State 1
Perennial Grasses/Shrubs

The Perennial Grasses/Shrubs State (State 1) is the reference state for the Igneous ecological site. The prominent cover of bluebunch wheatgrass, king-spike fescue and other mid-stature cool-season bunchgrasses with perennial forbs and a mix of black sagebrush, Wyoming big sagebrush, and fringed sagewort make for a productive and stable site.

Characteristics and indicators. Bluebunch wheatgrass is the dominant herbaceous species on this site, shrubs are less prominent on this landscape, but are found scattered within the community. Sagebrush cover will vary across this site in response to underlying geology. In limestone interbeds black sagebrush is the dominant woody cover, and in sedimentary interbeds Wyoming big sagebrush prevails.

Resilience management. The hardiness of the vegetation that thrive within the harsh conditions of the soil characteristics of the Igneous ecological site create a plant community resistant to change. But once disturbed, the herbaceous component of this site is difficult to restore, reducing the resiliency of the community.

Community 1.1
Bluebunch Wheatgrass/Mixed Shrub

Figure 8. Bluebunch wheatgrass is dominant in the Reference Community.

The reference plant community for the Igneous ecological site is the Bluebunch Wheatgrass/Mixed Shrub plant community. This community evolved with grazing by large herbivores, and an occasional wildfire. The shallow depth to bedrock, generally steeper slopes, and droughty nature of the soils for this community prevents sagebrush from being the dominant landscape. Potential vegetation is about 75% grasses or grass-like plants, 15% forbs, and 10% woody plants. The major grasses include bluebunch wheatgrass, spike fescue, prairie junegrass, and rhizomatous wheatgrass. Woody plants are black and Wyoming big sagebrush and fringed sagewort. A variety of forbs also occurs in this plant community and plant diversity is high (see Plant Composition Table). The total annual production (air-dry weight) of this state is about 350 pounds per acre, but it can range from about 250 lbs./acre in unfavorable years to about 500 lbs./acre in above average years.

Resilience management. This plant community is extremely stable and well adapted to the Central Rocky Mountains climatic conditions. The diversity in plant species allows for high drought tolerance. This is a sustainable plant community (site/soil stability, watershed function, and biologic integrity).

Community 1.2
Perennial Bunchgrasses/Mixed Shrub

Figure 11. As the Reference State degrades, the at-risk community increases in short-stature bluegrasses and prairie Junegrass as bluebunch wheatgrass decreases.

Historically, this plant community evolved under grazing by large ungulates and a low fire frequency. Currently, it occurs under moderate, season-long grazing by livestock and is exacerbated by prolonged drought conditions. Shrubs are significant components of this plant community. Cool-season grasses make up the majority of the understory with the balance made up of miscellaneous forbs. Dominant grasses include prairie junegrass, western wheatgrass and of less frequency bluebunch wheatgrass. Grasses of secondary importance include bluegrasses, and needleandthread. Forbs commonly found in this plant community include hawksbeard, fleabane, buckwheat, phlox, and sandwort. Shrubs such as black sagebrush, fringed sagewort, Wyoming big sagebrush, and rubber rabbitbrush can make up to 20% of the total annual production. When compared to the Reference plant community, fringed sagewort and rubber rabbitbrush, bluegrasses, and prairie junegrass have increased. Production of specific species such as bluebunch wheatgrass and spike fescue, has been reduced. The total annual production (air-dry weight) of this state is about 300 pounds per acre, but it can range from about 200 lbs./acre in unfavorable years to about 450 lbs./acre in above average years.

Resilience management. Rangeland Health Implications/Indicators: This plant community is resistant to change. The herbaceous species present are well adapted to grazing; however, species composition can be altered through long-term overgrazing. The herbaceous component is mostly intact and plant vigor and replacement capabilities are sufficient. Water flow patterns and litter movement is not uncommon especially on steeper slopes. Incidence of pedestalling is minimal but normal. Soils are mostly stable and the surface shows minimum soil loss. The watershed is functioning and the biotic community is intact.

