Mountain Very Steep Shallow Loam (mountain big sagebrush)
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1a
introduction of exotic species,
More details -
Transition T2a
Lack of fire and continued heavy livestock grazing during the growing season
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Transition T3a
Wildfire or prescribed fire
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The Reference State is a description of this ecological site just prior to Euro-American settlement but long after the arrival of Native Americans. The description of the Reference State was determined by NRCS Soil Survey Type Site Location information and familiarity with rangeland relict areas where they exist. The dominant plant communities found on these sites would have depended on the time since last wildfire. The fire return interval on these sites averaged between 30 and 40 years. Immediately following wildfire (1.2a) herbaceous species would have been dominant with a mixture of native perennial forbs and grasses. Forbs would have included tapertip hawksbeard (Crepis acuminata), arrowleaf balsamroot (Balsamorhiza sagittata), sticky purple geranium (Geranium viscosissimum), and shortstem buckwheat (Eriogonum brevicaule), and grasses would have included bluebunch wheatgrass (Pseudoroegneria spicata), muttongrass (Poa fendleriana), and slender wheatgrass (Elymus trachycaulus) (1.1). With increased time since the last wildfire (1.1a), mountain big sagebrush (Artemisia tridentata ssp. vaseyana) would have ultimately regained its dominance on the site (1.2). Several mountain shrub species would have also been present including antelope bitterbrush (Purshia tridentata) and mountain snowberry (Symphoricarpos oreophilus). The native perennial herbaceous understory of these sites would have had increased productivity and richness at higher elevations, resembling more of a sagebrush-steppe environment. A more complete list of species by lifeform for the Reference State is available in the accompanying tables in the “Plant Community Composition by Weight and Percentage” section of this document.
Submodel
Description
State 2 is identical to State 1 in form and function, with the exception of the presence of non-native plants and animals, possible extinctions of native species, and a different climate. State 2 is a description of the ecological site shortly following Euro-American settlement. This state can be regarded as the current potential. The balance between shrubs and herbs would be dependent upon the length of time elapsed since the last wildfire. Immediately following fire (2.2a), the site will be in an herb-dominated phase (2.1). Following a period without fire (2.1a) mountain big sagebrush will become dominant, with a mixture of native perennial forbs and grasses in the understory (2.2). The shrub-steppe variety tends to occur at higher elevations. Dominant grasses are bluebunch wheatgrass, muttongrass, and slender wheatgrass. Forbs include tapertip hawksbeard, arrowleaf balsamroot, and sticky purple geranium, among others. Some non-native species may be present. This State is maintained by periodic wildfire and by a healthy, productive, and diverse plant community that can provide native seed sources and promotes soil stability, water infiltration, and soil moisture retention. The resiliency of this State will be maintained by a reduction in livestock grazing pressure. Conversely, continued heavy season-long livestock grazing will negatively impact the resiliency of this State.
Submodel
Description
In the absence of fire, and with continued heavy impacts from livestock grazing, the native herbaceous understory will markedly decrease, allowing the shrubs, mainly mountain big sagebrush, to become super-dominant and take over the site (3.1). This State is maintained by the abundance of seed source for mountain big sagebrush and a corresponding lack of native perennial seed source for herbaceous species. The resiliency of this State can be maintained by deferring livestock grazing pressure during the growing season. Conversely, the resiliency of this State will be negatively impacted by continued season-long heavy livestock grazing. This State may also experience accelerated soil erosion, which will negatively impact the resiliency of this State.
Submodel
Description
Yellow rabbitbrush and some common disturbance-following herbaceous species such as houndstongue (Cynoglossum spp.), tarweed (Madia spp.), and cheatgrass (Bromus tectorum) will increase following fire (4.1), whether prescribed or wild, while the mountain big sagebrush will be lost. This State could be maintained by periodic fire.
Submodel
Mechanism
The simultaneous introduction of exotic species, both plants and animals, possible extinctions of native flora and fauna, and climate change has caused State 1 to transition to State 2. Reversal of such historic changes (i.e. a return pathway) back to State 1 is not practical.
Mechanism
Lack of fire and continued heavy livestock grazing during the growing season of grasses will cause a transition into the Mountain Big Sagebrush Super-dominance State. During the time period between 1860 and 1950, most of these sites experienced heavy grazing pressure and have therefore transitioned to the Mountain Big Sagebrush Super-dominance State. The approach to this transition is indicated by a loss of perennial grasses and forbs in the understory and an increase in the shrub component relative to the grasses and forbs. This transition is triggered by sustained heavy grazing, which has often occurred since Euro-American settlement.
Mechanism
Wildfire or prescribed fire will temporarily remove the mountain big sagebrush. However, an increase in yellow rabbitbrush (Chrysothamnus viscidiflorus) will follow the removal of sagebrush in most circumstances. The herbaceous component may also increase after fire. The approach to this transition is indicated by a drastic decrease in forage species and increased fuel loads. The trigger causing this transition is fire.
Model keys
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The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.