rainfall as well as the amount of available soil moisture for herbaceous vegetation. This can negatively affect infiltration and increase runoff.

Recreational uses

This site is often utilized for photography, hiking, hunting, bird watching, and flower collecting.

Supporting information

Inventory data references

Information presented was derived from a similar site's Range Site Description (Shallow 9 –14” P.Z., Northern Rocky Mountain Valleys, South, East of Continental Divide), NRCS clipping data, literature, field observations, and personal contacts with range-trained personnel (i.e., used professional opinion of agency specialists, observations of land managers, and outside scientists).

References

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Barrett, H. 2007. Western Juniper Management: A Field Guide.
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Bestelmeyer, B. and J. Brown. 2005. State-and-Transition Models 101: A Fresh look at vegetation change.
Blaisdell, J.P. 1958. Seasonal development and yield of native plants on the Upper Snake River Plains and their relation to certain climate factors.
Blaisdell, J.P. and R.C. Holmgren. 1984. Managing Intermountain Rangelands--Salt-Desert Shrub Ranges. General Tech Report INT-163. USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, UT. 52.
Bunting, S.C., B.M. Kilgore, and C.L. Bushey. 1987. Guidelines for Prescribe burning sagebrush-grass rangelands in the Northern Great Basin. General Technical Report INT-231. USDA Forest Service Intermountain Research Station, Ogden, UT. 33.
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Contributors

Kirt Walstad
Benjamin Moore
Braden Pitcher
Ken Scalzone
Eve Wills

Approval

Kirt Walstad, 9/08/2023

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)	Grant Petersen
Contact for lead author	grant.petersen@usda.gov
Date	11/23/2024
Approved by	Kirt Walstad
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
Rills will primarily be absent on gentle slopes however on the steepest of slopes of this site (greater than 30 percent) small, short rills (less than 2-3 feet) may be evident after high precipitation events.
Presence of water flow patterns:
Water flow patterns are rare in the reference condition. If present, they are most likely to occur on steeper slopes (greater than 20 percent) and are inconspicuous, disconnected, and very short in length.
Number and height of erosional pedestals or terracettes:
Pedestals are not evident in the reference condition.
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Number of gullies and erosion associated with gullies:
Bare ground is between 20-30 percent.
Extent of wind scoured, blowouts and/or depositional areas:
Amount of litter movement (describe size and distance expected to travel):
Wind scoured, or depositional areas are not evident in the reference condition.
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil Surface Stable with Stability Ratings of 4-6 (both under canopy and bare). Biotic crusts and or root mats may be present.
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Structure trends to weak, fine granular. The A horizon is approximately 3 inches thick with wet Munsell colors Value 5 or less, Chroma 3 or less. Dry colors tend to be quite light prior to wetting. Official Series Description (OSD) for characteristic range.
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Evenly distributed across the site, bunchgrasses improve infiltration while rhizomatous grass protects the surface from runoff forces. The Shallow droughty ecological site is well drained and has a moderately rapid infiltration rate. An even distribution of mid stature grasses, ~60-70% of site production, cool season rhizomatous grasses 10% of site production along with a mix of shortgrass (5-15%), forbs and shrubs (5-10%).
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
Not Present
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:
Mid-statured, cool season, perennial bunchgrasses

Sub-dominant:
rhizomatous grass = perennial shortgrasses/grasslikes > shrubs = forbs >> trees

Other:

Additional:
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Mortality in herbaceous species is not evident. Species with bunch growth forms may have some natural mortality in centers.
Average percent litter cover (%) and depth ( in):
Total litter cover ranges from 30-35 percent. Most litter is irregularly distributed on the soil surface and is not at a measurable depth.
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Average annual production is 800. Low: 550 High 1050 pounds per acre. Production varies based on effective precipitation and natural variability of soil properties for this ecological site.
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:
Potential invasive (including noxious) species (native and non-native). Invasive species on this ecological site include (but not limited to) annual brome spp., spotted knapweed, yellow toadflax, leafy spurge, ventenata, crested wheatgrass, etc.

Native species such as Rocky Mountain juniper, Ponderosa pine, broom snakeweed, rabbitbrush spp., blue grama, Sandberg’s bluegrass, etc. when their populations are significant enough to affect ecological function, indicate site condition departure.
Perennial plant reproductive capability:
In the reference condition, all plants are vigorous enough for reproduction either by seed or rhizomes in order to balance natural mortality with species recruitment. Density of plants indicates that plants reproduce at level sufficient to fill available resource.

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Natural ResourcesConservation Service

Ecological site EX044B01A138

Shallow Droughty (SwDr) LRU 01 Subset A

Last updated: 9/08/2023 Accessed: 11/23/2024

General information

MLRA notes

LRU notes

Classification relationships

Ecological site concept

Associated sites

Similar sites

Table 1. Dominant plant species

Legacy ID

Ecosystem states

States 1, 5 and 2 (additional transitions)

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

Natural Resources
Conservation Service

Last updated: 9/08/2023
Accessed: 11/23/2024