Pathway CP 1.1-1.2
Community 1.1 to 1.2

Bluebunch Wheatgrass/Mixed Shrub

Perennial Bunchgrasses/Mixed Shrub

Moderate, continuous season-long grazing will convert the Reference plant community to the Perennial Grasses/Mixed Shrubs plant community. Prolonged drought will exacerbate this transition. Repetitive increased utilization of the grasses in this community and lack of moisture impacts the taller structure of this community, and encourages the shorter statured plants.

Pathway CP 1.2-1.1
Community 1.2 to 1.1

Perennial Bunchgrasses/Mixed Shrub

Bluebunch Wheatgrass/Mixed Shrub

Prescribed grazing with drought management will convert this plant community to the Reference Community. The probability of this occurring is high especially if varied season of use and periods of rest are allowed as part of the prescribed method of use. Stabilization practices following fire or disturbance will aid the recovery of this community as well.

State 2
Short Grass

The Sod-former/Sagebrush ecological site is a low-stature community that has shifted from the cool-season bunchgrasses to tillering grass-likes (threadleaf sedge). Fringed sagewort and pricklypear cactus are common.

Characteristics and indicators. The prominent cover is threadleaf sedge. Scattered sagebrush may persist with rubber rabbitbrush and skunkbush sumac. Season of use and species of grazing ungulate will be a factor affecting this cover. The sagebrush cover is dwarfed or droughty in appearance and is reduced in vigor by the shift in hydrology of this community. Most other mid-stature cool-season bunchgrasses are limited to within the canopy of the sagebrush or within the protective cactus clumps.

Resilience management. The dense root map of threadleaf sedge makes this community extremely resistant to change, and resilient to disturbance. Although the establishment of threadleaf sedge is a slow process, it will recover with time. Removal of grazing or disturbance does not provide a shift in the herbaceous cover within this community. The overall health and vigor of both the herbaceous as well as woody cover will improve with the removal of the grazing pressure or disturbance from the community.

Community 2.1
Threadleaf Sedge/Bluegrass

Figure 14. Threadleaf sedge will become dominant in a dispersed patchwork pattern in degraded communities.

The Threadleaf Sedge/Bluegrass plant community is created when the Reference State plant communities (1.1 and 1.2) are subjected to extended drought or intense storms, especially when under high intesntity yearlong grazing. Threadleaf sedge and weedy annuals are the most dominant plants. Threadleaf sedge will be more scattered (less dense in growth) than other similar communities. Compared to the Reference State, cactus and fringed sagewort have invaded significantly. Cool-season mid-stature grasses are absent or severely decreased. Threadleaf sedge is the dominant cover. Shrubs are limited on the Igneous ecological site, and plant diversity is low. Rubber rabbitbrush is advantageous in the open canopy of the Igneous ecological site with black sagebrush and Wyoming big sagebrush. However, heavy browsing by large ungulates will significantly reduce or remove the limited shrub cover. Shadscale saltbush can also be found on this site. The total annual production (air-dry weight) of this state is about 250 pounds per acre, but it can range from about 100 lbs./acre in unfavorable years to about 400 lbs./acre in above average years.

Resilience management. This plant community is relatively stable and resistant to overgrazing. Sod forming grasses are effectively competing against the establishment of perennial mid-stature cool-season grasses. Plant diversity is altered and the herbaceous component is not intact. Recruitment of perennial grasses is limited. The biotic integrity is missing. On areas with a well established sod plant community, water infiltration is affected, but not to the extent as deeper soils. While this sod protects the area itself, adjacent on-site and off-site areas are impacted by runoff that can cause rill channels and gully erosion. Water flow patterns and pedestalling are obvious. The watershed may or may not be functional.

State 3
Invaded

Cheatgrass or downy brome (Bromus tectorum) is an aggressive annual invader that threatens rangelands across the west, including Wyoming. The ability of cheatgrass to persist through the winter under a blanket of snow and grow early allow it to take advantage of early spring precipitation and snowmelt (winter annual). Multiple growth cycles throughout a year leaves a thick litter (duff) layer and builds a significant seedbank. This annual invader has an aggressive growth habit that creates a hostile environment for most native species, including sagebrush. Climatic shifts, changes in management, and exposure to human activity are a few of the explanations for the current flush and rapid expanse across the western United States. Although cheatgrass is the most prevalent large-scale threat for rangeland managers, a variety of thistles, in combination with other aggressive invaders such as toadflax are increasing in density and frequency. Each species produces their own set of challenging management issues. As new species are identified, or as other species become more prevalent on a large-scale, the community dynamics in this State will shift in response to the concerns of the identified species.

