Natural Resources
Conservation Service
Mountain Stony Loam (antelope bitterbrush)
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
More details -
Transition T3A
Excessive big game use
More details -
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 least modified plant community would have been dominated by antelope bitterbrush (Purshia tridentata), primarily occurring on south-facing slopes, with a rich and productive native perennial herbaceous understory. Mountain big sagebrush (Artemisia tridentata ssp. vaseyana) and birch-leaf mountain mahogany (Cercocarpus montanus) would have been common shrub associates. The majority of the grass component would have been bluebunch wheatgrass (Pseudoroegneria spicata), and forbs would have included a mixture of common yarrow (Achillea millefolium), Wyoming Indian paintbrush (Castilleja linariifolia), western stoneseed (Lithospermum ruderale), and buckwheats (Eriogonum spp.), among others (1.1). A more complete list of species by lifeform for the Reference State is available in 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. Antelope bitterbrush is the dominant shrub with a mixture of predominately native perennial herbaceous species. Grasses include a slightly diminished bluebunch wheatgrass, slender wheatgrass (Elymus trachycaulus), and Letterman’s needlegrass (Achnatherum lettermanii). Forbs include common yarrow, Wyoming Indian paintbrush, western stoneseed, and buckwheats, among others (2.1). Key indicators of the approach to this transition are the loss of perennial grass understory and an increase in the shrub component relative to grasses. Sustained heavy grazing and fire exclusion over time (decades) will trigger this transition.
Submodel
Description
In the absence of fire, but with continued heavy impacts from livestock grazing, the native herbaceous understory will markedly decrease, allowing the certain shrubs, mainly mountain big sagebrush, to gain in dominance (3.1). Antelope bitterbrush will also decline because of heavy use by sheep as well as big game. The root-sprouting ability of bitterbrush is a key factor affecting the resiliency of this state. Stability of this state will be maintained by reducing livestock and wildlife ungulate use, while continued heavy use by livestock and wildlife will reduce state stability.
Submodel
Description
Due to heavy browsing impacts from local mule deer populations, antelope bitterbrush suffers immensely, and Utah juniper will invade. The herbaceous understory will also be depleted due to continued heavy livestock grazing.
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.
Transition T2A
Lack of fire and continued heavy livestock grazing during the growing season
Mechanism
Lack of fire and continued heavy livestock grazing during the growing season of grasses, throughout the 1860s to the 1950s, caused a transition into a Mountain Big Sagebrush/ Reduced Antelope Bitterbrush State.
Mechanism
During the period between the 1940s and the 1950s a dramatic increase was seen in local mule deer populations. The impacts from their heavy browsing particularly on the antelope bitterbrush, combined with continued fire suppression, further reduced the bitterbrush to its near removal on some sites, allowing both mountain big sagebrush and Utah juniper to take over the site. Key indicators of the approach to this transition are the loss of vigor in bitterbrush and an increase in sagebrush and juniper reproduction and establishment. Excessive big game use triggers this transition.
Model keys
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Ecological sites
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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.
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