Characteristics and indicators. This State is characterized by the presence and then dominance of invasive/non-native species. The competitive nature of annuals and other invasive species, creates a complex environment that inhibits control, and makes it implausible to attain complete eradication once an invasive species has established on the landscape. Increased access, increased travels of individuals, and other natural and man-made disturbances has opened the door for invasion in most native communities.

Resilience management. The lack of tools to achieve complete eradication, and variable success on long-term reduction of most invasive species has led to this State being resilient and resistant to change. The shallow depth, slope, and access to these areas limit the ability and cost effectiveness to treat. Mechanical means to treat invasions are generally not recommend, and so not transition to a disturbed condition is modeled. However, under select circumstances, mining and other human activities including wildfire may create such a transition.

Community 3.1
Native Grasses/Invasive Species/Sagebrush

The Perennial Grasses/Invasive Species/Sagebrush community phase has maintained a representative composition of native perennial grasses and forbs that are key to this ecological site with the accompanying Black or Wyoming big sagebrush component. This community phase (4.1) is characterized by a significant composition of invasive species (5 percent or greater) on the landscape. These invasive species have a wider scale of distribution; rather than one isolated patch in an isolated portion of the landscape. Extent of improvement is limited, and the cost and labor required determines the economic feasibility. Access and slope of the specific location increases the cost and decreases the feasibility of restoring a desired community. The depth to bedrock in combination with access and slope makes this community phase, the “At-Risk” community. Litter cover within this phase is increasing with the duff layer specifically associated with cheatgrass. This duff layer creates a barrier that can impede water infiltration and increase runoff, accelerating erosion. This is aggravated with increased slope. The age and extent of the cheatgrass stand will determine the extent of duff in the system. Production yields of the perennial grasses and forbs are reduced but the total production will maintain or may be slightly elevated due to the overall biomass and expanded growth potential of many of the annual or invasive species. A specific production range is not provided due to the variability of composition that will affect overall production.

Resilience management. Rangeland Health Implications/Indicators: Plant diversity is moderate for this phase, with perennial grasses, forbs, and shrub components still present, sustaining the diversity of the community. The plant vigor is reduced, and replacement capabilities are limited due to the limited moisture and nutrients available after cheatgrass has sprouted. Plant litter is noticeably more when compared to reference communities due to the potential biomass produced by the invasive species (species dependent). Soil erosion is minimal but will vary with species; as is the water flow patterns and pedestalling. Infiltration is unaltered or slightly reduced; however, as the duff layer or litter builds, infiltration will decrease, and runoff will increase.

State 4
Disturbed

Disturbance to these highly erodible soils (whether it was mechanical, cultural, or natural) reduced the resilience or resistance to support native vegetation or the ability to respond to management in the same manner as an undisturbed site. Changes to soil structure and hydrologic processes reduce the stability and ability to recover. Reclamation or restoration of an area is limited or restrictive due to slope, access, and lack of depth to bedrock. These "altered" lands may, after significant inputs and time, resemble the Reference Communities (1.1 or 1.2), but they will not respond or function the same as the Reference State. One catastrophic event or several smaller disturbances can lead to the transition to the Altered State from any identified state within the State-and-Transition Model. The soils have not been altered to the extent that they are outside the site characteristics, but the potential has shifted enough that it will not respond like the Reference State. The time required to allow the redevelopment of structure and the cryptogrammic crust is beyond the natural function of management. The initial flush of vegetation is annual forbs, including mustards, a successional plant community. The site begins its own recovery, but the time required to return to the original conditions (pre-disturbance) can be extensive. The site, however, may become similar in composition to the Reference State.

Characteristics and indicators. The Disturbed State is characterized by a landscape that has had significant soil disturbance. Early successional plant communities, evidence of mining, or the presence of introduced species (crested wheatgrasses, russian wildrye, etc.) are indicators of this State.

Resilience management. Stabalization and preservation of as much soil as possible is the mechanism to provide resiliency to this State. The use of mulch or other slope stabilization materials will help in reducing erosional impact and allowing vegetation to establish.

Community 4.1

Disturbed or degraded lands are characterized by alteration of the soils to a degree that the functionality (erosional, depositional, hydrological, or chemical) and potential of the soils has been impacted. Site-specific evaluations need to be completed to determine the level of effect. The method and severity of alternation, as well as the spatial extent of the disturbance will determine vegetation response and management needs. Linear disturbances, such as trails and roads, will hold a different risk than patchwork or polygonal disturbances, such as well-pads or parking areas. Small-scale or isolated disturbances (spot fires, prairie dog town) can be just as significant of a risk as a large-scale disturbance (mine lands). The growth curve of this plant community will vary depending upon the successional or seeded species that are able to establish in an area. For an accurate growth curve, a site-specific species inventory and documentation of the climatic tendencies should be collected.

Resilience management. Rangeland Health Implications/Indicators: This plant community is variable and, depending upon the age of the stand and the stage of successional tendencies, determines how stable (resilient/resistant) the community is. Plant diversity is low for successional communities. This flexibility within the community creates a variable level of biotic integrity. In areas of new or frequent disturbance, annual weedy species or early successional plants will be the dominant cover, providing some diversity, but gives minimal structural cover for wildlife. As the site matures or as the period between disturbances is lengthened, perennial or taller-statured, stronger-rooted species will increase providing protection and help to improve hydrologic processes and stability to allow grasses and shrubs to begin to establish. Soil erosion is dependent on the disturbance regime and the biotic integrity of the community which determines water flow, infiltration, and runoff. Other factors that are influential are surface roughness and brokenness (tire tracks, hoof action, smoothed, denuded surfaces, trails that may concentrate water flow).

Transition T 1-2
State 1 to 2

Frequent and severe (year-long or continuous season-long ) grazing or compaction from surface traffic, will convert the plant community to a Threadleaf Sedge Sod Plant Community. The impact to of frequent or repeated hits during grazing, hoof impact, and lack of rest for recovery weakens and removes the key grass species in the community. As the mid-stature grasses decline, threadleaf sedge is able to increase and alter the hydrology of the site.

Constraints to recovery. The dense root mat formed by threadleaf sedge alters the hydrology, effectively removing moisture from the site, limiting the available resources for other native species. The dense sod also limits the available soil space for seedling establishment. Interpspaces between sod patches are prone to erosion and runoff (limited infiltration of moisture).

Transition T 1-3
State 1 to 3

Drought, soil disturbances, or high-intensity grazing with a seed source present can open the soil surface and weaken the community allowing invasive species to establish. Although not common, fire can provide the niche for cheatgrass to establish on this site.

Constraints to recovery. Once invasive species, especially cheatgrass, establish, it is costly and difficult (if even possible) to remove. The lack of the key grass species also limits recover of this site.

Transition T 2-3
State 2 to 3

Drought, or drought with grazing intensity together, weakens a water limited system allowing invasive species the opportunity to take advantage of the limited moisture. Threadleaf sedge has been seen to die back or die out with prolonged drought opening the canopy and the community’s vulnerability to invasive species. Disturbance by mechanical means or human activities that break the root masses or disturb the soil surface open this closed community to potential invasive species, especially when there is a readily available seed source for those invasive species.

Constraints to recovery. The sod of threadleaf sedge will continue to impact the hydrology and competition for limited resources in this community limiting the potential for recovery. The lack of other key herbaceous species also is a constraint on this site. The inability, at this time, to eradicate cheatgrass does not allow for a complete recovery of an invaded community.

Transition T 4-3
State 4 to 3

Any disturbance that occurs or stress that is placed on the herbaceous cover, weakens the canopy and allows for invasive species to establish if a seed source is present. This State is at high risk of transitioning to an Invaded State. The challenge of successful seedings on a very shallow soils and steep slopes leaves the community vulnerable to invasion.

Constraints to recovery. The challenge of eradicating or reducing invasive species such as cheatgrass prevents recovery of most invaded communities without significant inputs for weed control, seeding with long-term grazing management.